*Review* **A Review on the Synthesis, Characterization, and Modeling of Polymer Grafting**

**Miguel Ángel Vega-Hernández <sup>1</sup> , Gema Susana Cano-Díaz <sup>1</sup> , Eduardo Vivaldo-Lima 1,2,\* , Alberto Rosas-Aburto <sup>1</sup> , Martín G. Hernández-Luna <sup>1</sup> , Alfredo Martinez <sup>3</sup> , Joaquín Palacios-Alquisira <sup>4</sup> , Yousef Mohammadi <sup>5</sup> and Alexander Penlidis 2,\***


**Abstract:** A critical review on the synthesis, characterization, and modeling of polymer grafting is presented. Although the motivation stemmed from grafting synthetic polymers onto lignocellulosic biopolymers, a comprehensive overview is also provided on the chemical grafting, characterization, and processing of grafted materials of different types, including synthetic backbones. Although polymer grafting has been studied for many decades—and so has the modeling of polymer branching and crosslinking for that matter, thereby reaching a good level of understanding in order to describe existing branching/crosslinking systems—polymer grafting has remained behind in modeling efforts. Areas of opportunity for further study are suggested within this review.

**Keywords:** polymer grafting; polymer synthesis; polymer characterization; mathematical modeling; polymer reaction engineering; reversible deactivation radical polymerization

#### **1. Introduction**

Graft copolymers consist of branches of polymer segments covalently bonded to primary polymer chains. Graft copolymers containing a single branch are known as *miktoarm* star copolymers. The backbone and branches can be homo- or copolymers with different chemical structures or compositions [1]. However, if the polymer molecule is a homopolymer, the reaction route to produce the branches is known as polymer branching; polymer grafting is usually considered as a chemical route to produce materials whose branches are chemically different from the backbone or primary polymer chain. The branches typically have the same chain size and are randomly distributed throughout the backbone's length as a consequence of the synthetic route used synthesize them. However, more efficient methods that allow the synthesis of graft copolymers with equidistant and same-length branches, with which the microstructure and composition can be controlled to a remarkable level, have been developed [1]. From a surface-chemistry perspective, this definition of polymer grafting is extended to composites in which the main chain constitutes a diverse array of materials, ranging from brick and fiberglass to paper and wood [2]. Materials with improved or simply different polymer properties from mechanical, thermal, melt flow or dilute solution perspectives can be synthesized by polymer

**Citation:** Vega-Hernández, M.Á.; Cano-Díaz, G.S.; Vivaldo-Lima, E.; Rosas-Aburto, A.; Hernández-Luna, M.G.; Martinez, A.; Palacios-Alquisira, J.; Mohammadi, Y.; Penlidis, A. A Review on the Synthesis, Characterization, and Modeling of Polymer Grafting. *Processes* **2021**, *9*, 375. https://doi.org/10.3390/pr9020375

Academic Editor: Selestina Gorgieva Received: 4 December 2020 Accepted: 26 January 2021 Published: 18 February 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

grafting [1,3–7]. The structure–properties relationship has been an important issue in the analysis of polymer grafting [1].

Some of the first reports on polymer grafting available in the open literature (e.g., the oldest records available through Web of Science) include the grafting of polystyrene (PSty) [8] and poly(methyl methacrylate) (PMMA) [9] onto "government rubber styrene" (GRS) [8], which is a synthetic copolymer of butadiene and styrene, or onto natural rubber [9]; grafting of PSty, poly(butyl methacrylate) (PBMA), poly(lauryl methacrylate) (PLMA), poly(methyl acrylate) (PMA), and poly(ethyl acrylate) (PEA) onto PMMA with pendant mercaptan groups [10]; grafting of polyacrylamide (PAM) onto polyacrylonitrile (PAN), or the other way around (PAN onto PAM) [11]; grafting of PMMA onto PAN [12]; grafting of PSty onto polyethylene (PE) [13]; and grafting of several polymers, such as PAN, PMMA, PSty, poly(acrylic acid) (PAA), and poly(vinylidene chloride) (PVDC), onto cellulose [14–16], to name a few. A more complete literature review on the chemistry of polymer grafting is summarized in Table 1.






poly(methyl acrylate); PMMA: poly(methyl methacrylate); PSty: polystyrene; PVDC: poly(vinylidene chloride); REX: reactive extrusion; SP: solution polymerization.

The renewed emphasis on the use of biobased monomers and biopolymers as a viable route to decrease (synthetic) polymer waste and disposal issues has invigorated the research efforts on the development of improved materials with important contents of biopolymers (frequently as backbones); grating is part of the synthetic procedure of such materials. These trends are in the scope of some recent review papers focused on polymer grafting, which include the grafting of polymers onto cellulose [27,28], chitin/chitosan [29,30], or polysaccharides in general [2,31].

The use of lignocellulosic waste as raw material for biorefining processes aimed at producing value-added chemicals or materials (e.g., bioethanol, cellulose, xylose, or hybrid materials, to name a few) has increased significantly since the start of the present century. Biorefineries from lignocellulosic waste require multistep processes, starting with pretreatment of the biomass. In this way, the constituent biopolymers are available for subsequent reactive processes [32–35]. The synthesis of value-added materials from lignocellulosic waste biomasses by using polymer grafting onto lignocellulose itself [36] or onto its individual components (cellulose [27], hemicellulose [37], or lignin [38]) represents an important route in the concept of biorefineries.

Although a few early studies focused on the mathematical descriptions of polymer grafting under specific circumstances—such as the calculation of grafting efficiency and molecular weight development of the grafted branches onto a pre-formed polymer containing pendant mercaptan groups capable of acting as effective chain transfer agents, based on a comprehensive kinetic model including chain transfer to polymer and bimolecular polymer radical termination [39], or the theoretical calculation of molecular weight distributions of vinyl polymers grafted onto solid polymeric substrates by irradiation, also based on a kinetic description of the growing of the grafted branches [40], and a few comprehensive recent models for other specific situations (e.g., the detailed description of free-radical polymerization (FRP)-induced branching in reactive extrusion of PE [41])—are indeed available, the fact is that the cases addressed by mathematical models are by far less common than the available experimental systems. The purpose of the present review is to first offer a rather detailed summary of what is known from a polymer chemistry angle about polymer grafting, with an emphasis on what backbones and grafts are used, how active sites on backbones are generated, and how polymer branches are grown or grafted, among other process details. The second objective is to review what polymer grafting situations have been modeled, which tools have been used, and what limitations persist. By doing that, we can show areas of opportunity. Do keep in mind that the system that motivated this study was the grafting of synthetic polymers onto lignocellulosic biopolymers.

