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Article

Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes

by
Sourita Jana
1,2,
Debasis Samanta
1,2,
Mir Muhammad Fahad
3,
Sellamuthu N. Jaisankar
1,2,3,* and
Hongdoo Kim
3,*
1
Polymer Science & Technology Division, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
2
University of Madras, Chennai 600005, India
3
Department of Advanced Materials Engineering for Information and Electronics, College of Engineering, Kyung Hee University, Yongin-si 17104, Korea
*
Authors to whom correspondence should be addressed.
Polymers 2021, 13(17), 2875; https://doi.org/10.3390/polym13172875
Submission received: 2 July 2021 / Revised: 24 July 2021 / Accepted: 27 July 2021 / Published: 27 August 2021
(This article belongs to the Section Polymer Chemistry)
Browse Figures
Versions Notes

Abstract

:
Diisocyanates, particularly toluene diisocyanate (TDI), are useful for the preparation of various polyurethanes with specific applications as leather-like materials, adhesives and insoles, etc. Blocking agents can be used for the operational simplicity and to reduce the hazards of TDI. In this paper, we reported the use of 3-(4-bromo-phenyl)-1H-pyrazole to block toluene diisocyanate (TDI). FTIR, NMR, thermogravimetric analysis, contact angle analysis and differential scanning calorimetry (DSC) were used for the characterization. The effectiveness of the blocking was confirmed by spectroscopic techniques. The DSC thermogram showed that blocked adducts deblock at 240 °C, causing the regeneration of TDI, and causing the diisocyanates to react with polyols of different molecular weights, forming polyurethanes. The characterization of the polyurethanes was performed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and a contact angle study.

