Solvent: PDX; T= 60–70 °C; Thermogelling material. [140,143]

from

lecular hydrogels, self-healing materials.

and insects [169].

Polysaccharides are abundant in nature, no matter whether in plants or animals, and are important for in vivo functions. As observed in Figure 6, there is a wide variety of polysaccharides, but the most abundant ones are cellulose and chitin. Cellulose provides structure to the cell walls of plants. Chitin, on the other side, is part of the exoskeletons of crustaceans, shellfish, and insects [169]. Polysaccharides are abundant in nature, no matter whether in plants or animals, and are important for in vivo functions. As observed in Figure 6, there is a wide variety of polysaccharides, but the most abundant ones are cellulose and chitin. Cellulose provides structure to the cell walls of plants. Chitin, on the other side, is part of the exoskeletons of crustaceans, shellfish,

**Figure 6.** Cellulose and chitin structures (top). II: schematic diagram of crystalline structures for different forms of chitin. Source: Adapted with permission from Jun-ichi Kadokawa (2015). Fabrication of nanostructured and microstructured chitin materials through gelation with suitable dispersion media: RSC Adv. 5 12736 [169]. Copyright © 2021 The Royal Society of Chemistry. **Figure 6.** Cellulose and chitin structures (top). II: schematic diagram of crystalline structures for different forms of chitin. Source: Adapted with permission from Jun-ichi Kadokawa (2015). Fabrication of nanostructured and microstructured chitin materials through gelation with suitable dispersion media: RSC Adv. 5 12736 [169]. Copyright © 2021 The Royal Society of Chemistry.

for chitin have been developed [169]: (a) bulky structure; (b) insolubility in water and typical organic solvents; (c) it is harmful Chitin is an abundant but only marginally used biomass. There are several reasons why not many practical applications for chitin have been developed [169]: (a) bulky structure; (b) insolubility in water and typical organic solvents; (c) it is harmful to recover chitin, since the available procedures require the use of strong acids and bases; (d) native chitin from crustaceans, which have exoskeletons that protect animals from their predators, has fibrous structures rich in proteins and minerals; and (e) there is a need to remove mineral and protein constituents in order to isolate chitin.

Chitin is an abundant but only marginally used biomass. There are several reasons why not many practical applications

Chitosan was developed to overcome the drawbacks of chitin. Chitosan is commercially attractive for production of biocompatible polymers for environmental and biomedical applications [30]. It is basically a copolymer of N-acetyl-D-glucosamine and D-glucosamine. It is obtained from the hydration of chitin. This hydration takes place in alkaline solutions in a temperature range of 80–140 ◦C during 10 h [170,171].

Chitosan is a cationic polysaccharide, produced by deacetylation of chitin. Deacetylation proceeds to different levels depending on the intended uses. The physical properties of chitosan, particularly solubility, depend on molecular weight and degree of deacetylation of the material [172–174].

Modification of chitosan leads to a diversity of derivates, with differentiated properties. As shown in Figure 1 of Deng et al. [174], different chitosan moieties are possible. Each one of them is produced from grafting or other chemical or enzymatic modification forms. They differ in antimicrobial activity. Further studies on chitin-chitosan modification are available in the literature [58,175–178].

#### *3.2. Polymer Backbones*

Polymer backbones are the most common substrates for grafting modification. Several techniques can be used to create many possible combinations. Most of these developments are focused on property improvement for industrial applications. They include synthesis of adhesives; reinforcement of mechanical properties; improvement of chemical resistance; synthesis of electro, optical, thermo responsive polymers; health care applications; and self-healing polymers, among others [179].

Polymer grafting techniques have been reported since the late 1950s [8,9,11]. Polymers based on acrylamide and acrylonitrile using polymer grafting techniques are included in the early reports. However, the huge increase in research related to synthesis of materials with controlled microstructures using polymer grafting techniques has been possible due to the advances in reversible deactivation radical polymerization (RDRP) techniques over the last three decades [180–184]. The main RDRP routes are nitroxide mediated polymerization (NMP) [185], reversible addition fragmentation transfer polymerization (RAFT) [180,186,187], and atom transfer radical polymerization (ATRP) [71,188], although there are other polymer synthesis techniques, such as ring-opening polymerization (ROP) [181] and click chemistry, among others, that can be used. Another important aspect in polymer grafting is the solvent used for the reaction, particularly when grafting proceeds as a heterogenous process. As observed in Table 19, solvents such as supercritical fluids, mainly supercritical carbon dioxide, water, DMF, or combinations of solvents are typically used for polymer grafting. These techniques have improved our skills to produce molecularly well-defined, chain-end tethered polymer brush films. The assets of RDRP have substantially impacted the synthesis and properties of surface-grafted polymers. Although vinyl monomers are widely use in graft polymerization for backbones or side-arms, other monomers coming from natural sources are increasingly being used. That is the case, for instance, of ε-caprolactone, lactic acid [189], L-lactide, and butyrolactone. It is also observed in Table 19 that other nontraditional monomers such as acrylamide (AM), N-isopropylacrylamide (NIPAAM), and acrylates and methyl acrylates, such as methyl methacrylate (MMA) and acrylic acid (AA), are being increasingly used in polymer grafting applications. To get a glimpse of the focus of research papers that involve polymer grafting as the chemical route for polymer modification, Table 5 summarizes journal reports on polymer grafting from the current period (2020–2021). As expected, an increasing trend toward the improvement of natural biopolymers using synthetic polymer arms is observable.

**Table 5.** Recent reports on the production of materials using polymer grafting (2020–2021).


**Table 5.** *Cont.*


#### **Table 5.** *Cont.*


<sup>a</sup> Searching criteria used in Scopus: (TITLE ("-g-") AND TITLE-ABS-KEY ("poly") AND TITLE-ABS-KEY ("graft")).



**Thermogravimetric analysis** 

**Differential scan-**

bones and grafted materials.

**(DSC)** 

bones and grafted materials.

analyses to focus on the grafts only.

**Size exclusion chromatography** 

**(SEC)** 

**Size exclusion chromatography** 

**Differential scanning calorimetry** 

**(SEC)** 

**Size exclusion** 

analyses to focus on the grafts only.

This is utilized to evaluate changes in crystallinity through the thermal behavior between back-

It allows determination of molecular weight averages (MW) and molecular weight distributions

It allows determination of molecular weight averages (MW) and molecular weight distributions (MWD) of grafted chains [230], which must be separated from the backbone before carrying out the

This is used to study changes in thermal decomposition profiles between backbones and grafted

This is utilized to evaluate changes in crystallinity through the thermal behavior between back-

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It allows determination of molecular weight averages (MW) and molecular weight distributions (MWD) of grafted chains [230], which must be separated from the backbone before carrying out the

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It allows determination of molecular weight averages (MW) and molecular weight distributions (MWD) of grafted chains [230], which must be separated from the backbone before carrying out the

**Size exclusion chromatography** 

**(SEC)** 

**Differential scanning calorimetry** 

analyses to focus on the grafts only.

This is utilized to evaluate changes in crystallinity through the thermal behavior between back-


**ler** 

**Lignin** 

**Lignin** 

Imidazole and POCl3 react in to (1H-imidazol-1-yl)phosphonic group which reacts with lignin

TGA

Imidazole and POCl3 react in to (1H-imidazol-1-yl)phosphonic group which reacts with lignin

TGA

TGA

Lignin-g-IPG = 483 °C.

nitrogen flow.

°C.

PHRR (kW/m2)//THR (MJ/m2) PP =1350 kW/m2//87.3 MJ/m2,

MDT values for lignin derivatives and PP blends. Lignin MDT = 398 °C. Lignin-g-IPG MDT > 600 °C.

PP/Lignin = 382/333 kW/m2//76 MJ/m2,

Lignin-g-IPG = 483 °C.

°C.

PHRR (kW/m2)//THR (MJ/m2) PP =1350 kW/m2//87.3 MJ/m2, PP/Lignin = 382/333 kW/m2//76 MJ/m2,

FR

PP =418°C, PP/Lignin = 472 °C, PP/20 °% Lignin-g-IPG = 479 °C, PP/30 °%

SDTQ600 thermal analyzer; 20 °C/min under nitrogen, from ambient to 600

[125,135]

FR

FR

PSBMA, PSBMAH, PSBMAEO

PP =1350 kW/m2//87.3 MJ/m2,

MDT values for lignin derivatives and PP blends. Lignin MDT = 398 °C. Lignin-g-IPG MDT > 600 °C.

PP/Lignin = 382/333 kW/m2//76 MJ/m2,

Thermal stability of biocomposites.

PP =418°C, PP/Lignin = 472 °C, PP/20 °% Lignin-g-IPG = 479 °C, PP/30 °%

Q5000 TGA system (TA Instruments); 25 to 600 °C, at 10 °C/min, 25 mL/min

Two MDT values were found for all samples 380 °C and 430 °C.

SDTQ600 thermal analyzer; 20 °C/min under nitrogen, from ambient to 600

[125,135]


**Cellulosic filter papers** 

trile.

Radiation-induced graft (RIGCP) copolymerization of acryloni-

TGA Analyses obtained in TGA-50 (Shimadzu).

Heating rate: 10 °C/min. N2 environment. [121]

*Processes* **2021**, *9*, 375 **Thermogravimetric analysis** 

**(TGA)** 

materials.

**(DSC)** 

bones and grafted materials.

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It allows determination of molecular weight averages (MW) and molecular weight distributions (MWD) of grafted chains [230], which must be separated from the backbone before carrying out the

**Size exclusion chromatography** 

**(SEC)** 

**Differential scanning calorimetry** 

analyses to focus on the grafts only.

This is utilized to evaluate changes in crystallinity through the thermal behavior between back-

This is used to study changes in thermal decomposition profiles between backbones and grafted


**CellClAc** 

**CellClAc** 

**Chitosan** 

N'N'-MBA

N'N'-MBA

Embedded polymerization N-VP, 4VP. Crosslinking agent:

**Chitosan** 

Embedded polymerization N-VP, 4VP. Crosslinking agent:

TGA

TGA

mL/min nitrogen environment.

Heating from 20 °C to 400 °C at 10 °C/min.

mL/min nitrogen environment.

Heating from 20 °C to 400 °C at 10 °C/min.

TGA analyses carried out using a NETZSCH, STA 409 PG.4.G Luxx. 50

**Table 8.** Summary of spectroscopic characterization techniques employed in grafted materials.

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 

**Table 8.** Summary of spectroscopic characterization techniques employed in grafted materials.

TGA analyses carried out using a NETZSCH, STA 409 PG.4.G Luxx. 50

[164]

[164]

NCHA, 4VP, DA and DAAM grafted by atom transfer radical polymerization (ATRP) using CuCl, 2′2′BIPI as catalyst.

TGA

TGA

NCHA, 4VP, DA and DAAM grafted by atom transfer radical polymerization (ATRP) using CuCl, 2′2′BIPI as catalyst.

gen environment (10 mL/min).

gen environment (10 mL/min).

Thermal analyses carried out in a Shimadzu TGA-50 at 10 °C/min in nitro-

ramp.

[122]

[122]

Cell-g-DA and Cell-g-4VP exhibited higher decomposition temperatures.

Cell-g-DA and Cell-g-4VP exhibited higher decomposition temperatures.

Thermal analyses carried out in a Shimadzu TGA-50 at 10 °C/min in nitro-


dride grafted over PHA (by dou-

**Cellulose nanocrystal (CNC)** 

Macromolecular initiator obtained from the reaction between Br-iBuBr and CNC with TEA as catalyst via SI-ATRP with sTY. Material was casted in PMMA.

TGA

DSC

enthalpy of fully crystalline PLLA.

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Samples analyzed in a Pyris Diamond TG/DTA equipment (STA449C/3/F,

German).

Sample weight: 14.2 mg.

Heating/Cooling rate: 10 °C/min. Flow of nitrogen: 20 mL/min. TGA Thermal degradation of studied materials analyzed in a TGA/SDTA 851e in nitrogen atmosphere. Heating from 30 to 550 °C, at 10 °C/min. DSC Tg determined in a Pyris 1 DSC equipment. Heating from 30 to 200 °C at 10

Analyses carried out in a TGA Q50 (TA Instruments), under nitrogen atmosphere (20 mL/min). Heating from 30 to 500 °C at 5, 10, 15, 20, 25 and 30

°C/min for determination of degradation activation energy.

Analyses performed in a Star 1 (Mettler- Toledo). Heating from 25 °C to 200 °C at 5 °C/min, remaining at 200 °C for 5 min. Cooling to −50 °C at 20 °C/min, remaining there for 5 min, followed by heating to 200 °C at 5 °C/min. Tg, Tm, Tc were measured. Crystallinity (v) calculated from melting

[119]

°C/min.