#### **2. Chemistry of Polymer Grafting**

The main chemical routes for polymer grafting are the following: "grafting onto" (also referred as "grafting to"), "grafting from," and the macromonomer or macromer (or "grafting through") method [1,2,27,28]. There are general reviews focused on the synthesis of grafted copolymers [1,2]. The ranges of backbones and grafts, backbone activating methods, graft growing (polymerization) routes, characterization techniques, quantification methods of grafting and branching molar mass distributions, and applications are so vast that reviews on specific aspects or subtopics related to these issues have been written. For instance, there are reviews focused on the grafting of polymer branches onto natural polymers [42] and biofibers [43]; grafting onto cellulose [27] or cellulose nanocrystals [28]; grafting onto chitin/chitosan [29,30]; microwave-activated grafting [31,44]; laccase-mediated grafting onto biopolymers and synthetic polymers [2]; radiation-induced RAFT-mediated graft copolymerization [45]; and polymer grafting onto inorganic nanoparticles [46] to name a few.

Herein, brief descriptions of such chemical routes are provided. In Table 1 we provide an overview of the grafted copolymer materials synthesized in the 1950–1970 period, plus some additional more recent cases, considering backbone structure, functionalization or active site generation techniques or procedures, grafted arm structure, polymer grafting

technique, polymer grafting conditions, measured properties and characterization methods, and related references. The literature on polymer grafting onto cellulose, chitin/chitosan, lignocellulosic biopolymers, other polysaccharides and natural biopolymers, inorganic materials, and metallic surfaces is addressed in the subsequent sections of this review. "Grafting to" and "grafting from" are the most common polymer grafting chemical routes. Better defined graft segments are obtained by the "grafting to" technique since the polymerization is independent of the union between the backbone and grafts. In contrast, materials of higher grafting densities can be produced by the "grafting from" route due to

or active site generation techniques or procedures, grafted arm structure, polymer grafting technique, polymer grafting conditions, measured properties and characterization methods, and related references. The literature on polymer grafting onto cellulose, chitin/chitosan, lignocellulosic biopolymers, other polysaccharides and natural biopolymers, inorganic materials, and metallic surfaces is addressed in the subsequent sections of this

As stated earlier, polymer grafting can proceed by the "grafting to" technique, where

a polymer molecule with a reactive end group reacts with the functional groups present in the backbone; by "grafting from," where polymer chains are formed from initiating sites within the backbone; and by "grafting through," where a macromolecule with a reactive end group copolymerizes with a second monomer of low molecular weight. Simplified rep-

#### *2.1. Types of Polymer Grafting* the lack of steric hindrance restrictions [47].

*2.1. Types of Polymer Grafting* 

review.

As stated earlier, polymer grafting can proceed by the "grafting to" technique, where a polymer molecule with a reactive end group reacts with the functional groups present in the backbone; by "grafting from," where polymer chains are formed from initiating sites within the backbone; and by "grafting through," where a macromolecule with a reactive end group copolymerizes with a second monomer of low molecular weight. Simplified representations of these grafting techniques are shown in Figure 1. However, each polymer grafting route has its own advantages and disadvantages in terms of chemical nature, density, dispersity, and length of the grafts obtained, and the ease and efficiency of the chemical reactions involved. Interestingly, different polymer grafting routes can be combined to produce specific grafted materials [48].

*Processes* **2021**, *9*, x FOR PEER REVIEW 6 of 91

resentations of these grafting techniques are shown in Figure 1.

#### **Figure 1.** Polymer grafting chemical routes. **Figure 1.** Polymer grafting chemical routes.

*2.2. Main Backbones Used in Polymer Grafting*  A polymer backbone is a polymer molecule that supports polymeric side chains, called branches or grafts. Side chains can be inserted onto the backbone during the syn-"Grafting to" and "grafting from" are the most common polymer grafting chemical routes. Better defined graft segments are obtained by the "grafting to" technique since the polymerization is independent of the union between the backbone and grafts. In contrast, materials of higher grafting densities can be produced by the "grafting from" route due to the lack of steric hindrance restrictions [47].

thesis of the backbone (copolymerization situation) or as a post-production process of the backbone [49]. In the first case, polymers with homogeneous bulk properties are obtained. The second case is very attractive since it allows the modification of many polymeric ma-However, each polymer grafting route has its own advantages and disadvantages in terms of chemical nature, density, dispersity, and length of the grafts obtained, and the ease and efficiency of the chemical reactions involved. Interestingly, different polymer grafting routes can be combined to produce specific grafted materials [48].

#### terials, including natural and synthetic fibers, or inorganic and metal particles. Backbones processed by polymer modification do not usually show significant changes in bulk prop-*2.2. Main Backbones Used in Polymer Grafting*

erties. Surface modification is often carried out following a "grafting from" technique; that is why this method is also known as surface initiated polymerization (SIP) [50]. The backbones used for polymer grafting can be synthetic polymers, biopolymers, or inorganic and metal surfaces. A polymer backbone is a polymer molecule that supports polymeric side chains, called branches or grafts. Side chains can be inserted onto the backbone during the synthesis of the backbone (copolymerization situation) or as a post-production process of the backbone [49]. In the first case, polymers with homogeneous bulk properties are obtained. The second case is very attractive since it allows the modification of many polymeric materials, including natural and synthetic fibers, or inorganic and metal particles. Backbones processed by polymer modification do not usually show significant changes in bulk properties. Surface modification is often carried out following a "grafting from" technique; that is why this method is also known as surface initiated polymerization (SIP) [50]. The backbones used for polymer grafting can be synthetic polymers, biopolymers, or inorganic and metal surfaces.

Synthetic polymers are human-made polymers and include a wide variety of materials, such as polyolefins, vinyl and fluorinated polymers, nylons, etc. The applications of synthetic graft copolymers include the synthesis of antifouling membranes [51], stimuliresponse materials [52], and biomedical applications [53].

Biopolymers are produced by the cells of living organisms. Polysaccharides have become important lately because of their characteristics of availability, biocompatibility, low cost, and non-toxicity, making them candidates for substitution of petroleum-based materials [47]. Polysaccharide-based graft copolymers are used as drug delivery carrier, food packaging and wastewater treatment [54]. Some of the most studied polysaccharides are cellulose [27,28], lignin [55], chitin/chitosan [29,56–58], starch [59], and various gums [42].

Surface functionalization of inorganic and metallic particles that allow the incorporation of polymer shells by polymer grafting has also become important, since polymer coatings alter the interfacial properties of the modified particles. Zhou et al. reviewed different applications for inorganic and metallic particles grafted with biopolymers [50]. One important inorganic surface modified by polymer grafting is silica [60].