1. Introduction

Polyurethanes are widely used for the manufacturing of jackets, shoe components and parts of furniture. Their flexibility, low glass transition temperature and high mechanical strength make them an attractive choice for the preparation of leather-like materials. In many cases, polyurethanes have hard segments as well as soft segments. In many cases, the soft segments which are generated from polyethylene glycol or polypropylene glycol can affect the glass transition temperatures, melting, or hydrophobicity. The choice of reagents, the process of preparations, or the surface morphologies are essential for the development of polyurethanes with better properties.
Polyurethanes are usually prepared by the step-growth polymerization of diisocianates and diols or polyols [1]. Because some of the diisocyanates are hazardous, they can be blocked with compounds with active hydrogen, so that they can be unblocked in the presence of diols to produce polyurethanes [2]. Very recently, different compounds have been used as blocking agents, such as pyrazoles and indoles, etc. [3]. Recently, 2-formyloxyethyl methacrylate, a liquid blocking agent, was used to block different isocyanates [4]. Likewise, 2,4-Toluene diisocyanate has been blocked with imidazole, 2-methylimidazole and 2-Phenyl-imidazole [5]. In this case, the addition of isocyanates with active hydrogen compounds like alcohols, amines and thiols, etc., leads to the formation of urethane, urea, thiourethane and amides. Among those, thiols react with isocyanates at a slower rate than alcohols and amines [6]. Phenol-, 2-naphthol- and 1-nitroso-2-naphthol were used as blocking agents to block toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI). The 2-naphthol-blocked diisocyanate adducts were thermally less stable than the phenol-blocked diisocyanates adducts. The introduction of the nitroso group in the blocking agent reduces the dissociation temperature. ε-caprolactam has been widely used as an effective blocking agent for isocyanates [7]. Polyisocyanates blocked with caprolactam represent a commercially important class of polyols. The dissociation temperature of a polyisocyanate blocked with ε-caprolactam ranges between 130 °C and 160 °C [8]. Further, malonate and oximes, etc., have been reported as blocking agents for isocyanates [9,10]. Sodium bisulfite-blocked isophorone diisocyanate is water soluble and stable for more than 12 months at room temperature, both in a liquid and solid state [11]. The blocking of polymethylene polyphenyl isocyanates (PAPI) had been acheived by using sodium bisulfate [12]. Among the different blocking agents, pyrazole-based blocking agents have attracted special attention because of their effectiveness in blocking as well as deblocking [13]. The deblocking reactions of pyrazole-blocked isocyanate proceed through a five-center complex formation [12,14]. In this context, a group of water-dispersible blocked polyisocyanates were synthesized from toluene 2,4-diisocyanate (TDI) and isophorone diisocyanate (IPDI) using ethyl cellosolve (EC), epsilon-caprolactam (CL) and methyl ethyl ketoxime (MEKO) as blocking agents in the presence of dimethylol propionic acid [15]. The aqueous dispersions of the adducts offer good storage stability. The initial deblocking temperatures of the adducts are about 55–85 °C. Furthermore, methyl anacardate, secondary butyl anacardate and cardanol-N-hydroxyphthalimide (NHPH) were separately used as blocking agents to block 2,4-toluene diisocyanate [16]. Aqueous polyurethane dispersions have been prepared from castor oil [17], and a polyurethane coating with better adhesion and anticorrosion protection, synthesized from blocked isocyanate, has been reported recently [18]. Along the line, toluene diisocyante (TDI), isophoronediisocyanate (IPDI), hexamethylenediisocyanate (HDI) and 4,4’-diphenylmethanediisocyanate (MDI) blocked with 2-butoxyethanol have been reported separately [19].
The efficacy of the formation of blocked isocyanate depends on the structures of the isocyanate and blocking agent, the thermal stability of the isocyanate-blocking agent bond, and catalysis [20]. Along the same line, isocyanates were blocked with methyl ethyl ketoxime (MEKO) and bisulfite (BS) for the fabrication of DNA microarrays [20]. Isocyanates like hexamethyelenediisocyanate, diphenylmethane diisocyanate and isophorone diisocyanate can also be blocked with diethylene glycol monobutyl ether [21]. Imidazole-blocked 2,4-toluene diisocyanate with polyethylene glycol has been synthesized and characterized with DSC, TGA, DMA and glass transition temperature [22]. Furthermore, alkyl-pyrazole has been studied as a blocking agent [23], and polyurethanes have been synthesized from 4-bromo-1H-pyrazole-blocked HMDI [13]; polyurethane composites with nanomaterials have been reported by our group recently [24,25,26,27].
Although blocked isocyanates are useful for their non-hazardous methods, the stability and environment-friendliness of polyurethane elastomers depends on the use of aromatic or aliphatic isocyanates and chain extenders like diols, triols and anddiamines [28]. Their recyclability and properties have been studied in a few cases [29]. Furthermore, the degradation of polyurethane elastomers can happen by photo-thermal, ozonolytic, hydrolytic, chemical, enzymatic, in-vivo/in-vitro oxidative, biological, and mechanical degradation [30]. Recently we reported that biodegradable polyurethane foam is used in footware to reduce waste [31]. In this context, thermogravimetric analysis (TGA) can be conveniently used for the study of thermal stability, such as the degradation temperatures and the stages of degradations of polyurethanes. On the other hand, differential scanning calorimetry (DSC) is usually used for the study of the glass transition temperatures of polyurethane in order to understand its flexibility or application potential at different temperatures. Along the same lines, the hydrophobicity of polyurethane films can be studied by contact angle meters using water droplets. In this case, droplets on more hydrophilic polyurethane will spread, resulting in the lowering of the contact angle, while more hydrophobic polyurethane can provide a higher contact angle, often resulting in the rolling out of the water droplet from the surface. Although chemical compositions are the main factors influencing hydrophobicity, high surface roughness can cause superior hydrophobicity.
In this paper, we reported an efficient method of blocking diisocyanates to prepare polyurethanes using biocompatible polyethylene glycol. Deblocking and polyurethane formations were performed in a simple operation without using any organic solvent. Furthermore, the thus-formed polyurethanes were studied using standard methods such as TGA, DSC and a contact angle meter (vide infra) for their practical usability. Finally, the polyurethanes were successfully used as coating agents to improve hydrophobicity.

2. Materials and Methods

Toluene diisocyanate, polyethylene glycol-400 (PEG-400), PPG-1000, PPG-2000 and PPG-3000 were purchased from Sigma-Aldrich, Bangalore, India; 4-(3-bromophenyl)-1H-pyrazole was purchased from TCI, Japan and dibutyltindilaurate (DBTDL) was purchased from FLUKA SG, India and used as received. Solvents like chloroform and hexane are purchased from Emparta ER and used after purification.
Toluene diisocyanate (TDI) was reacted with 3-(4-bromophenyl)-1H-pyrazole as a blocking agent to form blocked isocyanate adducts. NMR, IR, TGA and DSC were used to characterize the materials, and to investigate the deblocking temperature. At the deblocking temperature, regenerated toluene diisocyanate was reacted with polyols of different molecular weights to form polyurethane. Scheme 1 describes the blocking reactions of isocyanates with 3-(4-bromo-phenyl)-1H-pyrazole. Scheme 2 describes the reactions of blocked TDI with 3-(4-bromo-phenyl)-1H-pyrazole with polyols.