[118]

**Cellulose** 

**Cellulose nanocrystal (CNC)** 

Macromolecular initiator obtained from the reaction between Br-iBuBr and CNC with TEA as catalyst via SI-ATRP with sTY. Material was casted in PMMA.

**(DP=1130)** APS and MMA embedded. TGA-DTA


DSC

DSC

DSC

DSCQ10 (TA Instruments). Hermetic pan (T 090127).

DSCQ10 (TA Instruments). Hermetic pan (T 090127).

DSCQ10 (TA Instruments). Hermetic pan (T 090127).

Heating from 25 to 165 °C at 10 °C/min. Cooling to 15 °C followed by heat-

Heating from 25 to 165 °C at 10 °C/min. Cooling to 15 °C followed by heat-

Heating from 25 to 165 °C at 10 °C/min. Cooling to 15 °C followed by heat-

resolution.

resolution.

**Hemicellulose** 

**Hemicellu-**

**Hemicellulose** 

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TGA/DSC 1 STARe System (Mettler Toledo). 5–15 mg of a sample. Nitrogen

TGA/DSC 1 STARe System (Mettler Toledo). 5–15 mg of a sample. Nitrogen

TGA/DSC 1 STARe System (Mettler Toledo). 5–15 mg of a sample. Nitrogen

environment (85 mL/min).

environment (85 mL/min).

environment (85 mL/min).

Heating from 30–500 °C at 10 °C/min.

Heating from 30–500 °C at 10 °C/min.

Heating from 30–500 °C at 10 °C/min.

Compositions of produced gases measured in an FTIR (TA, Nicolet, iS); detector coupled to TGA. FTIR analyses from 4000 to 650 cm−1 with a 4 cm−1 resolution. [37]

Compositions of measured in an FTIR (TA, iS); decoupled TGA. FTIR analyses from 4000 650 cm−1 with a 4 cm−1

Compositions of produced gases measured in an FTIR (TA, Nicolet, iS); detector coupled to TGA. FTIR analyses from 4000 to 650 cm−1 with a 4 cm−1 [37]

[37]


**Chitosan** 

**Chitosan** 

**Chitosan** 

**Table 8.** Summary of spectroscopic characterization techniques employed in grafted materials.

**Table 8.** Summary of spectroscopic characterization techniques employed in grafted materials.

**Table 8.** Summary of spectroscopic characterization techniques employed in grafted materials.

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 

**CellClAc** 

**CellClAc** 


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**CellClAc** 

**CellClAc** 

**CellClAc** 

Macro initiator, Cu(I)Cl/2′2′ BIPI catalytic system via ATRP

Macro initiator, Cu(I)Cl/2′2′ BIPI catalytic system via ATRP

Macro initiator, Cu(I)Cl/2′2′ BIPI catalytic system via ATRP

spectrometer at room temperature in DMSO-d6.

spectrometer at room temperature in DMSO-d6.

spectrometer at room temperature in DMSO-d6.

1H-NMR NMR spectra obtained using a Bruker 400 MHz

FTIR FTIR data using solid samples as KBr pellets, from 4000 cm−1 to 450 cm−1.

FTIR FTIR data using solid samples as KBr pellets, from 4000 cm−1 to 450 cm−1.

FTIR FTIR data using solid samples as KBr pellets, from 4000 cm−1 to 450 cm−1.

[109]

[109]

[109]

of 4NPA and MMA

of 4NPA and MMA

of 4NPA and MMA


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materials.

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It allows determination of molecular weight averages (MW) and molecular weight distributions (MWD) of grafted chains [230], which must be separated from the backbone before carrying out the

**Size exclusion chromatography** 

**(SEC)** 

**Differential scanning calorimetry** 

analyses to focus on the grafts only.

This is utilized to evaluate changes in crystallinity through the thermal behavior between back-

This is used to study changes in thermal decomposition profiles between backbones and grafted

**(TGA)** 

**Thermogravimet-**

**(DSC)** 

bones and grafted materials.

**Lignin** 

**Lignin** 

Imidazole and POCl3 react in to (1H-imidazol-1-yl)phosphonic group which reacts with lignin

TGA

Lignin-g-IPG = 483 °C.

°C.

PHRR (kW/m2)//THR (MJ/m2) PP =1350 kW/m2//87.3 MJ/m2, PP/Lignin = 382/333 kW/m2//76 MJ/m2,

FR

Imidazole and POCl3 react in to (1H-imidazol-1-yl)phosphonic group which reacts with lignin

Lignin-g-IPG = 483 °C.

Thermal stability of biocomposites.

°C.

TGA

PHRR (kW/m2)//THR (MJ/m2) PP =1350 kW/m2//87.3 MJ/m2,

nitrogen flow.

PP/Lignin = 382/333 kW/m2//76 MJ/m2,

MDT values for lignin derivatives and PP blends. Lignin MDT = 398 °C. Lignin-g-IPG MDT > 600 °C. PP =418°C, PP/Lignin = 472 °C, PP/20 °% Lignin-g-IPG = 479 °C, PP/30 °%

SDTQ600 thermal analyzer; 20 °C/min under nitrogen, from ambient to 600

[125,135]

FR

SDTQ600 thermal analyzer; 20 °C/min under nitrogen, from ambient to 600

Q5000 TGA system (TA Instruments); 25 to 600 °C, at 10 °C/min, 25 mL/min

Two MDT values were found for all samples 380 °C and 430 °C.

[125,135]


C3H6O.

Solvents: DMSO, PDX, DMAc,

materials.

vent.

1H-NMR

**Thermogravimetric analysis (TGA)** 

**(DSC)** 

bones and grafted materials.

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It allows determination of molecular weight averages (MW) and molecular weight distributions (MWD) of grafted chains [230], which must be separated from the backbone before carrying out the

**Size exclusion chromatography** 

**(SEC)** 

Redox initiator FAS-H2O2 for grafting of MA, and KPS for polymerization of MA.

**Cellulosic**  *Grewia optiva* **fi-**

**bers** 

**Differential scanning calorimetry** 

analyses to focus on the grafts only.

This is utilized to evaluate changes in crystallinity through the thermal behavior between back-

FTIR Chemical structures of fibers before and after grafting were studied using FTIR

(PERKIN ELMER RXI). Spectrum recorded from 4000 to 400 cm−1. [110]

This is used to study changes in thermal decomposition profiles between backbones and grafted

Spectra of studied materials obtained using a Bruker WM-400 apparatus, at 300 MHz. Tetramethyl silane (TMS) used as internal standard and DMSO-d6 as sol-

FR

**Microcrystalline cellulose** 

**ler** 

**Lignin** 

Imidazole and POCl3 react in to (1H-imidazol-1-yl)phosphonic group which reacts with lignin

TGA

Lignin-g-IPG = 483 °C.

°C.

PHRR (kW/m2)//THR (MJ/m2) PP =1350 kW/m2//87.3 MJ/m2, PP/Lignin = 382/333 kW/m2//76 MJ/m2,

FR

Ring-opening polymerization

PSBMA, PSBMAH, PSBMAEO

**macrocontrol-**

derivatives.

PP =1350 kW/m2//87.3 MJ/m2,

PP/Lignin = 382/333 kW/m2//76 MJ/m2,

Thermal stability of biocomposites.

with a drop of trifluoroacetic acid-d; internal standard: tetramethyl silane (TMS). [116]

60◦ . Two MDT values were found for all samples 380 °C and 430 °C.

Q5000 TGA system (TA Instruments); 25 to 600 °C, at 10 °C/min, 25 mL/min

[134]

(ROP) of L-LA with DMAP in 1H-NMR Materials analyzed using 1H-NMR (Bruker AV400-MHz). Solvent: DMSO-d6

TGA

nitrogen flow.

MDT values for lignin derivatives and PP blends. Lignin MDT = 398 °C. Lignin-g-IPG MDT > 600 °C. PP =418°C, PP/Lignin = 472 °C, PP/20 °% Lignin-g-IPG = 479 °C, PP/30 °%

SDTQ600 thermal analyzer; 20 °C/min under nitrogen, from ambient to 600

[125,135]


**crystal (CNC)** 

charge-corrected to 284.8 eV.

1.541 Å); incidence angle: 10 to 40°, 0.07° steps.

charge-corrected to 284.8 eV.

charge-corrected to 284.8 eV.

alyzed surface: 400 mm2. Atomic concentrations estimated from areas of photoelectron peaks considering atomic sensitivity factors. All binding energies were

XPS analyses performed in an ESCALAB 250 equipment (Thermo Scientific). Analyzed surface: 400 mm2. Atomic concentrations estimated from areas of photoelectron peaks considering atomic sensitivity factors. All binding energies were

XPS

XPS

casted in PLLA.


**Cellulose** 

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an ionic liquid AmimCl to form

XRD WAXD UV spectroscopy

UV analyses performed in a UV2000 equipment (UNICO, China), to follow the

load and controlled release of vitamin C.

FTIR A TENSOR27 FTIR apparatus (4500–400 cm−1) was used to analyze materials.

WAXD carried out using an XRD-6000 X-ray diffractometer (Shimadzu, Japan); Ni-filtered Cu Ka radiation (40 kV, 30 mA); 4°/min at ambient temperature.

Cellulose-*g*-PLLA

**Cellulosic filter** 

Radiation-induced graft (RIGCP) copolymerization of

XRD

XRF

to estimate crystallinity index (CI).

XRF analyses performed using a Philips wavelength dispersive equipment X' Unique II, including flow and scintillation (fs) detectors. Qualitative analyses of chelating filter paper-metal complexes were obtained by X-ray fluorescence. FTIR A Nicolet Nexus spectrophotometer with single reflection ATR was used. Range:

4000 to 700 cm−1. Resolution: 4 cm−1; 60 scans.

kin Elmer-1650 FTIR apparatus.

XRD analyses of studied materials in an angle range 2θ = 5–50° were obtained in a Shimadzu XRD-610 equipment, with Cu Kα radiation (1.5418°A). Operating conditions: 8 °/min and 1.0 s; 30 kV and 20 mA. Peak height methods were used

[121]

**papers** 

**Hemicellulose** 

mers

**CellClAc** 

NCHA, 4VP, DA and DAAM grafted by ATRP using CuCl, 2′2′BIPI as catalyst.

13C-NMR HSQC

Hemicellulose grafting using TBD and ε-caprolactone mono-

[37] 1H-NMR

1H COSY. 16 scans and 256 increments for 2D 1H–13C HSQC.

FTIR Apparatus: Perkin Elmer Spectrum One. Solid samples as KBr pellets.

[122] UV-Visible Apparatus: Shimadzu 3600 UV-VIR-NIR.

Apparatus: Bruker Advance III 400 MHz, containing a 5 mm multinuclear broad band probe (BBFO+) and z-gradient coil. 30 mg of sample dissolved in 1 mL of d6-DMSO. T= 60 °C. 128 scans for 1D 1H; 32 scans and 128 increments for 2D 1H–

acrylonitrile.


*Processes* **2021**, *9*, 375 Esterification of maleic anhy-

dride grafted onto PHA (through double bond). PHA-g-

> **Cellulose cotton fiber pulp**

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FTIR ATR-FTIR analyses of ungrafted and grafted materials acquired using KBr discs

XRD analyses carried out in a Bruker D8 ADVANCE X-ray apparatus with oper-

[120]

on a Vector 33 Bruker apparatus.

**CellClAc** 

**CellClAc** 

NCHA, 4VP, DA and DAAM grafted by ATRP using CuCl, 2′2′BIPI as catalyst.

NCHA, 4VP, DA and DAAM grafted by ATRP using CuCl, 2′2′BIPI as catalyst.

[122] UV-Visible Apparatus: Shimadzu 3600 UV-VIR-NIR.

[122] UV-Visible Apparatus: Shimadzu 3600 UV-VIR-NIR.

FTIR Apparatus: Perkin Elmer Spectrum One. Solid samples as KBr pellets.


**Lignin** 

**Lignin** 

AA.

AA.

tion)

AA.

AA.

tion)

Insertion of ACX onto lignin to get a RAFT macrocontroller able to polymerize AM and

Insertion of ACX onto lignin to get a RAFT macrocontroller able to polymerize AM and

**Lignin** 

**Lignin** 

Particle size distributions (PSD) measured in an aqueous solution (1 mg/mL) us-

Particle size distributions (PSD) measured in an aqueous solution (1 mg/mL) us-

Particle size distributions (PSD) measured in an aqueous solution (1 mg/mL) us-

Particle size distributions (PSD) measured in an aqueous solution (1 mg/mL) us-

ing a DLS Zeta-sizer (Malvern Instruments). [139]

ing a DLS Zeta-sizer (Malvern Instruments). [139]

ing a DLS Zeta-sizer (Malvern Instruments). [139]

ing a DLS Zeta-sizer (Malvern Instruments). [139]

1H-NMR Apparatus: Bruker 300 Advance; PFB used as internal standard to transform proton intensities into initiator concentration (μmol/(g lignin)).