#### *2.3. Backbone Functionalization Methods*

Several chemical modification procedures have been developed due to the wide variety of backbones of interest. Chemical modification reactions depend on the functional groups (or absence thereof) along the backbone. Two main chemical routes used to attach, grow, or graft polymer molecules onto lignin have been proposed [55]: (a) creation of new chemically active sites, and (b) functionalization of hydroxyl groups.

The introduction of functional groups into a polymer backbone increases its reactivity, making it accessible for forward polymerization or coupling reactions. Functionalization reactions are therefore required to generate the end functional pre-formed polymer or the reactive end of the macromolecule species involved in the "grafting to" and "grafting through" polymer grafting techniques, respectively. Functionalization is also required in the formation of the macromolecular species, such as macro-initiators and macro-controllers, involved in the "grafting from" polymer grafting technique [27,61]. The most important functionalization reactions involved in polymer grafting include sulfonation, esterification, etherification, amination, phosphorylation, and thiocarbonation, among others.

#### *2.4. Backbone Activation Methods*

Another way to generate grafting sites within the polymer backbone is to use polymer grafting activators, such as free-radical initiators. As shown in Figure 2, polymer grafting activators can be classified into physical, chemical, and biological. The main characteristics of these activators are highlighted in Sections 2.4.1–2.4.4.

**Figure 2.** Backbone activators used for polymer grafting. **Figure 2.** Backbone activators used for polymer grafting.

#### 2.4.1. Physical Activators 2.4.1. Physical Activators

opolymer [65].

High energy radiation, also referred to as ionizing radiation, includes γ-beam and electron-beam radiations. Radiation-promoted grafting may follow one of three possible routes: (a) pre-irradiation of the backbone in the presence of an inert gas to generate free radicals before placing the backbone in contact with monomers; (b) pre-irradiation of the backbone in an environment containing air or oxygen to produce hydroperoxides or diperoxides in its surface, followed by high temperature reaction with monomer; and (c) the High energy radiation, also referred to as ionizing radiation, includes γ-beam and electron-beam radiations. Radiation-promoted grafting may follow one of three possible routes: (a) pre-irradiation of the backbone in the presence of an inert gas to generate free radicals before placing the backbone in contact with monomers; (b) pre-irradiation of the backbone in an environment containing air or oxygen to produce hydroperoxides or diperoxides in its surface, followed by high temperature reaction with monomer; and (c) the mutual irradiation technique, where backbone and monomer are irradiated simultaneously to generate free radicals [62].

mutual irradiation technique, where backbone and monomer are irradiated simultaneously to generate free radicals [62]. Plasma is a partially ionized gas where free electrons, ions, and radicals are mixed. Different functional groups can be introduced, or free radicals can be generated on back-Plasma is a partially ionized gas where free electrons, ions, and radicals are mixed. Different functional groups can be introduced, or free radicals can be generated on backbones by this process, depending on the gas used. Polymer grafting reactions carried out in plasma are sometimes classified as high energy radiation reactions [63].

bones by this process, depending on the gas used. Polymer grafting reactions carried out in plasma are sometimes classified as high energy radiation reactions [63]. The absorption of UV light on the surface of the material generates free radicals that serve as nucleation sites. The surface is then placed in contact with monomer for subsequent polymerization [64].

The absorption of UV light on the surface of the material generates free radicals that serve as nucleation sites. The surface is then placed in contact with monomer for subsequent polymerization [64]. Microwave irradiation consists of direct interaction of electromagnetic irradiation with polar molecules and ionic particles, promoting very fast non-contact internal heating, Microwave irradiation consists of direct interaction of electromagnetic irradiation with polar molecules and ionic particles, promoting very fast non-contact internal heating, which enhances reaction rates and leads to higher yields. Singh et al. carried out a successful polymerization of acrylamide on guar gum under microwave irradiation [65]. They proposed a mechanism in which free radicals are produced within the polysaccharide backbone by the effect of microwave irradiation on the hydroxyl groups of the biopolymer [65].

which enhances reaction rates and leads to higher yields. Singh et al. carried out a successful polymerization of acrylamide on guar gum under microwave irradiation [65].

ride backbone by the effect of microwave irradiation on the hydroxyl groups of the bi-

#### 2.4.2. Chemical Activators

As shown in Figure 1, chemical activators include free radical and backbone oxidant initiators. Free radical initiators are compounds that present either direct or indirect homolytic fission. The first case involves the initiator itself and the second one requires participation of another molecule from the environment [66].

Oxidant initiators react directly with functional groups from the backbone, generating activation sites. Polymer grafting of polysaccharides using oxidant initiators has been reported in the literature [66].

#### 2.4.3. Biological Activators

Enzymes catalyze polymer modification reactions through functional groups located at chain ends, along the main chain, or at side branches, promoting highly specific nondestructive transformations on backbones, under mild reaction conditions. Successful grafting of lignin by oxidation of its phenolic structures using laccases has been reported recently [2].

#### 2.4.4. Combined Activators

Combinations of physical and chemical activators for polymer grafting have been successfully carried out. For instance, microwave assisted polymerization (MAP) has been combined with the use of chemical activators for the production of hydrogels synthesized by crosslinking graft copolymerization, taking advantage of the short reaction times required to obtain high yields [67,68]. Enzymes are also used in combination with radical initiators for more effective grafting copolymerization processes [69,70].

#### *2.5. Polymer Grafting by Free-Radical Polymerization*

As stated earlier, the "grafting through" and "grafting from" techniques require a polymerization reaction to bond the polymer grafts to the backbone. Different polymerization methods have been used for polymer grafting, but the most effective ones use free radical methods (e.g., FRP, RDRP, and REX), due to their versatility to work with different chemical groups, and their tolerance to impurities. A short overview on free-radical polymerization reactions is presented in Table 2. Polymer grafting by FRP, and other reactions, is affected by several factors, including the chemical nature of the components contained in the system—backbone, monomer, initiator, and solvent—and the interactions among them. Other aspects related to polymer grafting, including temperature and the use of additives, need to be considered [67]. The synthetic routes and activators used in graft polymerization provide a variety of interesting and versatile routes for this type of polymer modification.




**Table 2.** *Cont.*

#### **3. Backbones and Supports Used in Polymer Grafting**

As explained earlier, grafted materials consist of side chains or arms attached to primary polymers referred to as backbones. The purpose of polymer grafting is to combine chemical, mechanical, interfacial, electrical, or other polymer properties between the constituent materials. The diversity of backbones and the ways in which side chains are attached to them through polymer grafting will be briefly overviewed in this section.