2.1. Synthetic Procedure of 4-(3-Bromophenyl)-1H-Pyrazole-Blocked Toluene Diisocyanate Adducts

In total, 4.48 × 10−4 mol (0.1 g) of the blocking agent and 2.24 mol (0.03 mL) of TDI were taken in a 50 mL single-necked round-bottomed flask along with porcelain beads and dissolved in 15 mL solvent. TDI was added with a micropipette. In total, 0.54 weight percent of Dibutyltin dilaurate was added with a micropipette using 0.001% DBTDL. A guard tube was attached to it and, after refluxing, the round-bottom flask was allowed to cool to room temperature. Then, the content of the round-bottom flask was reduced in volume and transferred to a beaker; hexane was added for precipitation and kept at room temperature, i.e., 28 °C. The precipitation was filtered, and it was washed with hexane and dried in an oven at 60 °C for 6 h. For purification, the adduct was dissolved in chloroform and precipitated with hexane at room temperature.

2.2. Synthetic Procedure for the Preparation of Polyurethane from 4-(3-Bromophenyl)-1H-Pyrazole-Blocked TDI Adducts

In total, 3.08 × 10−4 moles (0.19 g) of 3-(4-bromophenyl-1H-pyrazole-blocked-toluene-diisocyanates and 3.08 × 10−4 moles (0.307 g) polyethers were taken in a beaker with a narrow diameter and kept in an oven at a temperature of 240 °C for 4 h. After that, the beaker was taken out of the oven in cold conditions. Then, the sample was set in a soxhlet apparatus using 500 mL pet ether and heated for 5 h. Next, 4-(3-Bromophenyl)-1H-pyrazole-blocked TDI adduct was synthesized in different conditions such as different catalytic concentrations, solvents and reflux times, as described in Table 1; the reaction conditions of polyurethane synthesis are described in Table 2.

2.3. Spectroscopic and Thermal Analysis

A Nicolet Impact 400, USA spectrometer was used to record the FT-IR spectra. Before recording the compound spectra, the background spectrum was taken. 1H and 13C NMR spectra were taken with a CDCl3 solvent on a JEOL 500 MHz ECA instrument at room temperature. For the 13C NMR and DEPT-135, the spectroscopic studies were performed with an operating frequency of 106 MHz. The ppm unit is used to express the chemical shift. For the thermogravimetric analysis instrument, a Netzsch, Germany with the model name “STA 449 F3 Jupiter” was used with a heating rate of 15 °C/min, and the samples were run from 25 °C to 600 °C in an inert atmosphere. The gas flows for both the balance and samples were maintained using a nitrogen atmosphere. For the DSC analysis, a differential scanning calorimetry instrument from Netzsch with the model name “DSC 214 Polyma, Germny” was used. In the case of an organic sample, the heating rate was 10 °C/min and the temperature range was 25 °C to 300 °C. In the case of a polymer sample, the heating rate of the sample was 5 °C/min, and the temperature was from −35 °C to 280 °C. A contact angle meter version 8.0 from Holmarc, India mechatronics was used for the contact angle analysis.

3. Results

The reaction of TDI with 3-(4-bromophenyl)-1H-pyrazole provided the blocked adduct with a yield of 91%. Because DSC predicted the deblocking temperature at 240 °C, simultaneous polymerization was performed at this temperature. In the gelation time study, the trend was observed as TDI-PEG-400 adduct < TDI-PPG-1000~TDI-PPG-2000~TDI-PPG-3000. In case of the yield of polyurethane from 3-(4-bromophenyl)-1H-pyrazole–TDI, the trend followed as TDI-PEG-400 adduct > TDI-PPG-1000 adduct > TDI-PPG-2000 ~ TDI-PPG-3000.