1H-NMR Apparatus: Bruker 300 Advance; PFB used as internal standard to transform proton intensities into initiator concentration (μmol/(g lignin)).

1H-NMR Apparatus: Bruker 300 Advance; PFB used as internal standard to transform proton intensities into initiator concentration (μmol/(g lignin)). 1H-NMR Apparatus: Bruker 300 Advance; PFB used as internal standard to transform proton intensities into initiator concentration (μmol/(g lignin)).

**Table 9.** Summary of digital imaging and microscopy characterization techniques employed in grafted materials.

**Table 9.** Summary of digital imaging and microscopy characterization techniques employed in grafted materials.

**Table 9.** Summary of digital imaging and microscopy characterization techniques employed in grafted materials.

**Table 9.** Summary of digital imaging and microscopy characterization techniques employed in grafted materials.

Dynamic light scattering (Particle size distribu-

Dynamic light scattering (Particle size distribu-

Dynamic light scattering (Particle size distribution)

Dynamic light scattering (Particle size distribution)

> Insertion of ACX onto lignin to get a RAFT macrocontroller able to polymerize AM and

Insertion of ACX onto lignin to get a RAFT macrocontroller able to polymerize AM and

*Processes* **2021**, *9*, 375 TBD and ε-caprolactone monomers

13C-NMR HSQC

Hemicellulose grafting using

[37] 1H-NMR

Apparatus: Bruker Advance III 400 MHz, containing a 5 mm multinuclear broad band probe (BBFO+) and z-gradient coil. 30 mg of sample dissolved in 1 mL of d6-DMSO. T= 60 °C. 128 scans for 1D 1H; 32 scans and 128 increments for 2D 1H–

**Hemicellulose** 

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FTIR ATR-FTIR analyses of ungrafted and grafted materials acquired using KBr discs

XRD analyses carried out in a Bruker D8 ADVANCE X-ray apparatus with operation at 40 mA and 40 kV. Cu Kα filtered radiation (λ = 0.15418 nm). Scattering

[120]

[121]

on a Vector 33 Bruker apparatus.

**Cellulose cotton fiber pulp**  hydride group).

**Cellulosic filter** 

Radiation-induced graft (RIGCP) copolymerization of

XRD

XRF

to estimate crystallinity index (CI).

XRF analyses performed using a Philips wavelength dispersive equipment X' Unique II, including flow and scintillation (fs) detectors. Qualitative analyses of chelating filter paper-metal complexes were obtained by X-ray fluorescence. FTIR A Nicolet Nexus spectrophotometer with single reflection ATR was used. Range:

4000 to 700 cm−1. Resolution: 4 cm−1; 60 scans.

**papers** 

acrylonitrile.

XRD

angle (2θ): 5° to 50°, 0.02° step.

FTIR FTIR analyses of studied materials (using KBr disks) were obtained using a Per-

XRD analyses of studied materials in an angle range 2θ = 5–50° were obtained in a Shimadzu XRD-610 equipment, with Cu Kα radiation (1.5418°A). Operating conditions: 8 °/min and 1.0 s; 30 kV and 20 mA. Peak height methods were used

kin Elmer-1650 FTIR apparatus.

Esterification of maleic anhydride grafted onto PHA (through double bond). PHA-g-MA grafted onto cellulose cotton fiber pulp (through the an-


polymerization of HEMA

Nitroxide TEMPO insertion

**Cellulose nano-**

**fibrils** 

**Chitosan** 

Embedded polymerizations of N-VP and 4VP. Crosslinking

FTIR Apparatus: AVATAR 370 Thermo Nicolet. Range: 4000 to 500 cm−1, using the KBr

pellet method. Spectral resolution: 4 cm−1.

Apparatus: Bruker Advance D8 equipment (Germany). Diffractograms comprised (2θ) 0.020 imaging; scattering rates: 3 to 800; scanning speeds: 2.0 min−1;

accelerated tension of 40 kV; intensity of 35 mA.

XRD XRD using a Bruker D8 Advance spectrometer. Analyses carried out from 5° to 40° at 4°/min, with a current of 40 mA. Measured property: CI. FTIR Apparatus: Bruker spectrometer, accumulation of 128 scans. Resolution: 4 cm−1.

Range: 4000–400 cm−1; absorbance mode.

[164]

agent: N'N'-MBA

XRD

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**Table 9.** Summary of digital imaging and microscopy characterization techniques employed in grafted materials.

**Lignin** 

**Table 8.** *Cont.*

XPS XPS analyses using Thermo Electron Scientific Instruments were performed us-

ing a 1486.6 eV Al Kα X-ray source.

[124]


**Size exclusion chromatography** 

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It allows determination of molecular weight averages (MW) and molecular weight distributions (MWD) of grafted chains [230], which must be separated from the backbone before carrying out the

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PP/Lignin = 382/333 kW/m2//76 MJ/m2,

Lignin MDT = 398 °C. Lignin-g-IPG MDT > 600 °C.

PP =418°C, PP/Lignin = 472 °C, PP/20 °% Lignin-g-IPG = 479 °C, PP/30 °%

SDTQ600 thermal analyzer; 20 °C/min under nitrogen, from ambient to 600

layer of gold required for samples. [117]

[125,135]

**Lignin** 

Cellulose

Imidazole and POCl3 react in to (1H-imidazol-1-yl)phosphonic group which reacts with lignin

TGA

Lignin-g-IPG = 483 °C.

(DP=1130) Embedded APS and MMA. SEM Apparatus: JSM-6700F scanning microscope. Coating with a thin

°C.

PHRR (kW/m2)//THR (MJ/m2) PP =1350 kW/m2//87.3 MJ/m2, PP/Lignin = 382/333 kW/m2//76 MJ/m2,

FR

57


Microcrystalline

Ring-opening polymerization (ROP) of L-LA

Apparatus: JEM-100CXa TEM at an acceleration voltage of 100

Cotton linter cellu-

lose APS with MMA. SEM

Apparatus: JSM-6700F scanning microscope. Samples coated with gold prior to study. Morphologies and differences between ungrafted and grafted cellulose materials were analyzed.

[115]

*Processes* **2021**, *9*, x FOR PEER REVIEW 40 of 91

**Backbone Grafts Technique Property Measured Application Refs.** 

S4800 FEI SEM; 5 kV accelerating voltage. Comparison of morphologies of char residues after cone calorimeter analyses. PP/Lignin displayed loosely spheroidal structures with C: 86.5 wt.%, O: 13.5 wt.%. PP/30 °% Lignin-g-IPG formed a continuous

Lignin

lignin.

Cellulosic *Grewia optiva* fibers

FAS-H2O2 redox initiation for grafting of MA

and KPS, for polymerization of MA. SEM. The morphologies of ungrafted and grafted fibers were studied

using a SEM apparatus (LEO 435 VP). [110]

Imidazole and POCl3 react to produce (1Himidazol-1-yl) phosphonic, which reacts with

SEM with EDAX and compact spheroidal structure.

Digital photos comparing PP composite sample test probes after

cone calorimeter measurements were obtained.

Digital photo

[125,135]


58

Photo-chemical grafting of PETA without photoinitiator. SEM

Apparatus: JSM-6510 instrument (Joel GmbH, Freising, DE). Samples prepared following standard procedures. Micrographs obtained in SE mode; acceleration voltage: 5 and 10 kV. Purpose:

Analyses of qualitative fracture.

Analyses of qualitative fracture.

Analyses of qualitative fracture.

Analyses of qualitative fracture.

fibres (rayon)

fibres (rayon)

fibres (rayon)

Cellulosic filter pa-

Radiation-induced graft (RIGCP) copolymer-

ization of acrylonitrile. SEM SEM micrographs of samples were obtained on a JEOL-SEM 5400

microscope. [109]

pers

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SEM Apparatus: su1510 (Hitachi Zosen Corporation) operating at 30

kV. Focus: measurement of homogeneity of PMMA composites.

Apparatus: JEM-2100 electron microscope. Operation involves acceleration voltage of 200 kV. Focus: Analysis of morphological

features and distribution of cellulose nanocrystals.

[118]

Cellulose nanocrys-

Macromolecular initiator obtained from BriBuBr and CNC with TEA as catalyst via SI-ATRP with Sty. Material was casted in

> tal (CNC)

PMMA.

Cellulose cotton fi-

Esterification of maleic anhydride grafted onto PHA (through double bond). PHA-g-MA grafted onto cellulose cotton fiber pulp

SEM

Apparatus: Nova Nano SEM 430 (FEI Company); high-resolution field emission with operation at an acceleration voltage of 15 kV. Focus: Morphological analysis of PHA/CF composite films.

[108]

ber pulp

(through the anhydride group).

TEM



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**Table 11.** Summary of chromatographic characterization techniques used for grafted materials. **Backbone Grafts Technique Property Measured Application Refs.**

**Table 11.** Summary of chromatographic characterization techniques used for grafted materials. **Backbone Grafts Technique Property Measured Application Refs.**

**Table 11.** Summary of chromatographic characterization techniques used for grafted materials. **Backbone Grafts Technique Property Measured Application Refs.**

**Table 11.** Summary of chromatographic characterization techniques used for grafted materials. **Backbone Grafts Technique Property Measured Application Refs.**

60



**Cellulose acetate** 

NIPAAM

**Hydroxypropyl cellulose (HPC)**  **Microcrystalline cellulose** 

**Cellulose acetate** 

**Microcrystalline cellulose** 

ROP of L-LA with DMAP in an ionic liquid (AmimCl) to produce Cellulose-*g*-PLLA.

HPLC Apparatus: Agilent 1200 with an XDB-C18 phase column. Eluent: H2O—methanol

(20:80 by vol.), 0.8 mL/min. [116]

ROP of L-LA with DMAP in an ionic liquid (AmimCl) to produce Cellulose-*g*-PLLA.

GPC

200−106 g/mol.

Solvents: DMSO, PDX, DMAc, C3H6O; initiators for grafting and polymerization: CAN, Sn(Oct)2 and BPO.

HPLC Apparatus: Agilent 1200 with an XDB-C18 phase column. Eluent: H2O—methanol

Number average molecular weights (Mn) and dispersity values (Ð) of grafted PMMA extracted from samples of graft copolymer. Apparatus: Agilent 1100 with 3 PSS GPC 8 300 mm, 5 mm, 106, 105, 103 A columns; eluent: THF, 0.8 mL/min, at 20°C. Calibration using polystyrene standards with molecular weights ranging

(20:80 by vol.), 0.8 mL/min. [116]

[111]

GPC

200−106 g/mol.

Solvents: DMSO, PDX, DMAc, C3H6O; initiators for grafting and polymerization: CAN, Sn(Oct)2 and BPO.

Steglich esterification of PABTC over HPC using DCC and DMAP, and grafting of PABTC, with further polymerization of EA and

Number average molecular weights (Mn) and dispersity values (Ð) of grafted PMMA extracted from samples of graft copolymer. Apparatus: Agilent 1100 with 3 PSS GPC 8 300 mm, 5 mm, 106, 105, 103 A columns; eluent: THF, 0.8 mL/min, at 20°C. Calibration using polystyrene standards with molecular weights ranging

SEC MWD by SEC; two PL polar gel M and one PL polar gel 5 mm guard columns; re-

fractive index detector; Eluent: N,N-dimethylformamide/ 0.3 M LiBr, 0.5 mL/min. [108]

[111]


**Table 12.** Summary of characterization techniques based on mechanical properties used for grafted materials.

**Table 12.** Summary of characterization techniques based on mechanical properties used for grafted materials.

**Table 12.** Summary of characterization techniques based on mechanical properties used for grafted materials.

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 

TT s/e values for Lignin-g-PSBMAH (1.5 MPa/220 %), PSBMAH (3.0 MPa/120 %) and epoxy resin prepared from grafted materials (17 MPa/22.5 %). Tensile tests were carried out using a crosshead speed of 20 mm/min at ambient temperature. Samples were casted to obtain films. THF polymer solution samples were dried for 12 h under vacuum at ambient temperature and for 6 h, at 60 °C. Films were cut

TT s/e values for Lignin-g-PSBMAH (1.5 MPa/220 %), PSBMAH (3.0 MPa/120 %) and epoxy resin prepared from grafted materials (17 MPa/22.5 %). Tensile tests were carried out using a crosshead speed of 20 mm/min at ambient temperature. Samples were casted to obtain films. THF polymer solution samples were dried for 12 h under vacuum at ambient temperature and for 6 h, at 60 °C. Films were cut

TT s/e values for Lignin-g-PSBMAH (1.5 MPa/220 %), PSBMAH (3.0 MPa/120 %) and epoxy resin prepared from grafted materials (17 MPa/22.5 %). Tensile tests were carried out using a crosshead speed of 20 mm/min at ambient temperature. Samples were casted to obtain films. THF polymer solution samples were dried for 12 h under vacuum at ambient temperature and for 6 h, at 60 °C. Films were cut

[134]

[134]

[134]

into dog-bone tensile samples of 20 mm length and 5 mm width.

into dog-bone tensile samples of 20 mm length and 5 mm width.

into dog-bone tensile samples of 20 mm length and 5 mm width.