#### *3.1. Cellulose, Lignin, and Lignocellulosic Biomasses as Backbones*

Lignocellulosic biopolymers are abundant in nature. They are made of cellulose, hemicellulose, and lignin. They also contain moisture, extractive organic compounds, and ashes from inorganic compounds in lesser amounts. Each of these components has distinct characteristics. The extractive organic compounds present in lignocellulosic biopolymers are oligomers and oligosaccharides of low molecular weight, sugars, fatty acids, resins, etc. [76].

Cellulose, hemicellulose, and lignin can be modified by polymer grafting leading to new promising materials with interesting properties. However, the extractables are not useful for this purpose since they are not part of a skeleton or stiff structure that may provide support or mechanical stability. Extractables also consume reactants required for the grafting process. They are usually removed prior to the polymer grafting process, although in some studies, they remain in the system during the formation of grafted arms [77].

Polymer grafting of xylan onto lignin has been studied since the early 1960s. Early reports on the topic reported the grafting of organic polymers, such as 4-methyl-2-oxy-3 oxopent-4-ene and methyl methacrylate polymers [78,79], xylan [80], ethylbenzene, and styrene [81–84], onto lignin or lignin derivatives. The topic of polymer grafting of synthetic polymers onto lignocellulosic biopolymers has gained renewed relevance in the last two decades due to environmental and sustainability issues [27,85–94].






28




Cellulose can be extracted from lignocellulose and used as such or modified for other applications. Table 3 provides an overview of grafting of synthetic polymers onto cellulose and natural fibers. (See the tables of Section 6 for explanation of abbreviations and symbols.) *Processes* **2021**, *9*, x FOR PEER REVIEW 17 of 91

> Lignin follows cellulose in abundance on earth, providing a primary natural source of aromatic compounds [125]. Several industrial applications have been attempted for lignin [55, 125–127] but not all of them have succeeded due to different reasons [125,128–130]. Lignin follows cellulose in abundance on earth, providing a primary natural source of aromatic compounds [125]. Several industrial applications have been attempted for lig-

> Marton [8] described fifty-four different constituents that can be found in lignin based on interpretation of experimental data from biochemical degradation, oxidation, and other ways of decomposition of different types of lignin materials. The combinations and proportions among these structures lead to different properties of lignin materials. Three decades later, Lewis and Sarkanen [130] organized these fifty-four structures into a map that they called phenylpropanoid pathway. As observed in Figure 3, lignins and lignans are monolignol derived compounds. Sharma and Kumar described lignin as a complex material consisting mostly of three single unit lignol precursors, coniferyl alcohol, p-coumaryl alcohol, and sinapyl alcohol, along with other atypical monolignol constitutive units in trace amounts [55]. nin [55,125–127] but not all of them have succeeded due to different reasons [125,128–130]. Marton [8] described fifty-four different constituents that can be found in lignin based on interpretation of experimental data from biochemical degradation, oxidation, and other ways of decomposition of different types of lignin materials. The combinations and proportions among these structures lead to different properties of lignin materials. Three decades later, Lewis and Sarkanen [130] organized these fifty-four structures into a map that they called phenylpropanoid pathway. As observed in Figure 3, lignins and lignans are monolignol derived compounds. Sharma and Kumar described lignin as a complex material consisting mostly of three single unit lignol precursors, coniferyl alcohol, p-coumaryl alcohol, and sinapyl alcohol, along with other atypical monolignol constitutive units in trace amounts [55].

**Figure 3.** Main steps of the phenylpropanoid pathway: lignins and lignans are monolignol derived. 1, phenylalanine ammonia-lyase; 2, tyrosine ammonia-lyase (mostly in grasses); 3, cinnamate-4-hydroxylase; 4, hydroxylases; 5, CoA ligases involving AMP and CoA ligation, respectively; 6, O-methyltransferases; 7, cinnamoyl-CoA:NADP oxidoreductases; 8, cinnamyl alcohol dehydrogenases; 9, chalcone synthase; 10, chalcone isomerase. (Note: conversions from 7-coumaric acid to sinapic acid and corresponding CoA esters are marked in boxes since dual pathways seem to take place; \*: may also involve 7-coumaryl and feruloyl tyramines, and small amounts of single unit lignols). Source: Adapted with permission from Lewis N. G. and Sarkanen S. (1998). Lignin and Lignan Biosynthesis, Washington, D.C.: Oxford University Press pp. 6–7 [130] Copyright © 2021 by American Chemical Society. The process used for lignin extraction and the final properties of the material depend **Figure 3.** Main steps of the phenylpropanoid pathway: lignins and lignans are monolignol derived. 1, phenylalanine ammonia-lyase; 2, tyrosine ammonia-lyase (mostly in grasses); 3, cinnamate-4-hydroxylase; 4, hydroxylases; 5, CoA ligases involving AMP and CoA ligation, respectively; 6, O-methyltransferases; 7, cinnamoyl-CoA:NADP oxidoreductases; 8, cinnamyl alcohol dehydrogenases; 9, chalcone synthase; 10, chalcone isomerase. (Note: conversions from 7-coumaric acid to sinapic acid and corresponding CoA esters are marked in boxes since dual pathways seem to take place; \*: may also involve 7-coumaryl and feruloyl tyramines, and small amounts of single unit lignols). Source: Adapted with permission from Lewis N. G. and Sarkanen S. (1998). Lignin and Lignan Biosynthesis, Washington, D.C.: Oxford University Press pp. 6–7 [130] Copyright © 2021 by American Chemical Society.

on the type of biomass employed [55]. Lignin is obtained from woods, which can be hard, soft, bushes, rinds, husks, corncobs, either products or residues. A pulp is obtained from these materials. The yield of lignin extraction depends on temperature, time, dispersion media, extraction method, and the amount of lignin present in the raw material. Lignin extraction methods can be biological or enzymatic, physical, or chemical. Integrated solu-The process used for lignin extraction and the final properties of the material depend on the type of biomass employed [55]. Lignin is obtained from woods, which can be hard, soft, bushes, rinds, husks, corncobs, either products or residues. A pulp is obtained from these materials. The yield of lignin extraction depends on temperature, time, dispersion

tions are employed at the end to remove impurities from lignin so it can be bleached [55].

istry.