3.1. NMR Analysis

Table 3 shows the NMR spectral data of the blocked adducts, and Figure 1 shows the 1H NMR and 13C NMR of 3-(4-bromophenyl)-1H-pyrazole-blocked TDI. Table 4 shows the NMR spectra of polyurethane from blocked TDI with 3-(4-bromophenyl)-1H-pyrazole. The NMR data supported the structures of the blocked adduct and polyurethanes (Table 3 and Table 4 and Figure 1 and Figure 2).

3.2. DEPT-135

Distortionless enhancement by polarization transfer (DEPT) has been used to separately identify the signals of methyl (CH3), methylene (CH2) and methine (CH). In DEPT spectra, methyl (CH3) and methyne (CH) carbons are up and methene (CH2) carbons are down. Table 5 represents the DEPT spectra of polyurethane from 3-(4-bromophenyl)-1H-pyrazole-blocked TDI. Figure 3 describes the DEPT-135 spectra of polyurethane.

3.3. FTIR Analysis

The FTIR spectra of the blocked TDI and polyurethanes are shown in Table 6. Figure 4 represents the FTIR spectra of polyurethane. The absence of a peak at 2250–2270 cm−1 in 3-(4-bromophenyl)-1H-pyrazole-blocked TDI implies that the isocyanate group is completely blocked by the blocking agent. The absence of a peak at 2250–2270 cm−1 in polyurethane implies that the isocyanate group is completely blocked in polyurethane. Figure 4 represents the FTIR spectra of TDI-PEG-400 4(a), TDI-PPG-1000 4(b), TDI-PPG-2000 4(c) and TDI-PPG-3000 4(d).

3.4. TGA Thermogram

The TGA thermograms show the starting point and ending point of the blocked isocyanates and polyurethanes that were synthesized from blocked TDI. Table 7shows the TGA thermogram data of the mentioned compounds, and Figure 5 shows the TGA thermogram of the mentioned compounds. While blocked isocyanates showed the start of their decomposition at 168 °C, all of the polyurethanes showed thermal stability above 200 °C. Furthermore, blocked isocyanates showed the endpoint of their decomposition at 264 °C, while all of the polyurethanes showed an extended range for decomposition above 400 °C. Furthermore, the majority of the compounds were decomposed above 500 °C after the formation of polyurethanes. Furthermore, while a mass loss up to 150 °C is less than 3% for blocked isocyanates, in most of the cases of polyurethanes, a mass loss of up to 3–5% was observed. This may be attributed to the water molecules physically absorbed by the polymers. The TGA thermogram shows that blocked TDI is stable up to 160 °C. Polyurethanes are stable up to between 200 °C and 240 °C.

3.5. DSC Thermogram

The DSC thermogram shows the deblocking behaviours of the blocked isocyanates and the thermal transitions of polyurethanes after deblocking followed by reactions with diols or polyols. As observed from Figure 6, while the deblocking temperature or melting was observed at 240 °C, the glass transitions were observed in the range of −30 to −40 °C. Interestingly, clear glass transitions were observed for polyurethanes derived from PPG 1000 and PPG 2000 in low temperatures, as was generally observed for other polyurethanes. This is usually attributed to the low crystallinity and flexibility of different chains.

3.6. Contact Angle Analysis

Table 8 shows the contact angle values of the polyurethanes. Figure 7 shows water droplets on surfaces coated with different polyurethanes. As observed from the figures and tables, the contact angle data indicated the generally hydrophilic natures of the polyurethanes. Furthermore, the hydrophilicity increased with an increase of the molecular weights of the PPGs. This may be attributed to the presence of more oxygen moieties and reduced roughness [31]. It was observed by several researchers that roughness induces hydrophobicity due to the possibility of the formation of air pockets.