Lignin-RAFT macro-controller

Lignin-RAFT macro-controller

Lignin-RAFT macro-controller MAEO.

MAEO.

MAEO.

Poly(soybean oil methacrylate) derivatives. PSBMA, PSBMAH, PSB-

Poly(soybean oil methacrylate) derivatives. PSBMA, PSBMAH, PSB-

Poly(soybean oil methacrylate) derivatives. PSBMA, PSBMAH, PSB-

Tensile strength

Tensile strength

Tensile strength


(through the anhydride

(through the anhydride

group).

group).

group).

Hemicellulose

Hemicellulose

Hemicellulose

Hemicellulose

Hemicellulose grafting using TBD and ɛ-caprolactone monomer

Hemicellulose grafting using TBD and ɛ-caprolactone monomer

Hemicellulose grafting using TBD and ɛ-caprolactone monomer

Hemicellulose grafting using TBD and ɛ-caprolactone monomer

Tensile strength

Tensile strength

Tensile strength

Tensile strength elongation at break (5 repeats).

elongation at break (5 repeats).

elongation at break (5 repeats).

elongation at break (5 repeats).

Apparatus: Shimadzu Autograph AG-500A. Method: ISO 527-2. Specimen size: 35 × 4 × 0.3 mm. Tests carried out at ambient conditions; 10 mm/min, 12 mm distance between grips. Properties measured: ultimate strength, Young's modulus, and

Apparatus: Shimadzu Autograph AG-500A. Method: ISO 527-2. Specimen size: 35 × 4 × 0.3 mm. Tests carried out at ambient conditions; 10 mm/min, 12 mm distance between grips. Properties measured: ultimate strength, Young's modulus, and

Apparatus: Shimadzu Autograph AG-500A. Method: ISO 527-2. Specimen size: 35 × 4 × 0.3 mm. Tests carried out at ambient conditions; 10 mm/min, 12 mm distance between grips. Properties measured: ultimate strength, Young's modulus, and

Apparatus: Shimadzu Autograph AG-500A. Method: ISO 527-2. Specimen size: 35 × 4 × 0.3 mm. Tests carried out at ambient conditions; 10 mm/min, 12 mm distance between grips. Properties measured: ultimate strength, Young's modulus, and [37]

[37]

[37]

[37]

*Processes* **2021**, *9*, 375

AM and AA.

**Lignin** 

Insertion of ACX onto lignin to produce a RAFT macrocontroller which polymerizes

GPC Apparatus: Waters Alliance 2695; eluent: aqueous solution of 0.1 M sodium phos-

phate buffer and 0.01% NaN3, at ambient temperature, 1 mL/min. [139]

**Hemicellulose** 

omers.

Hemicellulose grafting using TBD and e-caprolactone mon-

GPC

Apparatus: Malvern Viscotek HT GPC 350; refractive index (RI) and viscometer detectors. PSS-GRAM columns covering a range of 100–1000,000 g/mol. Eluent: DMSO at 80 °C. Universal calibration using pullulan polysaccharide standards.

[37]

*Processes* **2021**, *9*, x FOR PEER REVIEW 45 of 91

Esterification of maleic anhydride grafted over PHA (through double

Cellulosic *Grewia optiva* fibers

Cellulose nano-

Tensile strength

The mechanical properties of nanocomposites were investigated through breaking

strength and elongation at break tests. [118]

Macromolecular initiator obtained from the reaction between Br-iBuBr and CNC using TEA as catalyst, via SI-ATRP with Sty. Material was casted in PMMA.

> crystal (CNC)

FAS-H2O2 redox initiation for grafting of MA and KPS, followed by polymerization of MA.

Swell index Swelling of raw and grafted fibers in different solvents (DMF, water, methanol, and

isobutyl alcohol) was measured. [110]

*Processes* **2021**, *9*, x FOR PEER REVIEW 46 of 91


tions.

tions.

tions.

**Table 13.** Summary of biological, functional, and compositional characterization techniques employed in grafted materials.

**Table 13.** Summary of biological, functional, and compositional characterization techniques employed in grafted materials.

**Table 13.** Summary of biological, functional, and compositional characterization techniques employed in grafted materials.

**Table 13.** Summary of biological, functional, and compositional characterization techniques employed in grafted materials.

proceeded until breakage or reaching runout conditions.

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 

**Backbone Grafts Technique Property Measured Application Refs.** 


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those of intestinal fluid (pH 7.40) at 37 °C. 2 mL samples were taken at predetermined times, and analyzed at lmax= 245 nm for vitamin C.

A solution of grafted material (60.0 mg) and vitamin C (60.0 mg) in 2 mL of PBS was prepared and then transferred to a dialysis bag. Dialysis against 1 L distilled water for 24 h (water refreshment after 12 h) followed. Afterwards, the dialysis bag was immersed into a 400 mL phosphate buffer solution, at conditions similar to those of intestinal fluid (pH 7.40) at 37 °C. 2 mL samples were taken at predetermined times, and analyzed at lmax= 245 nm for vitamin C.

samples were taken at predetermined times, and analyzed at lmax= 245 nm for vitamin C.

**Microcrystalline cellulose** 

ROP of L-LA with DMAP in an ionic liquid (AmimCl) to produce Cellulose-*g*-PLLA

Load and controlled re-

[116]

lease

65


Biodegradation test

Biodegradation test

**CellClAc** 

**CellClAc** NCHA, and DAAM

grafted by atom transfer radical polymerization using 2′as cata-

NCHA, 4VP, DA and DAAM grafted by atom transfer radical polymerization (ATRP) using CuCl, 2′2′BIPI as cata-

NCHA, 4VP, DA and DAAM grafted by atom transfer radical polymerization (ATRP) using CuCl, 2′2′BIPI as cata-

**CellClAc** 

**CellClAc** 

lyst.

lyst.

lyst.

Electrical conductivity

lyst. Elemental Elemental analyses carried in Leco CHNS-

tor.

Electrical conductivity with a Keithley 6517A electrometer. was the that as tor.

tor.

tor.

Electrical conductivity

Electrical conductivity

NCHA, 4VP, DA and DAAM grafted by atom transfer radical polymerization (ATRP) using CuCl, 2′2′BIPI as cata-

Elemental analysis Elemental analyses carried out in a Leco CHNS-932 apparatus.

Electrical conductivity determined with a Keithley 6517A electrometer. Cell-g-4VP was the only material that behaved as semiconduc-

Electrical conductivity determined with a Keithley 6517A electrometer. Cell-g-4VP was the only material that behaved as semiconduc-

932 apparatus. [122] Electrical conductivity

Electrical conductivity determined with a Keithley 6517A electrometer. Cell-g-4VP was the only material that behaved as semiconduc-

Elemental analysis Elemental analyses carried out in a Leco CHNS-

Elemental analysis Elemental analyses carried out in a Leco CHNS-

932 apparatus.

932 apparatus.

[122]

[122]

[122]

mand (BOD) measurements were obtained un-

mand (BOD) measurements were un-

Method: ISO 14851. Biochemical Oxygen Demand (BOD) measurements were obtained un-

der aerobic conditions.

Biodegradation test 14851. Biochemical De-

der aerobic conditions.

der

Biodegradation test Method: ISO 14851. Biochemical Oxygen Demand (BOD)

measurements were obtained under aerobic conditions.

der aerobic conditions.


*Processes* **2021**, *9*, 375 **Hemicellulose** 

Hemicellulose grafting using TBD and ε-caprolactone

[37]

Contact angle

100–00.

Measurements carried out using an NRL Contact Angle Goniometer by Rame-Hart, model

monomers.

Biodegradation test

Method: ISO 14851. Biochemical Oxygen Demand (BOD) measurements were obtained un-

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**Cellulose cotton fiber pulp** 

Contact angle (hydrophobicity)

group).

**Cellulosic filter papers** 

Radiation-induced graft (RIGCP) copolymerization of

acrylonitrile.

were estimated from these data.

Chelating rare elements Chelation of uranium, thorium, and lanthanides

by the batch procedure took place. [121]

Esterification of maleic anhydride grafted onto PHA (through double bonds). PHA-g-MA grafted onto cellulose cotton fiber pulp (through the anhydride

Surface roughness Measurement of surface roughness accom-

plished using an L&M CE165 PPS tester.

Surface hydrophilicity was analyzed by contact angle measurements. Tests carried out at ambient conditions using a Dataphysics OCA40 Micro instrument. Surface free energy parameters

[120]

MBA

release

Load and controlled re-

was ground to fine power followed by immersion of a known amount of it into 0.1 L of HCl aqueous solution for 24 h under magnetic stirring. Then, the solution was filtered and used to determine the absorbance (A) of the drug contained in it using a Perkin Elmer Lambda 35 apparatus at 280 nm. Release profiles of the model drug (doxocyline) from the drug-loaded polymers were determined in distilled water (pH = 1.5) and in buffer solutions (pH = 6.8). All the

absorbance (A) of the drug contained in it using a Perkin Elmer Lambda 35 apparatus at 280 nm. Release profiles of the model drug (doxocyline) from the drug-loaded polymers were determined in distilled water (pH = 1.5) and in buffer solutions (pH = 6.8). All the studies were

paratus at 280 nm. Release profiles of the model drug (doxocyline) from the drug-loaded polymers were determined in distilled water (pH = 1.5) and in buffer solutions (pH = 6.8). All the

lease

studies were carried out in triplicate.

carried out in triplicate.

studies were carried out in triplicate.


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freezing method. Samples produced using the direct freezing method exhibited higher resistiv-

ity values.

direct freezing method exhibited higher resistiv-

direct freezing method exhibited higher resistiv-

direct freezing method exhibited higher resistiv-

ity values.

ity values.

to produce a RAFT macro- Surface tension Apparatus: De Nouy ring-type tensiometer

ity values.

ity values.

to produce a RAFT macro- Surface tension Apparatus: De Nouy ring-type tensiometer

to produce a RAFT macro- Surface tension Apparatus: De Nouy ring-type tensiometer

to produce a RAFT macro- Surface tension Apparatus: De Nouy ring-type tensiometer

to produce a RAFT macro- Surface tension Apparatus: De Nouy ring-type tensiometer

(Krüss), at 25 °C. [139]

(Krüss), at 25 °C. [139]

(Krüss), at 25 °C. [139]

(Krüss), at 25 °C. [139]

(Krüss), at 25 °C. [139]

**Lignin** Insertion of ACX onto lignin

**Lignin** Insertion of ACX onto lignin

**Lignin** Insertion of ACX onto lignin

**Lignin** Insertion of ACX onto lignin

**Lignin** Insertion of ACX onto lignin



[231]

[232]

[233]

twin-screw extruder (TSE).

PE CTP by FRP in melt, in a

twin-screw extruder (TSE).

(PGMA)

Poly(maleic anhydride)

(PMAH)

model consisting of plug flow and "axial dispersion" reactor cells. Coupling of reaction kinetics to flow equations in a twin-screw extruder.

agreement with experimental data.

Satisfactory agreement between

calculated and experimental data. [235]

[234]

*Processes* **2021**, *9*, 375



71



72



[249]

[250,251]

[252]

[253]



74



75

**Table 16.** Symbols of application fields.

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Flame retardancy, additives for flame retardancy in polymer blends,

Flame retardancy, additives for flame retardancy in polymer blends,

Flame retardancy, additives for flame retardancy in polymer blends,

Adhesives, polymer networks, crosslinked polymers, gels.

Adhesives, polymer networks, crosslinked polymers, gels.

Adhesives, polymer networks, crosslinked polymers, gels.

Polymer composites and blends, by extrusion, casting or co-precipita-

Polymer composites and blends, by extrusion, casting or co-precipita-

Polymer composites and blends, by extrusion, casting or co-precipita-

Controlled release of drugs and chemicals.

Controlled release of drugs and chemicals.

Controlled release of drugs and chemicals.

tion.

tion.

tion.

thermal resistance materials.

thermal resistance materials.

thermal resistance materials.

Antimicrobial applications.

Antimicrobial applications.

Antimicrobial applications.

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Green chemistry and innovative processes.

Green chemistry and innovative processes.

Green chemistry and innovative processes.