media, extraction method, and the amount of lignin present in the raw material. Lignin extraction methods can be biological or enzymatic, physical, or chemical. Integrated solutions are employed at the end to remove impurities from lignin so it can be bleached [55]. The complex structure of lignin contains specific surface moieties that provide reactive sites where polymers and other species can be synthesized, bonded, or modified [55]. These moieties were recognized as hydroxyl, carboxyl, carbonyl, and methoxyl groups. The complex structure of lignin contains specific surface moieties that provide reactive sites where polymers and other species can be synthesized, bonded, or modified [55]. These moieties were recognized as hydroxyl, carboxyl, carbonyl, and methoxyl groups. There are two main routes for grafting of polymer chains onto lignin-based biopoly-

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There are two main routes for grafting of polymer chains onto lignin-based biopolymers [55]: (a) synthesis of new reactive sites within lignin's structure; and (b) modification or functionalization of lignin's hydroxyl groups. Route (a) allows lignin to become more reactive, both at the surface, and within the bulk. Polymer modification by route (a) improves both, the properties of lignin and those of the modified materials. mers [55]: (a) synthesis of new reactive sites within lignin's structure; and (b) modification or functionalization of lignin's hydroxyl groups. Route (a) allows lignin to become more reactive, both at the surface, and within the bulk. Polymer modification by route (a) improves both, the properties of lignin and those of the modified materials. In route (b), a good number of functional groups can be placed in the end groups of

In route (b), a good number of functional groups can be placed in the end groups of lignin (what is sometimes referred to as the surface of lignin). Katahira et al. [131] identified seven side chain structures in the end groups of lignin: p-coumarate, ferulate, hydroxycinnamyl alcohol, hydroxycinnamaldehyde, arylglycerol, dihydrocinnamyl alcohol, and guaiacylpropane-1,3-diol end-units, as shown in Figures 4 and 5 [131]. However, it has been proposed that the phenolic hydroxyl groups shown in Figure 4, and the aliphatic hydroxyl functional groups corresponding to C-α and C-γ positions of the side molecule fragment shown in Figure 5, are the most reactive [55]. Both routes allow one to produce grafted materials, mainly polymers, and most of them come from route (b) above [85,132,133]. Further reports on lignin treatments and grafting can be found elsewhere [55,91,125,128]. lignin (what is sometimes referred to as the surface of lignin). Katahira et al. [131] identified seven side chain structures in the end groups of lignin: p-coumarate, ferulate, hydroxycinnamyl alcohol, hydroxycinnamaldehyde, arylglycerol, dihydrocinnamyl alcohol, and guaiacylpropane-1,3-diol end-units, as shown in Figure 4 and Figure 5 [131]. However, it has been proposed that the phenolic hydroxyl groups shown in Figure 4, and the aliphatic hydroxyl functional groups corresponding to C-α and C-γ positions of the side molecule fragment shown in Figure 5, are the most reactive [55]. Both routes allow one to produce grafted materials, mainly polymers, and most of them come from route (b) above [85,132,133]. Further reports on lignin treatments and grafting can be found elsewhere [55,91,125,128].

**Figure 4.** Repeating units in lignin. From left to right: p-hydroxyphenyl, guaiacyl, metoxy guaiacyl, syringyl, metoxi syringyl, p-coumaryl alcohol, coniferyl alcohol, synapyl alcohol. Source: Adapted with permission from Katahira et al. (2018). Lignin Valorization. Emerging Approaches: Croydon UK pp. 3 [131]. Copyright © 2021 The Royal Society of Chem-**Figure 4.** Repeating units in lignin. From left to right: p-hydroxyphenyl, guaiacyl, metoxy guaiacyl, syringyl, metoxi syringyl, p-coumaryl alcohol, coniferyl alcohol, synapyl alcohol. Source: Adapted with permission from Katahira et al. (2018). Lignin Valorization. Emerging Approaches: Croydon UK pp. 3 [131]. Copyright © 2021 The Royal Society of Chemistry.

**Figure 5.** Side chain structure in end-groups in lignin. From left to right: p-coumarate, ferulate, hydroxycinnamyl alcohol, hydroxycinnamaldehyde, dihydroycinnamyl alcohol, arylpropane-1,3-diol, arylglycerol end units. Source: Adapted with permission from Katahira et al. (2018). Lignin Valorization. Emerging Approaches: Croydon UK pp. 5 [131] Copyright © 2021 The Royal Society of Chemistry. **Figure 5.** Side chain structure in end-groups in lignin. From left to right: p-coumarate, ferulate, hydroxycinnamyl alcohol, hydroxycinnamaldehyde, dihydroycinnamyl alcohol, arylpropane-1,3-diol, arylglycerol end units. Source: Adapted with permission from Katahira et al. (2018). Lignin Valorization. Emerging Approaches: Croydon UK pp. 5 [131] Copyright © 2021 The Royal Society of Chemistry.

The overview on grafting of synthetic polymers onto cellulose and other lignocellulosic biopolymers presented in Table 3 is further expanded in Table 4 to include other examples of lignocellulosic biomasses, and other natural biopolymers, such as polysaccharides, chitin, and chitosan. Examples of recent research reports (2020–2021) on synthesis of grafted polymers are provided in Table 5. Tables 6–13 contain extensive information related to characterization of polymer grafting. Table 14 summarizes the literature on modeling of polymer grafting. Table 15 shows the polymerization scheme of FRP including CTP and crosslinking. Finally, Tables 16–19 provide information on the many symbols and abbreviations used throughout the review. The overview on grafting of synthetic polymers onto cellulose and other lignocellulosic biopolymers presented in Table 3 is further expanded in Table 4 to include other examples of lignocellulosic biomasses, and other natural biopolymers, such as polysaccharides, chitin, and chitosan. Examples of recent research reports (2020–2021) on synthesis of grafted polymers are provided in Table 5. Tables 6–13 contain extensive information related to characterization of polymer grafting. Table 14 summarizes the literature on modeling of polymer grafting. Table 15 shows the polymerization scheme of FRP including CTP and crosslinking. Finally, Tables 16–19 provide information on the many symbols and abbreviations used throughout the review.




*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

**FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA,

Monomers and polymers grafted by:

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

analyzed by 1H NMR and GPC, using adequate solvents.

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), fol-

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

[140]

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

Grafting from Grafting through

Several techniques described in the review. Monomers copolymerized with natural ex-

and AA.

and AA.

which polymerized AM

which polymerized AM

Several procedures described.

from

lecular hydrogels, self-healing materials.

from

lyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

[140,148]

lecular hydrogels, self-healing materials.

which polymerized AM

analyzed by 1H NMR and GPC, using adequate solvents.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm

which polymerized AM

and AA.

which polymerized AM

and AA.