4. Discussion

It was generally observed that the gel time increased as the molecular weight of the polyol increased, and that polyurethane from polyethylene glycol showed a better yield than polyurethane from polypropylene glycol. In the case of the gelation time, PEG-polyurethane has a lower gelation time than PPG-polyurethane. The 1H and 13C NMR and DEPT-135 data supported the structures of the blocked adduct and polyurethanes. Mechanistically, the blocking of diisocyanates happens by the initial reaction of isocyanates with amine to form the intermediate compound, which can further react with polyol to form polyurethanes. For the blocked adduct, in 1H NMR, the peaks for the aryl rings appeared between 7–8 ppm, while the peaks for the pyrazolyl rings appeared above 8 ppm. In 13C NMR, the characteristic peaks for aromatic protons appeared between 100 and 120 ppm, while the characteristic peaks for carbonyl carbon appeared at 150 cm−1. After deblocking to produce polyurethanes, the peaks for the blocking agent disappeared expectedly, while the other characteristic aromatic protons appeared between 7 and 8 ppm. Similarly, in 13C NMR, the characteristic peaks for aromatic rings appeared above 100 ppm. From FTIR, the absence of a peak at 2250–2270 cm−1 in 3-(4-bromophenyl)-1H-pyrazole-blocked TDI implies that the isocyanate group is completely blocked by the blocking agent. Furthermore, the absence of a peak at 2250–2270 cm−1 after deblocking in the presence of PEG or PPG formation implies the successful formation of polyurethane. The TGA thermogram showed that blocked TDI was stable up to 166 °C, and that the polyurethanes were stable up to between 200 °C and 240 °C. The DSC thermogram showed the deblocking behaviours of the blocked isocyanates, indicating that at 240 °C blocked TDI deblocks. Polyurethane shows different glass transition temperatures in which the polyurethanes changes from a glassy state to rubbery state. The contact angle data showed that all of the synthesized polyurethane compounds are hydrophilic.

5. Conclusions

Here, 3-(4-bromo-phenyl)-1H-pyrazole was successfully used to block toluene diisocyanate. Spectroscopic data such as 1H, 13C NMR, DEPT-135 and FTIR confirmed the structure of the blocked TDI and the polyurethane synthesized from those blocked TDI. This type of blocking is particularly important to conveniently handle toxic substrates like TDI. Furthermore, the blocked isocyanate is stable for up to one year. The deblocking and polyurethane formation are conveniently performed in solvent-free conditions. The contact angle analysis indicated the hydrophilic nature of polyurethane.

Author Contributions

Conceptualization, S.N.J.; Formal analysis, M.M.F.; Investigation, S.J. and D.S.; Project administration, H.K.; Resources, S.N.J.; Supervision, H.K.; Writing–original draft, S.J. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported under the framework of the Brain Pool Program managed by the Na-tional Research Foundation of Korea (Grant Number: 2020H1D3A2A01103375).

Institutional Review Board Statement

CSIR-CLRI communication number: A/2021/PLY/MLP/1578 was assigned by the KRC department of CLRI.