Green chemistry and innovative processes.

Green chemistry and innovative processes.


**Table 16.** *Cont.*

Electronic materials, electrical properties, and conjugated polymers.

Electronic materials, electrical properties, and conjugated polymers.

Electronic materials, electrical properties, and conjugated polymers.

Electronic materials, electrical properties, and conjugated polymers.

Electronic materials, electrical properties, and conjugated polymers.

Surface modification, hydrophilic or hydrophobic surfaces.

Surface modification, hydrophilic or hydrophobic surfaces.

Surface modification, hydrophilic or hydrophobic surfaces.

Surface modification, hydrophilic or hydrophobic surfaces.

Surface modification, hydrophilic or hydrophobic surfaces.

Mechanical properties improvement, micro and nano reinforcement.

Application in polyolefins, polyethylene, polypropylene.

Aerogels, light, or porous materials.

FTIR Fourier transformed mid-infrared spectroscopy.

**Table 17.** Abbreviations used for characterization techniques.

ATR Attenuated total reflection.

1H-NMR Proton nuclear magnetic resonance. 13C-NMR Carbon nuclear magnetic resonance.

DMA Dynamical mechanical analysis. GPC Gel permeation chromatography. TGA Thermogravimetric analysis. DSC Differential scanning calorimetry.

XPS X-ray photoelectron spectroscopy.

WAXD Wide Angle X-ray Scattering.

EDAX Energy-dispersive X-ray analysis/spectroscopy.

**Table 18.** Abbreviations of properties and variables measured by characterization techniques. **Technique Abbreviation Explanation Units**  Chromatography MWD Molecular weight distribution of polymers. -

Mechanical σ Maximum stress measured in tensile test. MPa

Mn Number average molecular weight. g/gmol

Tg Glass transition temperature. °C MDT Maximum degradation temperature. °C MFI Melt flow index. g/10 min THR Total heat release. MJ/m2 PHRR Peak heat release rate. kW/m2

**Abbreviation Meaning** 

TT Tensile test.

FR Flame retardancy.

XRF X-ray fluorescence.

Thermal

Thermal

Thermal

Thermal

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#### **Table 16.** *Cont.*

Chelating properties, membranes, effluent remediation.

Chelating properties, membranes, effluent remediation.

Chelating properties, membranes, effluent remediation.

#### **Table 17.** Abbreviations used for characterization techniques. **Table 17.** Abbreviations used for characterization techniques. **Table 17.** Abbreviations used for characterization techniques. **Table 17.** Abbreviations used for characterization techniques.


Mn Number average molecular weight. g/gmol

Mn Number average molecular weight. g/gmol

Tg Glass transition temperature. °C MDT Maximum degradation temperature. °C MFI Melt flow index. g/10 min THR Total heat release. MJ/m2 PHRR Peak heat release rate. kW/m2

Tg Glass transition temperature. °C MDT Maximum degradation temperature. °C MFI Melt flow index. g/10 min THR Total heat release. MJ/m2 PHRR Peak heat release rate. kW/m2

Tg Glass transition temperature. °C MDT Maximum degradation temperature. °C MFI Melt flow index. g/10 min THR Total heat release. MJ/m2 PHRR Peak heat release rate. kW/m2

Mechanical σ Maximum stress measured in tensile test. MPa

Mechanical σ Maximum stress measured in tensile test. MPa

Mechanical σ Maximum stress measured in tensile test. MPa


**Table 18.** Abbreviations of properties and variables measured by characterization techniques.

**Table 19.** Abbreviations and formulae of some chemical compounds and materials used. ɛ Maximum elongation observed in tensile test. % ɛ Maximum elongation observed in tensile test. % ɛ Maximum elongation observed in tensile test. % **Table 19.** Abbreviations and formulae of some chemical compounds and materials used. **Table 19.** Abbreviations and formulae of some chemical compounds and materials used. **Abbreviation Compound Chemical Structure Ref.** 

ɛ Maximum elongation observed in tensile test. %

**Table 19.** Abbreviations and formulae of some chemical compounds and materials used.


PE Polyethylene. [135]

PE Polyethylene. [135]

PE Polyethylene. [135]

DCC Dicyclohexylcarbodiimide. [108,165]

DCC Dicyclohexylcarbodiimide. [108,165]

DCC Dicyclohexylcarbodiimide. [108,165]

DCC Dicyclohexylcarbodiimide. [108,165]

DCC Dicyclohexylcarbodiimide. [108,165]

DCC Dicyclohexylcarbodiimide. [108,165]

DMAP 4-Dimethylaminopyridine. [108,116,165]

DMAP 4-Dimethylaminopyridine. [108,116,165]

DMAP 4-Dimethylaminopyridine. [108,116,165]

DMAP 4-Dimethylaminopyridine. [108,116,165]

DMAP 4-Dimethylaminopyridine. [108,116,165]

methacrylate. [134]

methacrylate. [134]

methacrylate. [134]

methacrylate. [134]

methacrylate. [134]

methacrylate. [134]

SBMA (*E*)-2-(N-methyloctadec-9-enamido)ethyl

SBMA (*E*)-2-(N-methyloctadec-9-enamido)ethyl

SBMA (*E*)-2-(N-methyloctadec-9-enamido)ethyl

SBMA (*E*)-2-(N-methyloctadec-9-enamido)ethyl

SBMA (*E*)-2-(N-methyloctadec-9-enamido)ethyl

SBMA (*E*)-2-(N-methyloctadec-9-enamido)ethyl

DMF Dimethylformamide.

DMF Dimethylformamide.

DMF Dimethylformamide.

"P" Before the name or abbreviation of a mono-

"B-g-C" Means "C" chains grafted to "B" backbone.

"P" Before the name or abbreviation of a mono-

mer means polymer of that monomer.

"B-g-C" Means "C" chains grafted to "B" backbone.

mer means polymer of that monomer.

mer means polymer of that monomer.

"P" Before the name or abbreviation of a mono-

"B-g-C" Means "C" chains grafted to "B" backbone.


#### **Table 19.** *Cont.* PE Polyethylene. [135] PE Polyethylene. [135] PE Polyethylene. [135]

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**Table 19.** Abbreviations and formulae of some chemical compounds and materials used.

**Table 19.** Abbreviations and formulae of some chemical compounds and materials used.

**Abbreviation Compound Chemical Structure Ref.** 

THF Tetrahydrofuran. [17,18]

**Abbreviation Compound Chemical Structure Ref.** 

*Processes* **2021**, *9*, x FOR PEER REVIEW 67 of 91

**Table 19.** Abbreviations and formulae of some chemical compounds and materials used.

**Abbreviation Compound Chemical Structure Ref.** 

THF Tetrahydrofuran. [17,18]

DMSO Dimethyl Sulfoxide. [37,111]

PDX 1,4-dioxane. [111,140,142,1

PP Polypropylene. [135]

THF Tetrahydrofuran. [17,18]

DMSO Dimethyl Sulfoxide. [37,111]

DMSO Dimethyl Sulfoxide. [37,111]

PDX 1,4-dioxane. [111,140,142,1

PP Polypropylene. [135]

PDX 1,4-dioxane. [111,140,142,1

PP Polypropylene. [135]

ɛ Maximum elongation observed in tensile test. %

ɛ Maximum elongation observed in tensile test. %

ɛ Maximum elongation observed in tensile test. %

[121,125,139,1 41,144,146,14 7,151,152,165]

[121,125,139,1 41,144,146,14 7,151,152,165]

[121,125,139,1 41,144,146,14 7,151,152,165]

50]

50]

50]

Imidazole. [125,135]

Imidazole. [125,135]

Imidazole. [125,135]

Imidazole. [125,135]

IPG (1H-imidazol-1-yl) phosphonic group. [125,135]

N'N'-MBA N'N'-methylenebisacrylamide. [98,164]

IPG (1H-imidazol-1-yl) phosphonic group. [125,135]

N'N'-MBA N'N'-methylenebisacrylamide. [98,164]

Imidazole. [125,135]

IPG (1H-imidazol-1-yl) phosphonic group. [125,135]

IPG (1H-imidazol-1-yl) phosphonic group. [125,135]

IPG (1H-imidazol-1-yl) phosphonic group. [125,135]

N'N'-MBA N'N'-methylenebisacrylamide. [98,164]

N'N'-MBA N'N'-methylenebisacrylamide. [98,164]

N'N'-MBA N'N'-methylenebisacrylamide. [98,164]

NIPAAM N-isopropylacrylamide.

NIPAAM N-isopropylacrylamide.

NIPAAM N-isopropylacrylamide.

NIPAAM N-isopropylacrylamide.

NIPAAM N-isopropylacrylamide.

PNIPAAM Poly(N-isopropylacrylamide).

PNIPAAM Poly(N-isopropylacrylamide).

PNIPAAM Poly(N-isopropylacrylamide).

PNIPAAM Poly(N-isopropylacrylamide).

PNIPAAM Poly(N-isopropylacrylamide).

4-cyano-4-(phenylcarbonothioylthio) penta-

4-cyano-4-(phenylcarbonothioylthio) penta-

4-cyano-4-(phenylcarbonothioylthio) penta-

SBMAH (*E*)-3-(octadec-9-enamido)propyl methacry-

SBMAH (*E*)-3-(octadec-9-enamido)propyl methacry-

SBMAH (*E*)-3-(octadec-9-enamido)propyl methacry-

SBMAEO 2-(N-methyl-8-(3-octyloxiran-2-yl)octan-

SBMAEO 2-(N-methyl-8-(3-octyloxiran-2-yl)octan-

SBMAEO 2-(N-methyl-8-(3-octyloxiran-2-yl)octan-

*Processes* **2021**, *9*, x FOR PEER REVIEW 68 of 91

late. [134]

late. [134]

late. [134]

amido)ethyl methacrylate. [134]

noic acid. [134]

*Processes* **2021**, *9*, x FOR PEER REVIEW 68 of 91

amido)ethyl methacrylate. [134]

noic acid. [134]

POCl3 Phosphoryl trichloride. [125,135]

*Processes* **2021**, *9*, x FOR PEER REVIEW 68 of 91

amido)ethyl methacrylate. [134]

noic acid. [134]

POCl3 Phosphoryl trichloride. [125,135]

POCl3 Phosphoryl trichloride. [125,135]


#### **Table 19.** *Cont.*

PABTC Propionic acidyl butyl trithiocarbonate. [108]

PABTC Propionic acidyl butyl trithiocarbonate. [108]

PABTC Propionic acidyl butyl trithiocarbonate. [108]

PABTC Propionic acidyl butyl trithiocarbonate. [108]

PABTC Propionic acidyl butyl trithiocarbonate. [108]

[108,138,140,1 41,143,145,16

5]

[108,138,140,1 41,143,145,16

5]

[108,138,140,1 41,143,145,16

[108,138,140,1 41,143,145,16

[108,138,140,1 41,143,145,16

[108,138,140,1 41,143,145,16

5]

[108,138,140,1 41,143,145,16

5]

[108,138,140,1 41,143,145,16

[108,138,140,1 41,143,145,16

[108,138,140,1 41,143,145,16

5]

5]

5]

5]

5]

5]

MMA Methyl methacrylate.

PMMA Poly(methyl methacrylate).

MMA Methyl methacrylate.

MMA Methyl methacrylate.

PMMA Poly(methyl methacrylate).

PMMA Poly(methyl methacrylate).