PMMA

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

tracts.

tion, washing and drying. Grafting was measured using 1H NMR.

from

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

analyzed by 1H NMR and GPC, using adequate solvents.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

and AA.

which polymerized AM

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

which polymerized AM

and AA.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

analyzed by 1H NMR and GPC, using adequate solvents.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

and AA.

which polymerized AM

Several techniques described in the review. Monomers copolymerized with natural ex-

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

which polymerized AM

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol. **ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

which polymerized AM

Several techniques described in the review. Monomers copolymerized with natural ex-

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

and AA.

tracts.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

tion, washing and drying. Grafting was measured using 1H NMR.

Several techniques described in the review. Monomers copolymerized with natural ex-

and AA.

ATRP NIPAAM PNIPAAM Grafting

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Several procedures described.

from

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

Grafting from Grafting through

from

[140]

from

bide, butanediol.

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

from

Grafting from Grafting through

Grafting from

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

from

Grafting from Grafting through

[140]

from

50 °C; Thermoresponsive material. [140,141]

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

tracts.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

ATRP DAEAPDAEA Grafting

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

analyzed by 1H NMR and GPC, using adequate solvents.

Several techniques described in the review. Monomers copolymerized with natural ex-

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Hydrophobic polymer composites. [140,142]

ATRP PEG-A; NIPAAM Grafting

ATRP DAEAPDAEA Grafting

Several procedures described.

ATRP NIPAAM PNIPAAM Grafting

Several procedures described.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

tion, washing and drying. Grafting was measured using 1H NMR.

tracts.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

which polymerized AM

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

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

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Several techniques described in the review. Monomers copolymerized with natural ex-

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

BMA PBMA

ATRP NIPAAM PNIPAAM Grafting

ATRP PEG-A; NIPAAM Grafting

ATRP MMA PMMA

analyzed by 1H NMR and GPC, using adequate solvents.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm

Thermoplastic elastomers. [140,144]

tracts.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA.

50 °C; Thermoresponsive material. [140,141]

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

50 °C; Thermoresponsive material. [140,141]

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), fol-

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

ATRP PEG-A; NIPAAM Grafting

SI-ATRP NIPAAM PNIPAAM Grafting

ATRP DAEAPDAEA Grafting

SI-ATRP NIPAAM PNIPAAM Grafting

from

tion, washing and drying. Grafting was measured using 1H NMR.

analyzed by 1H NMR and GPC, using adequate solvents.

from

Monomers and polymers grafted by:

[140]

Grafting from Grafting through

bide, butanediol.

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

analyzed by 1H NMR and GPC, using adequate solvents.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

tion, washing and drying. Grafting was measured using 1H NMR.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

analyzed by 1H NMR and GPC, using adequate solvents.

50 °C; Thermoresponsive material. [140,141]

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

analyzed by 1H NMR and GPC, using adequate solvents.

bide, butanediol.

Hydrophobic polymer composites. [140,142]

[140]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

50 °C; Thermoresponsive material. [140,141]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

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

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

analyzed by 1H NMR and GPC, using adequate solvents.

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

Hydrophobic polymer composites. [140,142]

[140]

Thermoplastic elastomers. [140,144]

50 °C; Thermoresponsive material. [140,141]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Softwood Kraft lignin; Catalyst: CuCl/HMTETA; Solvent: water; Room

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

temperature; Ionic responsive nanofibrous material. [140,145]

[140]

Hydrophobic polymer composites. [140,142]

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Thermoplastic elastomers. [140,144]

50 °C; Thermoresponsive material. [140,141]

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Kraft lignin (alkali); Lignin + STY lignin-g-PS; Catalyst:

bide, butanediol.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), fol-

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

Backbone: Softwood Kraft lignin; Catalyst: CuCl/HMTETA; Solvent: water; Room

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

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

[140]

[140]

Grafting from Grafting through

Several procedures described.

bide, butanediol.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

analyzed by 1H NMR and GPC, using adequate solvents.

which polymerized AM

and AA.

Several techniques described in the review. Monomers copolymerized with natural ex-

which polymerized AM

and AA.

which polymerized AM

Several procedures described.

ATRP NIPAAM PNIPAAM Grafting

Several techniques described in the review. Monomers copolymerized with natural ex-

and AA.

ATRP DAEAPDAEA Grafting

Several procedures described.

ATRP PEG-A; NIPAAM Grafting

tracts.

Several techniques described in the review. Monomers copolymerized with natural ex-

and AA.

which polymerized AM

ATRP MMA PMMA

Several techniques described in the review. Monomers copolymerized with natural ex-

tracts.

which polymerized AM

and AA.

BMA PBMA

ATRP NIPAAM PNIPAAM Grafting

Several procedures described.

SI-ATRP NIPAAM PNIPAAM Grafting

ATRP DAEAPDAEA Grafting

ATRP PEG-A; NIPAAM Grafting

tracts.

Several techniques described in the review. Monomers copolymerized with natural ex-

ATRP NIPAAM PNIPAAM Grafting

from

from

ATRP PEGMA Grafting

lyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

from

[140,148]

from

lecular hydrogels, self-healing materials.

lyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

lecular hydrogels, self-healing materials.

[140,148]

[140,148]

lyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

lecular hydrogels, self-healing materials.

lecular hydrogels, self-healing materials.

from

Grafting from Grafting through

from

from

Grafting from Grafting through

and AA.

bide, butanediol.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

Grafting from

from

Grafting from Grafting through

Grafting from Grafting through

tracts.

which polymerized AM

and AA.



Grafting from

Grafting through

Backbone: Kraft lignin (alkali); Lignin + STY lignin-g-PS; Catalyst:

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

Backbone: Softwood Kraft lignin; Catalyst: CuCl/HMTETA; Solvent: water; Room

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), fol-

Thermoplastic elastomers. [140,144]

SI-ATRP NIPAAM PNIPAAM Grafting

Thermoplastic elastomers. [140,144]

Hydrophobic polymer composites. [140,142]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

50 °C; Thermoresponsive material. [140,141]

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

tion, washing and drying. Grafting was measured using 1H NMR.

solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

**FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA,

from

ATRP NIPAAM PNIPAAM Grafting from

Grafting from

PMMA

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

analyzed by 1H NMR and GPC, using adequate solvents.

analyzed by 1H NMR and GPC, using adequate solvents.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

Grafting from Grafting through

analyzed by 1H NMR and GPC, using adequate solvents.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

and AA.

which polymerized AM

which polymerized AM

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

and AA.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

tion, washing and drying. Grafting was measured using 1H NMR.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

which polymerized AM

and AA.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

and AA.

which polymerized AM

analyzed by 1H NMR and GPC, using adequate solvents.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

Several techniques described in the review. Monomers copolymerized with natural ex-

analyzed by 1H NMR and GPC, using adequate solvents.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

tracts.

tion, washing and drying. Grafting was measured using 1H NMR.