Acknowledgments

All authors acknowledge CATERS, CSIR-CLRI for the TGA sample analysis and Gayathi Varnakumar for the contact angle analysis. CSIR-CLRI communication number: A/2021/PLY/MLP/1578. This work was supported under the framework of the Brain Pool Program managed by the National Research Foundation of Korea (Grant Number: 2020H1D3A2A01103375).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Gite, V.V.; Mahulikar, P.P.; Hundiwale, D.G. Preparation and properties of polyurethane coatings based on acrylic polyols and trimer of isophorone diisocyanate. Prog. Org. Coat. 2010, 68, 307–312. [Google Scholar] [CrossRef]
  2. Sang, S.L.; Li, Y.Y.; Wang, K.J.; Tang, J.L. Application of blocked isocyanate in preparation of polyurethane(urea) elastomers. J. Polym. Sci. Part A Polym. Chem. 2021, 138, 50582. [Google Scholar]
  3. Sathiyaraj, S.; Shanavas, A.; Kumar, K.A.; Sathiyaseelan, A.; Senthilselvan, J.; Kalaichelvan, P.T.; Nasar, A.S. The first example of bis(indolyl)methane based hyperbranched polyurethanes: Synthesis, solar cell application and anti-bacterial and anti-oxidant properties. Eur. Polym. J. 2017, 95, 216–231. [Google Scholar] [CrossRef]
  4. Tassel, X.; Barbry, D.; Tighzert, L. A new blocking agent of isocyanates. Eur. Polym. J. 2000, 36, 1745–1751. [Google Scholar] [CrossRef]
  5. Nasar, A.S.; Jaisankar, S.N.; Subramani, S.; Radhakrishnan, G. Synthesis and Properties of Imidazole-Blocked Toluene Diisocyanates. J. Macromol. Sci. Part A Pure Appl. Chem. 1997, 34, 1237–1247. [Google Scholar] [CrossRef]
  6. Dyer, E.; Glenn, J.F.; Lendrat, E.G. The Kinetics of the Reactions of Phenyl Isocyanate with Thiols1. J. Org. Chem. 1961, 26, 2919–2925. [Google Scholar] [CrossRef]
  7. Shen, T.F.; Lu, M.G.; Liang, L.Y. Preparation and Properties of Non-ionic Polyurethane Crosslinkers from 2-Ethoxyethanol/epsilon-caprolactam-BlockedDiisocyanate. J. Macromol. Sci. Part A Pure Appl. Chem. 2012, 49, 611–618. [Google Scholar] [CrossRef]
  8. Bertoldo, M.; Cappelli, C.; Catanorchi, S.; Liuzzo, V.; Bronco, S. Understanding theAccelerating Effect of ε-Caprolactam on the Formation of Urethane Linkages. Macromolecules 2005, 38, 1385–1394. [Google Scholar] [CrossRef]
  9. He, Z.A.; Blank, W.J. Crosslinking with malonate blocked isocyanates and with melamine resins. J. Coat. Technol. 1999, 71, 85–90. [Google Scholar]
  10. Carter, J.W.; Pappas, S.P. A Novel Design Strategy for Blocked Isocyanates to Enhance Their Reactivity with Alcohols-Oxime Blocking-Agents Which Undergo Intramolecular Cyclization. J. Coat. Technol. 1992, 64, 29–36. [Google Scholar]
  11. Zhou, Z.; Lv, H.; Wang, X.; Ren, F.; Xu, W. Deblocking of the water-soluble isophorone diisocyanate blocked by sodium bisulfite and its application. J. Appl. Polym. Sci. 2013, 128, 597–599. [Google Scholar] [CrossRef]
  12. Nasar, A.S.; Subramani, S.; Radhakrishnan, G. Synthesis and properties of aromatic secondary amine-blocked isocyanates. J. Polym. Sci. Part A Polym. Chem. 1999, 37, 1815–1821. [Google Scholar] [CrossRef]
  13. Jana, S.; Ramar, P.; Samanta, D.; Jaisankar, S.N. Bromo-substituted blocked hexamethylene diisocyanate adduct: Synthesis, characterization and application toward polyurethane coating. J. Macromol. Sci. Part A Pure Appl. Chem. 2020, 58, 298–308. [Google Scholar] [CrossRef]
  14. Mulebach, A. Pyrazoles—A novel class of blocking agents for isocyanates. J. Polym. Sci. Part A Polym. Chem. 1994, 32, 753–765. [Google Scholar] [CrossRef]
  15. Shen, T.F.; Zhou, D.W.; Liang, L.Y.; Zheng, J.; Lan, Y.X.; Lu, M.G. Synthesis and Characterization of Reactive Blocked-Isocyanate Coupling Agents from Methyl Ethyl Ketoxime, Ethyl Cellosolve/epsilon-Caprolactam Blocked Aromatic and Aliphatic Diisocyanates. J. Appl. Polym. Sci. 2011, 122, 748–757. [Google Scholar] [CrossRef]
  16. Nasar, A.S.; Shrinivas, V.; Shanmugam, T.; Raghavan, A. Synthesis and deblocking of cardanol-and anacardate-blocked toluene diisocyanates. J. Polym. Sci. Part A Polym. Chem. 2004, 42, 4047–4055. [Google Scholar] [CrossRef]