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N-VP N-vinyl pyrrolidone. [99,164]

Co(acac)3 Cobaltacetylacetonate complex. [99,103]

AcN Acrylonitrile. [107,121]

EA Ethyl acrylate. [107,108]

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N-VP N-vinyl pyrrolidone. [99,164]

N-VP N-vinyl pyrrolidone. [99,164]

Co(acac)3 Cobaltacetylacetonate complex. [99,103]

Co(acac)3 Cobaltacetylacetonate complex. [99,103]

AcN Acrylonitrile. [107,121]

AcN Acrylonitrile. [107,121]

EA Ethyl acrylate. [107,108]

EA Ethyl acrylate. [107,108]

[58,107,111,11 7,140,144,146,

[58,107,111,11 7,140,144,146,

[58,107,111,11 7,140,144,146,

149]

149]

[58,107,111,11 7,140,144,146,

[58,107,111,11 7,140,144,146,

[58,107,111,11 7,140,144,146,

149]

149]

149]

149]


#### FAS Ferrous ammonium sulphate. (NH4)2Fe(SO4)2 6H2O [110] FAS Ferrous ammonium sulphate. (NH4)2Fe(SO4)2 6H2O [110] FAS Ferrous ammonium sulphate. (NH4)2Fe(SO4)2 6H2O [110] 82

**Ce** 

**Ce** 

**Ce** 

**Ce** 

**Ce** 

MA Methyl acrylate. [110]

MA Methyl acrylate. [110]

FAS Ferrous ammonium sulphate. (NH4)2Fe(SO4)2 6H2O [110]

KPS Potassium persulphate. [110]

CAN Ceric ammonium nitrate. [111]

KPS Potassium persulphate. [110]

KPS Potassium persulphate. [110]

CAN Ceric ammonium nitrate. [111]

CAN Ceric ammonium nitrate. [111]

FAS Ferrous ammonium sulphate. (NH4)2Fe(SO4)2 6H2O [110]

KPS Potassium persulphate. [110]

CAN Ceric ammonium nitrate. [111]

KPS Potassium persulphate. [110]

CAN Ceric ammonium nitrate. [111]


#### **Table 19.** *Cont.* MA Methyl acrylate. [110] MA Methyl acrylate. [110]

46,147]

46,147]

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HPC Hydroxypropyl cellulose. [108]

DMAc Dimethylacetamide. [108]

CellClAc Cellulose chloroacetate. [109,122]

<sup>2</sup>′2′BIPI 2,2′-bipyridine. [109,122,140,1

*Processes* **2021**, *9*, x FOR PEER REVIEW 70 of 91

HPC Hydroxypropyl cellulose. [108]

DMAc Dimethylacetamide. [108]

CellClAc Cellulose chloroacetate. [109,122]

4NPA N-(4-nitrophenyl) acrylamide. [109]

<sup>2</sup>′2′BIPI 2,2′-bipyridine. [109,122,140,1

4NPA N-(4-nitrophenyl) acrylamide. [109]

MTC-b-CD Monochlorotriazinyl-β-cyclodextrin. [113,114]

MTC-b-CD Monochlorotriazinyl-β-cyclodextrin. [113,114]

MTC-b-CD Monochlorotriazinyl-β-cyclodextrin. [113,114]

MTC-b-CD Monochlorotriazinyl-β-cyclodextrin. [113,114]

APS Ammonium persulfate. [115,117]

APS Ammonium persulfate. [115,117]

AmimCl 1-allyl-3-methylimidazolium chloride. [116]

AmimCl 1-allyl-3-methylimidazolium chloride. [116]

PBS Phosphate-buffered saline solutions. [116]

PBS Phosphate-buffered saline solutions. [116]

APS Ammonium persulfate. [115,117]

APS Ammonium persulfate. [115,117]

AmimCl 1-allyl-3-methylimidazolium chloride. [116]

AmimCl 1-allyl-3-methylimidazolium chloride. [116]

PBS Phosphate-buffered saline solutions. [116]

PBS Phosphate-buffered saline solutions. [116]


#### **Table 19.** *Cont.*

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BPO Benzoyl peroxide. [111]

Sn(Oct)2 Tin(II) 2-ethyl hexanoate. [111]

NCA N-cyclohexylacrylamide. [112]

AgNPs Silver nanoparticles. Ag [113]

*Processes* **2021**, *9*, x FOR PEER REVIEW 71 of 91

BPO Benzoyl peroxide. [111]

BPO Benzoyl peroxide. [111]

Sn(Oct)2 Tin(II) 2-ethyl hexanoate. [111]

NCA N-cyclohexylacrylamide. [112]

AgNPs Silver nanoparticles. Ag [113]

b-CD β-cyclodextrin. [113,114]

*Processes* **2021**, *9*, x FOR PEER REVIEW 71 of 91

Sn(Oct)2 Tin(II) 2-ethyl hexanoate. [111]

NCA N-cyclohexylacrylamide. [112]

AgNPs Silver nanoparticles. Ag [113]

b-CD β-cyclodextrin. [113,114]

PS or PSty Polystyrene. [58,118,140,14

PS or PSty Polystyrene. [58,118,140,14

PS or PSty Polystyrene. [58,118,140,14

PS or PSty Polystyrene. [58,118,140,14

STY or Sty Styrene. [58,118,140,14

STY or Sty Styrene. [58,118,140,14

STY or Sty Styrene. [58,118,140,14

TEA Triethylamine. [118]

TEA Triethylamine. [118]

TEA Triethylamine. [118]

TEA Triethylamine. [118]

6,147,149]

6,147,149]

6,147,149]

6,147,149]

6,147,149]

6,147,149]

6,147,149]

6,147,149]

Poly(L-lactide).

Poly(L-lactide).

Poly(L-lactide).

Poly(D-lactide).

L-lactide. D-lactide.

L-lactide. D-lactide.

L-lactide. D-lactide.

L-LA D-LA

L-LA D-LA

L-LA D-LA

PLLA

PLLA

PLLA

PDLA

PDLA

PDLA

#### **Table 19.** *Cont.*

[116,119,157,1

[116,119,157,1

[116,119,157,1

[116,119,157,1

[116,119,157,1

[116,119,157,1

59]

59]

59]

59]

59]

59]

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DMAc N,N-dimethyl acetamide. [111,117]

DMAc N,N-dimethyl acetamide. [111,117]

DMAc N,N-dimethyl acetamide. [111,117]

Br-iBuBr 2-Bromoisobutyryl bromide. [118]

Br-iBuBr 2-Bromoisobutyryl bromide. [118]

Br-iBuBr 2-Bromoisobutyryl bromide. [118]

1,162]

1,162]

1,162]

1,162]

1,162]

1,162]

1,162]

1,162]

1,162]

1,162]

NCHA N-cyclohexylacrylamide. [122]

CL ε-Caprolactone.. [37,158,159,16

CL ε-Caprolactone.. [37,158,159,16

CL ε-Caprolactone.. [37,158,159,16

PCL Poly-(ε-caprolactone). [37,158,159,16

PCL Poly-(ε-caprolactone). [37,158,159,16

PCL Poly-(ε-caprolactone). [37,158,159,16

PCL Poly-(ε-caprolactone). [37,158,159,16

NCHA N-cyclohexylacrylamide. [122]

CL ε-Caprolactone.. [37,158,159,16

CL ε-Caprolactone.. [37,158,159,16

PCL Poly-(ε-caprolactone). [37,158,159,16

PMDETA N, N, N', N', N"-Pentamethyldiethylenetri-

PMDETA N, N, N', N', N"-Pentamethyldiethylenetri-

PHA-g-MA Poly(hydroxyalkanoate-grafted-maleic an-

PHA-g-MA Poly(hydroxyalkanoate-grafted-maleic an-

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PHA Polyhydroxyalkanoate. [120]

TBD 1,5,7- triazabicyclodecene [4.4.0]. [37]

NCHA N-cyclohexylacrylamide. [122]

amine. [118,140,146]

PHA Polyhydroxyalkanoate. [120]

amine. [118,140,146]

*Processes* **2021**, *9*, x FOR PEER REVIEW 73 of 91

hydride). [120]

TBD 1,5,7- triazabicyclodecene [4.4.0]. [37]

NCHA N-cyclohexylacrylamide. [122]

hydride). [120]


#### **Table 19.** *Cont.*

DMAEMA 2-dimethylaminoethyl methacrylate. [138,150]

DMAEMA 2-dimethylaminoethyl methacrylate. [138,150]

BA Butyl acrylate. [138]

EG Ethylene glycol. [138]

BA Butyl acrylate. [138]

EG Ethylene glycol. [138]

EG Ethylene glycol. [138]

BA Butyl acrylate. [138]

EG Ethylene glycol. [138]

EG Ethylene glycol. [138]

BA Butyl acrylate. [138]

EG Ethylene glycol. [138]

BA Butyl acrylate. [138]

EG Ethylene glycol. [138]


#### **Table 19.** *Cont.*

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4VP 4-vinylpyridine. [122,164]

DAAM Diacetone acrylamide. [122]

DA Diallylamine. [122]

PETA Pentaerythritol triacrylate. [123]

TEMPO TEMPO nitroxide. [124]

HEMA 2-hydroxyethyl methacrylate. [124]

DMAEMA 2-dimethylaminoethyl methacrylate. [138,150]

4VP 4-vinylpyridine. [122,164]

DAAM Diacetone acrylamide. [122]

DA Diallylamine. [122]

PETA Pentaerythritol triacrylate. [123]

TEMPO TEMPO nitroxide. [124]

HEMA 2-hydroxyethyl methacrylate. [124]

DMAEMA 2-dimethylaminoethyl methacrylate. [138,150]

Syringyl methacrylate. [140]

Syringyl methacrylate. [140]

Syringyl methacrylate. [140]

Syringyl methacrylate. [140]

Syringyl methacrylate. [140]

Syringyl methacrylate. [140]

CuBr/HMTETA 1,1,4,7,10,10-Hexamethyltriethylenetetra-

PEG-A Poly(ethylene glycol) acrylate.

CuBr/HMTETA 1,1,4,7,10,10-Hexamethyltriethylenetetra-

CuBr/HMTETA 1,1,4,7,10,10-Hexamethyltriethylenetetra-

PEG-A Poly(ethylene glycol) acrylate.

CuBr/HMTETA 1,1,4,7,10,10-Hexamethyltriethylenetetra-

PEG-A Poly(ethylene glycol) acrylate.

PEG-A Poly(ethylene glycol) acrylate.

PEG-A Poly(ethylene glycol) acrylate.

#### **Table 19.** *Cont.*

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AM Acrylamide. [58,138,139,15

AA Acrylic Acid. [58,138,139]

ACX Acyl chloride xanthate. [139,153]

LMA Lauryl methacrylate. [140]

Guaiacol. [140]

1,153]

n = 9 [140,143]

n = 9 [140,143]

mine Cu(I)Br complex. [140,143,150]

n = 9 [140,143]

n = 9 [140,143]

n = 9 [140,143]


[140,141,146,1

47]

*Processes* **2021**, *9*, x FOR PEER REVIEW 76 of 91

4-propylsyringol. [140]

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4-propylsyringol. [140]

4-propylguaiacol. [140]

4-propylguaiacol. [140]

Ferulic acid. [140]

Ferulic acid. [140]

Isorbide. [140]

Isorbide. [140]

PBMA Poly(butyl methacrylate). [140,144]

PBMA Poly(butyl methacrylate). [140,144]

PBMA Poly(butyl methacrylate). [140,144]

PBMA Poly(butyl methacrylate). [140,144]

PEGMA Poly(ethylene glycol) methacrylate. [140,148]

PEGMA Poly(ethylene glycol) methacrylate. [140,148]

PEGMA Poly(ethylene glycol) methacrylate. [140,148]

PEGMA Poly(ethylene glycol) methacrylate. [140,148]

DMC [2-(Methacryloyloxy)ethyl] trimethyl-am-

DMC [2-(Methacryloyloxy)ethyl] trimethyl-am-

DMC [2-(Methacryloyloxy)ethyl] trimethyl-am-

DMC [2-(Methacryloyloxy)ethyl] trimethyl-am-

DMC [2-(Methacryloyloxy)ethyl] trimethyl-am-

PPG-A Poly(propylen glycol) acrylate.

PPG-A Poly(propylen glycol) acrylate.


#### **Table 19.** *Cont.* BMA Butyl methacrylate. [140,144]

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DAEA Dehydroabietic ethyl acrylate. [140,142]

DAEA Dehydroabietic ethyl acrylate. [140,142]

PDAEA Poly(dehydroabietic ethyl acrylate). [140,142]

PDAEA Poly(dehydroabietic ethyl acrylate). [140,142]

BMA Butyl methacrylate. [140,144]

n = 5 [140,143]

n = 5 [140,143]

HONB N-Hydroxy-5-norbornene-2,3-dicarboxylic. [154]

HONB N-Hydroxy-5-norbornene-2,3-dicarboxylic. [154]

monium chloride. [154]

HONB N-Hydroxy-5-norbornene-2,3-dicarboxylic. [154]

monium chloride. [154]

monium chloride. [154]

HONB N-Hydroxy-5-norbornene-2,3-dicarboxylic. [154]

HONB N-Hydroxy-5-norbornene-2,3-dicarboxylic. [154]


#### **Table 19.** *Cont.*

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*Processes* **2021**, *9*, x FOR PEER REVIEW 78 of 91

PPh3 Triphenyl phosphine. [149]

PPh3 Triphenyl phosphine. [149]

KEX Potassium ethyl xanthate. [151,152]

KEX Potassium ethyl xanthate. [151,152]

2-Bromopropionic acid. [151,152]

2-Bromopropionic acid. [151,152]

GMA Glycidyl methacrylate. [153]

GMA Glycidyl methacrylate. [153]

XCA Xanthate carboxylic acid. [154]

XCA Xanthate carboxylic acid. [154]

[163]

[163]

[163]

[163]

[163]

[163]

[163]

EOX Ethylene oxide. [163]

EOX Ethylene oxide. [163]

EOX Ethylene oxide. [163]

EOX Ethylene oxide. [163]

EOX Ethylene oxide. [163]

EOX Ethylene oxide. [163]

EOX Ethylene oxide. [163]

PEO Poly(ethylene oxide). [161]

PEO Poly(ethylene oxide). [161]

PEO Poly(ethylene oxide). [161]

PEO Poly(ethylene oxide). [161]

PEO Poly(ethylene oxide). [161]

PEO Poly(ethylene oxide). [161]

1-tert-butyl-4,4,4-tris (dimethylamino)-2,2 bis[tris(dimethylamino)- phosphoranylidenamino]-2l5,4l5-catenadi (phosphazene)

**7. Conclusions** 

solution in hexane.