Several techniques described in the review. Monomers copolymerized with natural ex-

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Several procedures described.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

analyzed by 1H NMR and GPC, using adequate solvents.

tion, washing and drying. Grafting was measured using 1H NMR.

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

ATRP NIPAAM PNIPAAM Grafting

Several procedures described.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

50 °C; Thermoresponsive material. [140,141]

tion, washing and drying. Grafting was measured using 1H NMR.

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

tracts.

from

[140]

ATRP NIPAAM PNIPAAM Grafting

[140]

Several procedures described.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

analyzed by 1H NMR and GPC, using adequate solvents.

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

50 °C; Thermoresponsive material. [140,141]

ATRP DAEAPDAEA Grafting

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Hydrophobic polymer composites. [140,142]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

tion, washing and drying. Grafting was measured using 1H NMR.

analyzed by 1H NMR and GPC, using adequate solvents.

ATRP NIPAAM PNIPAAM Grafting

from

ATRP NIPAAM PNIPAAM Grafting

ATRP DAEAPDAEA Grafting

bide, butanediol.

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

Hydrophobic polymer composites. [140,142]

ATRP PEG-A; NIPAAM Grafting

50 °C; Thermoresponsive material. [140,141]

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

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

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

50 °C; Thermoresponsive material. [140,141]

ATRP DAEAPDAEA Grafting

from

ATRP DAEAPDAEA Grafting

ATRP PEG-A; NIPAAM Grafting

[140]

from

Grafting from

from

BMA PBMA

ATRP PEG-A; NIPAAM Grafting

ATRP MMA PMMA

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Hydrophobic polymer composites. [140,142]

BMA PBMA

Hydrophobic polymer composites. [140,142]

ATRP PEG-A; NIPAAM Grafting

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

analyzed by 1H NMR and GPC, using adequate solvents.

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

ATRP MMA PMMA

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

Thermoplastic elastomers. [140,144]

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

tion, washing and drying. Grafting was measured using 1H NMR.

SI-ATRP NIPAAM PNIPAAM Grafting

[140]

Thermoplastic elastomers. [140,144]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

[140]

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

Several procedures described.

Grafting from Grafting through

Several techniques described in the review. Monomers copolymerized with natural ex-

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

[140]

Grafting from Grafting through

bide, butanediol.

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Grafting from Grafting through

bide, butanediol.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

50 °C; Thermoresponsive material. [140,141]

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

from

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

bide, butanediol.

Hydrophobic polymer composites. [140,142]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

from

from

from

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

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

50 °C; Thermoresponsive material. [140,141]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

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

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

50 °C; Thermoresponsive material. [140,141]

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Hydrophobic polymer composites. [140,142]

Thermoplastic elastomers. [140,144]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

Backbone: Softwood Kraft lignin; Catalyst: CuCl/HMTETA; Solvent: water; Room

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

temperature; Ionic responsive nanofibrous material. [140,145]

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Thermoplastic elastomers. [140,144]

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

Hydrophobic polymer composites. [140,142]

Grafting from

from

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

[140]

Thermoplastic elastomers. [140,144]

Backbone: Softwood Kraft lignin; Catalyst: CuCl/HMTETA; Solvent: water; Room

from

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

temperature; Ionic responsive nanofibrous material. [140,145]

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

from

Grafting from Backbone: Kraft lignin (alkali); Lignin + STY lignin-g-PS; Catalyst:

Backbone: Softwood Kraft lignin; Catalyst: CuCl/HMTETA; Solvent: water; Room

Backbone: Kraft lignin (alkali); Lignin + STY lignin-g-PS; Catalyst:

Backbone: Softwood Kraft lignin; Catalyst: CuCl/HMTETA; Solvent: water; Room

temperature; Ionic responsive nanofibrous material. [140,145]

PMMA

Thermoplastic elastomers. [140,144]

[140]

[140]

analyzed by 1H NMR and GPC, using adequate solvents.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

[140]

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

[140]

[140]

50 °C; Thermoresponsive material. [140,141]

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

Hydrophobic polymer composites. [140,142]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

bide, butanediol.

tracts.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

Several techniques described in the review. Monomers copolymerized with natural ex-

analyzed by 1H NMR and GPC, using adequate solvents.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

Grafting from Grafting through

Grafting from Grafting through

bide, butanediol.

which polymerized AM

and AA.

which polymerized AM

and AA.

which polymerized AM

and AA.

and AA.

which polymerized AM

Several techniques described in the review. Monomers copolymerized with natural ex-

which polymerized AM

Several techniques described in the review. Monomers copolymerized with natural ex-

and AA.

Several procedures described.

Several procedures described.

which polymerized AM

ATRP NIPAAM PNIPAAM Grafting

which polymerized AM

Several procedures described.

Several procedures described.

ATRP NIPAAM PNIPAAM Grafting

and AA.

tracts.

Several techniques described in the review. Monomers copolymerized with natural ex-

which polymerized AM

tracts.

ATRP DAEAPDAEA Grafting

ATRP DAEAPDAEA Grafting

and AA.

ATRP NIPAAM PNIPAAM Grafting

ATRP PEG-A; NIPAAM Grafting

Several procedures described.

ATRP NIPAAM PNIPAAM Grafting

ATRP PEG-A; NIPAAM Grafting

Several techniques described in the review. Monomers copolymerized with natural ex-

ATRP DAEAPDAEA Grafting

ATRP MMA PMMA

tracts.

which polymerized AM

ATRP DAEAPDAEA Grafting

ATRP MMA PMMA

and AA.

ATRP MMA PMMA

SI-ATRP NIPAAM PNIPAAM Grafting

ATRP MMA PMMA

Several techniques described in the review. Monomers copolymerized with natural ex-

ATRP MMA PMMA

ATRP MMA PMMA

ATRP MMA PMMA Grafting

SI-ATRP NIPAAM PNIPAAM Grafting

ATRP MMA PMMA

ATRP MMA PMMA Grafting

tracts.

ATRP PEGMA Grafting

ATRP NIPAAM PNIPAAM Grafting

ATRP MMA PMMA Grafting

ATRP PEGMA Grafting

ATRP PEGMA Grafting

ATRP PEG-A; NIPAAM Grafting

ATRP MMA PMMA Grafting

ATRP MMA PMMA

ATRP PEGMA Grafting

SI-ATRP NIPAAM PNIPAAM Grafting

ATRP MMA PMMA

ATRP MMA PMMA Grafting

ATRP PEGMA Grafting

from

lyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

[140,148]

lecular hydrogels, self-healing materials.