**7. Conclusions** 

**7. Conclusions** 

**7. Conclusions** 

**7. Conclusions** 

**7. Conclusions** 

**7. Conclusions** 

solution in hexane.

solution in hexane.

solution in hexane.

solution in hexane.

solution in hexane.

solution in hexane.

1-tert-butyl-4,4,4-tris (dimethylamino)-2,2 bis[tris(dimethylamino)- phosphoranylidenamino]-2l5,4l5-catenadi (phosphazene)

1-tert-butyl-4,4,4-tris (dimethylamino)-2,2 bis[tris(dimethylamino)- phosphoranylidenamino]-2l5,4l5-catenadi (phosphazene)

1-tert-butyl-4,4,4-tris (dimethylamino)-2,2 bis[tris(dimethylamino)- phosphoranylidenamino]-2l5,4l5-catenadi (phosphazene)

1-tert-butyl-4,4,4-tris (dimethylamino)-2,2 bis[tris(dimethylamino)- phosphoranylidenamino]-2l5,4l5-catenadi (phosphazene)

1-tert-butyl-4,4,4-tris (dimethylamino)-2,2 bis[tris(dimethylamino)- phosphoranylidenamino]-2l5,4l5-catenadi (phosphazene)

1-tert-butyl-4,4,4-tris (dimethylamino)-2,2 bis[tris(dimethylamino)- phosphoranylidenamino]-2l5,4l5-catenadi (phosphazene)

P4-t-Bu

P4-t-Bu

P4-t-Bu

P4-t-Bu

P4-t-Bu

P4-t-Bu

P4-t-Bu

**7. Conclusions** 

**7. Conclusions** 

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AMBN 2,2′-azobis (2-methylbutyronitrile). [154]

EOX 2-ethyl-2-oxazoline. [155]

PEOX Poly(2-ethyl-2-oxazoline). [155]

MOX 2-methyl-2-oxazoline. [156]

PMOX Poly(2-methyl-2-oxazoline). [156]

B-BL β-Butyrolactone. [160]

PHB Poly(3-hydroxybutyrate). [160]

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AMBN 2,2′-azobis (2-methylbutyronitrile). [154]

EOX 2-ethyl-2-oxazoline. [155]

PEOX Poly(2-ethyl-2-oxazoline). [155]

MOX 2-methyl-2-oxazoline. [156]

PMOX Poly(2-methyl-2-oxazoline). [156]

B-BL β-Butyrolactone. [160]

PHB Poly(3-hydroxybutyrate). [160]


**Table 19.** *Cont.*

#### **4. Characterization Techniques Used for Polymer Grafted Materials**

The characterization of polymer grafted materials requires the use of a variety of methods due to the many possible combinations of backbones and polymer grafts [59]. The characterization methods can be classified as direct or indirect.

Direct methods are those used to identify changes in the chemical structure of grafted materials, such as the bonds between backbone and grafts. These methods include proton and carbon magnetic nuclear resonance, <sup>1</sup>H-NMR, and <sup>13</sup>C-NMR, respectively.

Indirect methods are based on differences in properties between the starting and grafted materials, relating these changes to the modified structures. Microscopy and thermal analysis are examples of indirect methods. A summary of the main characterization methods used for grafted materials is presented in Table 6.

The relevant information contained in selected articles is also gathered in this review to show how the characterization techniques were used to provide evidence of polymer grafting onto the corresponding backbones. Tables 7–12 summarize the use of thermal, spectroscopic, imaging and microscopy, rheological, chromatographical, and mechanical characterization techniques, respectively, in the analysis of polymer grafted materials. Finally, a summary of biological, functional, and composition characterization techniques used for grafted materials is provided in Table 13.

#### **5. Modeling of Polymer Grafting**

#### *5.1. Literature review on Modeling of Polymer Grafting*

An overview of the literature on the modeling of polymer grafting is summarized in Table 14. The backbones considered, the functionalization methods, the polymer chains grafted, and summary comments on the modeling approaches used to carry out the simulations are included in the table.

#### *5.2. Modeling of Polymer Branching and Crosslinking*

As observed in Table 14, most reports on the modeling of polymer grafting are related to cases where grafting involves free-radical growth of the grafts, and the generation of active sites proceeds through chain transfer to polymer reactions. In that sense, the growth of polymer grafts resembles the formation and growth of branches in polymer branching. The difference would be that the branches and primary polymer chains contain the same monomers, whereas grafts and backbones contain different monomers in polymer grafting. There are several papers focused on the modeling of polymer branching [262–268]. In some cases, as in the grafting of monochlorotriazinyl-β-cyclodextrin onto cellulose, the activation mechanism is not specified, and the modeling approach is fully empirical (neural network modeling) [237–239].

.

In general terms, the polymerization scheme of FRP including chain transfer to polymer (CTP) is given by the reactions shown in Table 15. The specific mathematical expressions containing CTP terms are given by Equations (1)–(7). I, R, and M in Table 15 are initiator, primary free radical, and monomer molecules, respectively; P<sup>n</sup> and D<sup>m</sup> denote live and dead polymer molecules, respectively, of sizes n and m. k<sup>i</sup> , kp, ktd, and ktrp (also denoted as kfp in Equations (8) and (9)) denote initiation, propagation, termination by disproportionation, and chain transfer to polymer kinetic rate constants, respectively.

Polymer branching can be modeled using a bivariate distribution of chain length and number of branches resulting from polymerizations involving branched polymers [269]. Pn, b in Table 15 accounts for a bivariate distribution of live polymer of length n and number of branches b. The moment equations shown below consider only the kinetic steps of propagation and chain transfer to polymer, for illustrative purposes. For a batch reactor, the application of the mass action law considering only these two kinetic steps results in Equation (1) [269]. It should be noticed that in the transfer to polymer reaction there are as many possible sites of reaction as monomeric units in the dead polymer chain participating in the reaction.

$$\frac{dP\_{n,b}}{dt} = \dots - k\_p(P\_{n,b}M + P\_{n-1,b}M) \ - \mathbf{k\_{tp}}P\_{n,b} \left(\sum\_{m=1}^{\infty} \sum\_{\varepsilon=0}^{\infty} m D\_{\mathfrak{m},\varepsilon} \right) \\ + \mathbf{k\_{tp}}n D\_{n,b-1} \sum\_{h=1}^{\infty} \sum\_{\varepsilon=0}^{\infty} P\_{h,\varepsilon} + \dots \tag{1}$$
 
$$n = 1, \dots, \infty; b = 0, \dots, \infty$$

The bivariate moments for active and inactive polymer are defined respectively as shown in Equations (2) and (3). Number and weight-averaged molecular weights, and the average number of branches, are given by Equations (4)–(6) [269].

$$\mu\_{G,H} = \sum\_{n=1}^{\infty} \sum\_{b=0}^{\infty} n^G b^H P\_{n,b} \tag{2}$$

$$
\lambda\_{G,H} = \sum\_{n=1}^{\infty} \sum\_{b=0}^{\infty} n^G b^H D\_{n,b} \tag{3}
$$

$$M\_{\rm ll} = \frac{\mu\_{1,0} + \lambda\_{1,0}}{\mu\_{0,0} + \lambda\_{0,0}} W\_m \tag{4}$$

$$M\_w = \frac{\mu\_{2,0} + \lambda\_{2,0}}{\mu\_{1,0} + \lambda\_{1,0}} W\_m \tag{5}$$

$$B\_n = \frac{\mu\_{0,1} + \lambda\_{0,1}}{\mu\_{0,0} + \lambda\_{0,0}} \tag{6}$$

The moment equations for live polymer are given by Equation (7) [269].

$$\frac{d\mu\_{\rm G,H}}{dt} \dots - k\_{\rm p}M\mu\_{\rm G,H} + k\_{\rm p}M\sum\_{R=0}^{\rm G} \binom{\rm G}{R} \mu\_{\rm G-R,H} - k\_{\rm lrp}\mu\_{\rm G,H}\lambda\_{\rm L,0} + k\_{\rm lrp}\mu\_{\rm 0,0} \sum\_{K=0}^{H} \binom{H}{K} \lambda\_{\rm G+1,H} + \dots \tag{7}$$

Another approach with which to address the modeling of polymer branching in FRP is to use the concept of branching density, denoted as ρ, which is given by the ratio of the number of branching points to that of monomeric units, and it can be estimated using Equation (8), which when solved leads to Equation (9) [270]. kfp and k<sup>p</sup> in Equations (8) and (9) are chain transfer to polymer and propagation kinetic rate constants, respectively, and x is monomer conversion.

$$\frac{d(\mathbf{x}\rho)}{d\mathbf{x}} = \frac{k\_{fp}\mathbf{x}}{k\_p(1-\mathbf{x})} \tag{8}$$

$$\mathcal{B} = -\frac{k\_{fp}}{k\_p} \left[ 1 + \frac{\ln(1 - \chi)}{\chi} \right] \tag{9}$$

CTP and terminal double bond (TDB) polymerization produce tri-functional (long) branches, in addition to increasing the weight-averaged molecular weight and broadening the MWD. A reaction "similar" to TDB polymerization is the polymerization with internal

(pendant) double bonds (double bonds "internal" in dead polymer chains, appearing therein due to (co)polymerization of di-functional (divinyl) monomers (e.g., butadiene). Internal double bond (IDB) polymerization produces tetra-functional (long) branches and leads eventually to the formation of crosslinked polymer (gel). Both molecular weight averages increase due to IDB polymerization and the MWD broadens considerably [43]. Crosslinking can be considered as interconnected branching, and in that sense, its growth by CTP and its modeling in terms of a crosslink density, denoted as ρa, can also be taken as a useful basis for the modeling of polymer grating by CTP and propagation through the intermediate free radicals. Balance equations for polymer radicals of size r (R\* <sup>r</sup>) and ρ<sup>a</sup> for a case of copolymerization with crosslinking of vinyl/divinyl monomers, using the pseudo-kinetic rate constants method, are given by Equations (10) and (11), respectively, where P<sup>s</sup> is a dead polymer of size r; Q<sup>1</sup> is first-order moment for the dead polymer; and kcp and kcs are primary and secondary cyclization rate constants, respectively [271].

$$\begin{split} \frac{1}{\mathbf{V}} \frac{\mathbf{d}\left(\mathbf{V} \middle| \mathbf{R}\_{\mathbf{r}}^{\*}\right)}{\mathbf{d}\mathbf{t}} &= \mathbf{k}\_{\mathbf{P}} \left[\mathbf{M}\right] \left[\mathbf{R}\_{\mathbf{r}-1}^{\*}\right] + \mathbf{k}\_{\mathbf{f}} \mathbf{r} \left[\mathbf{P}\_{\mathbf{r}}\right] \left[\mathbf{R}^{\*}\right] + \mathbf{k}\_{\mathbf{p}}^{\*} \sum\_{s=1}^{\mathbf{r}-1} \mathbf{s} \left[\mathbf{R}\_{\mathbf{r}-s}^{\*}\right] \left[\mathbf{P}\_{\mathbf{s}}\right] \\ &- \left(\mathbf{k}\_{\mathbf{p}}^{\*}\right) \left[\mathbf{M}\right] \left[\mathbf{R}\_{\mathbf{r}}^{\*}\right] - \left(\mathbf{k}\_{\mathbf{td}} + \mathbf{k}\_{\mathbf{lc}}\right) \left[\mathbf{R}^{\*}\right] \left[\mathbf{R}\_{\mathbf{r}}^{\*}\right] - \left(\mathbf{k}\_{\mathbf{p}}^{\*} + \mathbf{k}\_{\mathbf{fp}}\right) \mathbf{Q}\_{1} \left[\mathbf{R}\_{\mathbf{r}}^{\*}\right] \end{split} \tag{10}$$

$$\frac{\mathbf{d}\left[\mathbf{x}\overline{\rho\_{\mathbf{a}}}\right]}{\mathbf{dt}} = \frac{\mathbf{k}\_{\mathbf{p}}^{\*}\left[\overline{\mathbf{F}\_{2}}(1-\mathbf{k}\_{\mathbf{cp}}) - \overline{\rho\_{\mathbf{a}}}(1+\mathbf{k}\_{\mathbf{cs}})\right] \times \mathbf{d}\mathbf{x}}{\mathbf{k}\_{\mathbf{p}}(1-\mathbf{x})} \frac{\mathbf{dx}}{\mathbf{dt}}\tag{11}$$