ATRP PEGMA Grafting

ATRP MMA PMMA

ATRP MMA PMMA Grafting

ATRP DAEAPDAEA Grafting

BMA PBMA

ATRP PEG-A; NIPAAM Grafting

ATRP NIPAAM PNIPAAM Grafting

Several techniques described in the review. Monomers copolymerized with natural ex-

ATRP PEG-A; NIPAAM Grafting

SI-ATRP NIPAAM PNIPAAM Grafting

SI-ATRP NIPAAM PNIPAAM Grafting

Several procedures described.

ATRP PEG-A; NIPAAM Grafting

BMA PBMA

Several techniques described in the review. Monomers copolymerized with natural ex-

ATRP MMA PMMA

tracts.

from

from

bide, butanediol.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

tracts.

from

Grafting from Grafting through

bide, butanediol.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

from

from

from

Grafting from Grafting

from

Grafting from

bide, butanediol.

from

from

Grafting from

from

Several procedures described.

Grafting from Grafting through

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

> Grafting from Grafting through

> > tracts.

Several techniques described in the review. Monomers copolymerized with natural ex-

Several techniques described in the review. Monomers copolymerized with natural ex-

and AA.

tracts.


temperature; Ionic responsive nanofibrous material. [140,145]

SI-ATRP NIPAAM PNIPAAM Grafting


analyzed by 1H NMR and GPC, using adequate solvents.

PMMA

which polymerized AM

**FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA,

**RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

analyzed by 1H NMR and GPC, using adequate solvents.

was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

Grafting from

which polymerized AM

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

analyzed by 1H NMR and GPC, using adequate solvents.

lowed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm

was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

[140]

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Thermoplastic elastomers. [140,144]

Grafting from Grafting through

> Grafting from Grafting through

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

analyzed by 1H NMR and GPC, using adequate solvents.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

tion, washing and drying. Grafting was measured using 1H NMR.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol. **ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

analyzed by 1H NMR and GPC, using adequate solvents.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

50 °C; Thermoresponsive material. [140,141]

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

[140]

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

**ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

Hydrophobic polymer composites. [140,142]

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

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

50 °C; Thermoresponsive material. [140,141]

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Backbone: Kraft lignin; Catalyst: CuBr/PMDETA; Solvent: water/DMF; T= 80 °C;

tion, washing and drying. Grafting was measured using 1H NMR.

Backbone: Organosolv lignin; Catalyst: CuBr/Me6TREN; Solvent: THF; T= 65 °C;

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The

Thermoplastic elastomers. [140,144]

analyzed by 1H NMR and GPC, using adequate solvents.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The

tion, washing and drying. Grafting was measured using 1H NMR.

Hydrophobic polymer composites. [140,142]

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

[140]

bide, butanediol.

Grafting from Grafting through

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

which polymerized AM

and AA.

which polymerized AM

and AA.

Several techniques described in the review. Monomers copolymerized with natural ex-

Several procedures described.

ATRP NIPAAM PNIPAAM Grafting

Several procedures described.

ATRP DAEAPDAEA Grafting

tracts.

which polymerized AM

which polymerized AM

and AA.

and AA.

and AA.

which polymerized AM

and AA.

which polymerized AM

ATRP PEG-A; NIPAAM Grafting

ATRP NIPAAM PNIPAAM Grafting

ATRP MMA PMMA

Several techniques described in the review. Monomers copolymerized with natural ex-

and AA.

which polymerized AM

Several techniques described in the review. Monomers copolymerized with natural ex-

ATRP MMA PMMA

Several procedures described.

BMA PBMA

lecular hydrogels, self-healing materials.

lecular hydrogels, self-healing materials.

lecular hydrogels, self-healing materials.

from

lyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

Backbone: Kraft lignin (alkali); Lignin-Br + PEGMA Lignin-g-PEGMA; Catalyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

from

from

ATRP PEGMA Grafting

lecular hydrogels, self-healing materials.

lecular hydrogels, self-healing materials.

lyst: CuBr/HMTETA; Solvent: Acetone; Room temperature, overnight; Supramo-

[140,148]

[140,148]

[140,148]

BMA PBMA

ATRP DAEAPDAEA Grafting

from

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

from

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

bide, butanediol.

tion, washing and drying. Grafting was measured using 1H NMR.

from

from

Grafting from

from

Grafting from Grafting through

tracts.

Several techniques described in the review. Monomers copolymerized with natural ex-



from

from

Backbone: Kraft lignin (alkali); Catalyst: CuBr/HMTETA.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

50 °C; Thermoresponsive material. [140,141]

ATRP PEG-A; NIPAAM Grafting

ATRP NIPAAM PNIPAAM Grafting

from

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

tion, washing and drying. Grafting was measured using 1H NMR.

*Processes* **2021**, *9*, x FOR PEER REVIEW 21 of 91

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

analyzed by 1H NMR and GPC, using adequate solvents.

0.2 g Lignin-g-Pam were dissolved in KOH solution (0.1 g in 1 mL of water), followed by heating (T= 70 °C, t= 12 hrs.), followed by neutralization with HCl. The solution was then precipitated into diethyl ether and dried in air. Ungrafted PAm was withdrawn by extraction with CH2Cl2. The product was vacuum dried, and

tion, washing and drying. Grafting was measured using 1H NMR.

98% in 24 h for both monomers. The product was obtained by precipitation, filtra-

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol. **ADMET (Acyclic Diene Metathesis Polymerization) and ROP:** Ferulic acid, isor-

analyzed by 1H NMR and GPC, using adequate solvents.

Backbone: Kraft lignin (alkali); Catalyst: CuBr/PMDETA; Solvent: water/DMF; T=

50 °C; Thermoresponsive material. [140,141]

[140]

[140]

bide, butanediol.

Monomers and polymers grafted by: **FRP:** Guaiacol-AM, Vainillin-LMA. **RAFT:** Syringyl methacrylate, STY, MMA, 4-propylsyringol, 4-propylguaiacol.

> Grafting from Grafting

which polymerized AM

and AA.

which polymerized AM

and AA.

Several techniques described in the review. Monomers copolymerized with natural ex-

Several procedures described.

ATRP NIPAAM PNIPAAM Grafting

Several procedures described.

Grafting from Grafting through

tracts.

Several techniques described in the review. Monomers copolymerized with natural ex-

tracts.