#### *5.3. Main Modeling Equations for Polymer Grafting*

Grafting efficiency (ε) and number average molecular weights for the different polymer populations (WIH, WSH, WII, WIS, and WSS) for the grafting of vinyl polymers onto pre-formed polymer with highly active chain transfer sites of (pendant mercaptan groups) are given by Equations (12)–(17) [39]. Subscripts IH and SH in the molecular weights shown in Equations (12)–(17) account for primary chains formed by chain transfer or by disproportionation termination (without distinguishing between terminally saturated and unsaturated chains) of polymer radicals starting with I and S fragments, respectively. Subscripts II, IS, and SS, on the other hand, account for primary chains produced by combination of the appropriate pair of polymer radicals starting with I and S fragments, respectively. r in Equations (12)–(18) is the ratio of propagation to termination kinetic rate constants, namely, r = kp/2k<sup>t</sup> .

$$\varepsilon = \frac{\mathcal{W}\_{SH} + \mathcal{W}\_{SS} + \mathcal{W}\_{IS}}{\mathcal{W}\_{SH} + \mathcal{W}\_{SS} + \mathcal{W}\_{IS} + \mathcal{W}\_{IH} + \mathcal{W}\_{II}} \tag{12}$$

$$\mathcal{W}\_{IH} = m[M]\_0 \int\_0^\infty \left\{ \frac{y\_0}{y\_0 + (1 - \infty)^{\mathbb{C}\_S}} - \frac{(1 - r)y\_0^2}{\left[ y\_0 + (1 - \infty)^{\mathbb{C}\_S} \right]^2} \right\} d\,\mathrm{or}\tag{13}$$

$$\mathcal{W}\_{SH} = m[M]\_0 \int\_0^\infty \left\{ \frac{(1-\alpha)^{\mathbb{C}\_S}}{y\_0 + (1-\alpha)^{\mathbb{C}\_S}} - \frac{(1-r)y\_0(1-\alpha)^{\mathbb{C}\_S}}{\left[y\_0 + (1-\alpha)^{\mathbb{C}\_S}\right]^2} \right\} d\alpha \tag{14}$$

$$\mathcal{W}\_{II} = m[\mathcal{M}]\_0 \int\_0^\infty \left\{ \frac{(1-r)y\_0^3}{\left[y\_0 + (1-\infty)^{\mathcal{C}\_S}\right]^3} \right\} \mathbf{d} \propto \tag{15}$$

$$\mathcal{W}\_{IS} = 2m[M]\_0 \int\_0^\infty \left\{ \frac{(1-r)y\_0^2(1-\infty)^{\mathcal{L}\_S}}{\left[y\_0 + (1-\infty)^{\mathcal{L}\_S}\right]^3} \right\} \mathbf{d} \,\,\mathbf{x} \tag{16}$$

$$\mathcal{W}\_{\rm SS} = m[\mathcal{M}]\_0 \int\_0^\infty \left\{ \frac{(1-r)y\_0(1-\infty)^{2\mathcal{C}\_S}}{\left[y\_0 + (1-\infty)^{\mathcal{C}\_S}\right]^3} \right\} \mathbf{d} \,\,\approx\tag{17}$$

An example of calculation of the mole fraction chain length distribution (number distribution) (nx) for the case of polymer grafting of vinyl polymers onto solid polymeric substrates, considering no chain transfer and incomplete conversion, is shown in Equation (18) [40].

$$m\_{\mathbf{x},1} = \frac{[R\_0]}{r[M]\_0 \left\{ 1 - \left(\frac{[M]}{[M]\_0}\right)^{1/r} \right\}} \left\{ 1 + \frac{[R\_0](1-r)\mathbf{x}}{r[M]\_0} \right\}^{\frac{r-2}{1-r}} \tag{18}$$

When addressing the modeling of polymer grafting of vinyl polymer onto polyolefins in extruders by CTP, Hamielec et al. [231] proposed a polymerization scheme and the corresponding kinetic equations where the prepolymer molecule bears abstractable hydrogens on its backbone and a second compound, denoted as additive (A), is bound to the prepolymer backbone via reaction with a free radical. The backbone radical then transfers its radical center to the active molecules. The radical is finally terminated with other radicals. Proper kinetic equations were written down for the participating species, and a degree of grafting, g, which is the average of number of grafted molecules per monomer unit on the prepolymer backbone, was defined as shown in Equation (19), where Q<sup>1</sup> is the concentration of monomer units on prepolymer backbones which remains constant during branching, Ka,3 is the kinetic coefficient for the grafting (additive addition) reaction, and R<sup>03</sup> designates a primary radical with radical center on backbone R0. Further mathematical treatment by the authors leads to Equation (20) for calculation of the full chain length distribution of the polymer population, w(r,s), where w0(r) is the initial chain length distribution of the prepolymer [231].

$$\frac{d\mathcal{g}}{dt} = \frac{K\_{a,3}R\_{0,3}A}{Q\_1} \tag{19}$$

$$w(r,s) = \left(1 + \frac{s}{r}\right) \frac{w\_0(r)}{(1+g)s!} (gr)^s e^{-gr} \tag{20}$$

As stated above in Table 14, Gianoglio Pantano et al. [245] developed a very detailed model for grafting of PSty onto PE. Among the concentrations of species calculated by the model, the concentration of poly(ethylene-g-styrene) is calculated using Equation (21), and the concentration of grafted PS, denoted as Gr, is obtained from Equation (22). **G**(t) is a matrix array of "infinite" size whose elements contain the molar concentrations of the individual species with degree of polymerization indicated by its subscripts. **VG** is a vector that contains the corresponding reaction rate terms, I1,0 is a bivariate moment of order 1 for PS and order 0 for PE, which represents the mass of PS grafted onto PE, and MPS <sup>1</sup> is the molar mass of PS.

$$\frac{d\mathbf{G}(t)}{dt} = \mathbf{V}\mathbf{G};\ \mathbf{G}(\mathbf{0}) = \mathbf{0} \tag{21}$$

$$Gr = 100 \frac{I\_{1,0}}{M\_1^{PS}(t=0)} \tag{22}$$

Very detailed simulation studies for the grafting of vinyl polymers onto PE using kMC were presented by Hernández-Ortiz et al. [41,259–261]. Some of the key reactions considered in this study are shown in Figure 7 and the modeling strategy is summarized in Figure 8 [259].

**Figure 7.** Some of the key reactions present in the grafting of polyolefins with vinyl monomer M. Reprinted with permission from Hernández-Ortiz et al., AIChE J., 63(11), 4944–4961 [259]. Copyright 2017 John Wiley and Sons, New York. **Figure 7.** Some of the key reactions present in the grafting of polyolefins with vinyl monomer M. Reprinted with permission from Hernández-Ortiz et al., AIChE J., 63(11), 4944–4961 [259]. Copyright 2017 John Wiley and Sons, New York.

**Figure 8.** Simulation approach using kMC for the grafting of polyolefins with vinyl monomer M. Reprinted with permission from Hernández-Ortiz et al., AIChE J., 63(11), 4944–4961 [259]. Copyright 2017 John Wiley and Sons, New York. **Figure 8.** Simulation approach using kMC for the grafting of polyolefins with vinyl monomer M. Reprinted with permission from Hernández-Ortiz et al., AIChE J., 63(11), 4944–4961 [259]. Copyright 2017 John Wiley and Sons, New York.

#### **6. Nomenclature, Symbols, Abbreviations, and Chemical Structures**  As mentioned earlier, symbols and abbreviations used in this contribution are de-**6. Nomenclature, Symbols, Abbreviations, and Chemical Structures**

fined and summarized in Tables 16–19. As mentioned earlier, symbols and abbreviations used in this contribution are defined and summarized in Tables 16–19.

#### **Table 16.** Symbols of application fields. **7. Conclusions**

**Symbol of Corresponding Application Meaning**  Biocomposites and biomaterials. Polymer grafting is a useful route for the synthesis of materials with interesting mechanical, thermal, dilute solution, and melt properties, and the ability to be compatible with otherwise incompatible mixtures. Systematic studies on polymer chemistry and characterization, and even modeling studies of polymer grafting started in about the 1950s. The interest in the grafting of natural biopolymers has escalated in the last 20 or so years due to environmental and sustainability issues.

Most of the studies on modeling of polymer grafting have focused on insertion of active sites on the backbone by CTP and growth of grafts by FRP or variants of FRP, such as RDRP. The monomers of major use for polymer grafting purposes are acrylic monomers (MMA, NIPAAM, AM, AA, BA), styrene (STY) and vinyl ethers [140,184]. When fine control of grafted structures is not required, polymer grafting by FRP may be enough. However, when precise control of polymer grafts (size and separation) is required, RDRP techniques, such as NMP, ATRP, and RAFT, are more adequate. RDRP polymer grafting techniques usually proceed by the "grafting-from" route [140,180,184]. One disadvantage

of RDRP techniques is that they require longer reaction times. For instance, polymer grafting by RAFT polymerization lasts from 8 to 48 h, plus the time required to prepare the related microcontrollers, which in many cases includes an esterification step through Steglich or anhydride procedures. Polymer grafting by ATRP takes from 24 h to several days.

Polymer grafting by ROP procedures using L-lactide (L-LA) and ε-caprolactone (CL) for the synthesis of poly(l-lactic acid) and poly(ε-caprolactone) polymer grafts is gaining importance [181,182,189]. Other monomers used are 2-ethyl-2-oxazoline, to produce PEOX, and ethylene glycol, to produce PEG. These reactions are commonly conducted at temperatures higher than 80 ◦C, which complicates solvent selection, when using metal catalysts such as Sn (Oct)2. Solvents should dissolve monomer and polymer, perform adequately at the selected temperatures, and show "green" characteristics. DMF, DMSO, p-dioxane, and toluene are some of the solvents most commonly used for polymer grafting by ROP. However, the recent advent of metal-free and organocatalyzed ROP has facilitated the polymerization at room temperature. For example, poly(lactide) materials can be made by ROP of L-LA at ambient conditions in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) [272].

Polymer grafting is also important in the synthesis of "dendrigraft copolymers." A large variety of heterogeneous dendrigraft copolymer architectures with core-shell and core-shell-corona morphologies can be produced, at significantly lower costs than for conventional dendrimer syntheses [18].

As observed in Table 14, the modeling of polymer grafting has focused on CTP or site formation by irradiation with FRP chemistry, in conventional flasks, stirred-tank reactors, or extruders. Other chemical routes have been addressed using semi-empirical approaches only. Therefore, there is still much to do in and contribute to this area.

**Author Contributions:** E.V.-L. and A.P. conceived the original idea (with discussions with A.R.-A., J.P.-A., M.G.H.-L., and A.M.). E.V.-L., M.G.H.-L., and A.M. assured funding acquisition through a project where experimental and theoretical work on polymer grafting of biopolymers from lignocellulosic biomasses has been carried out and provided background and motivation for this contribution. M.Á.V.-H., G.S.C.-D., A.R.-A., and E.V.-L. carried out critical literature reviews on different topics of the review. M.Á.V.-H., A.R.-A., and E.V.-L. wrote the original draft of the paper; E.V.-L., A.M., A.P., and Y.M. read and corrected different versions of the manuscript and provided extra references and discussion points. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by: (a) Consejo Nacional de Ciencia y Tecnología (CONACYT, México), PhD scholarships granted to M.A.V.-H. and G.S.C.-D.; (b) DGAPA-UNAM, Projects PAPIIT IG100718, IV100119, TA100818, and TA102120, granted to E.V.-L.—the first two—and to A.R.-A.—the last two; and PASPA sabbatical support to E.V.-L. while at the University of Waterloo, in Ontario, Canada; (c) Facultad de Química, UNAM, research funds granted to E.V.-L. (PAIP 5000-9078) and A.R.- A. (PAIP 5000-9167); (d) NSERC funding to A.P.; and (e) the Department of Chemical Engineering, University of Waterloo, Canada, partial sabbatical support to E.V.-L. with research funds from A.P. No funding was received for APC.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing is not applicable to this article.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

#### **References**

<sup>1.</sup> Hadjichristidis, N.; Pitsikalis, M.; Iatrou, H.; Driva, P.; Chatzichris, M.; Sakellariou, G.; Lohse, D. Graft copolymers. In *Encyclopedia of Polymer Science and Technology*, 2nd ed.; Matyjaszewski, K., Ed.; John Wiley & Sons: Hoboken, NJ, USA, 2010; pp. 1–38, ISBN 978-047-144-026-0.