  17. Zhang, Z.W.; Peng, P.P.; Wu, Q.Y.; Zhang, J.A.; Wu, M.Y.; Liu, J.Y.; Yang, J.J. Preparation and antibacterial properties of poly (hexamethylene guanidine hydrochloride) modified ionic waterborne polyurethane. Prog. Org. Coat. 2021, 156, 106246. [Google Scholar] [CrossRef]
  18. Zhang, F.Y.; Liu, W.Q.; Liang, L.Y.; Wang, S.; Shi, H.Y.; Xie, Y.K.; Yang, M.P.; Pi, K. The effect of functional graphene oxide nanoparticles on corrosion resistance of waterborne polyurethane. Colloids Surf. A Physicochem. Eng. Asp. 2020, 591, 124565. [Google Scholar] [CrossRef]
  19. Ahmad, I.; Zaidi, J.H.; Hussain, R.; Munir, A. Synthesis, characterization and thermal dissociation of 2-butoxyethanol-blocked diisocyanates and their use in the synthesis of isocyanate-terminated prepolymers. Polym. Int. 2007, 56, 1521–1529. [Google Scholar] [CrossRef]
  20. Delebecq, E.; Pascault, J.-P.; Boutevin, B.; Ganachaud, F. On the Versatility of Urethane/Urea Bonds: Reversibility, Blocked Isocyanate, and Non-isocyanate Polyurethane. Chem. Rev. 2013, 113, 80–118. [Google Scholar] [CrossRef]
  21. Ranjbar, Z.; Montazeri, S.; Nayini, M.M.R.; Jannesari, A. Synthesis and characterization of diethylene glycol monobutyl ether-Blocked diisocyanate crosslinkers. Prog. Org. Coat. 2010, 69, 426–431. [Google Scholar] [CrossRef]
  22. Shen, T.F.; Sun, Y.J.; Sun, C.F.; Lu, M.G. Preparation and Characterization of Polyurethane Bioadhesive from Hydroxyl-terminated Polylactide and Imidazole-blocked Isocyanate. Polym. Korea 2013, 37, 232–239. [Google Scholar] [CrossRef] [Green Version]
  23. Rolph, M.S.; Markowska, A.L.J.; Warriner, C.N.; O’Reilly, R.K. Blocked isocyanates: From analytical and experimental considerations to non-polyurethane applications. Polym. Chem. 2016, 7, 7351–7364. [Google Scholar] [CrossRef] [Green Version]
  24. Prakash, D.; Jaisankar, S.N. Thermoplastic poly(urethane-thiourethane) triblock copolymers with SWCNTs composite. Diamond Relat. Mater. 2019, 93, 34–41. [Google Scholar] [CrossRef]
  25. Murali, A.; Gurusamy-Thangavelu, S.A.; Jaisankar, S.N.; Mandal, A.B. Enhancement of the physicochemical properties of polyurethane-perovskite nanocomposites via addition of nickel titanate nanoparticles. RSC Adv. 2015, 5, 102488–102494. [Google Scholar] [CrossRef]
  26. Meera, K.M.S.; Sankar, R.M.; Paul, J.; Jaisankar, S.N.; Mandal, A.B. The influence of applied silica nanoparticles on a bio-renewable castor oil based polyurethanenanocomposite and its physicochemical properties. Phys. Chem. Chem. Phys. 2014, 16, 9276–9288. [Google Scholar] [CrossRef]
  27. Sankar, R.M.; Meera, K.S.; Mandal, A.B.; Jaisankar, S.N. Thermoplastic polyurethane/single-walled carbon nanotube composites with low electrical resistance surfaces. High Perform. Polym. 2013, 25, 135–146. [Google Scholar] [CrossRef]
  28. Mustapha, S.; Andou, Y. Enhancing Mechanical Properties of Polyurethane with Cellulose Acetate as Chain Extender. Fibers Polym. 2021. [Google Scholar] [CrossRef]
  29. Gu, L.; Wu, Q.Y. Recyclable bio-based crosslinked polyurethanes with self-healing ability. J. Appl. Polym. Sci. 2018, 135, 46272. [Google Scholar] [CrossRef]
  30. Xie, F.W.; Zhang, T.L.; Bryant, P.; Kurusingal, V.; Colwell, J.M.; Laycock, B. Degradation and stabilization of polyurethane elastomers. Prog. Polym. Sci. 2019, 90, 211–268. [Google Scholar]
  31. Mukherjee, M.; Gurusamy-Thangavelu, S.A.; Chelike, D.K.; Alagumalai, A.; Das, B.N.; Jaisankar, S.N.; Mandal, A.B. Biodegradable polyurethane foam as shoe insole to reduce footwear waste: Optimization by morphological physicochemical and mechanical properties. Appl. Surf. Sci. 2020, 499, 143966. [Google Scholar] [CrossRef]
Polymers 13 02875 sch001 550
Scheme 1. Blocking reactions of isocyanates with 3-(4-bromophenyl)-1H-pyrazole.
Scheme 1. Blocking reactions of isocyanates with 3-(4-bromophenyl)-1H-pyrazole.
Polymers 13 02875 sch001
Polymers 13 02875 sch002 550
Scheme 2. Reactions of 3-(4-bromo-phenyl)-1H-pyrazole-blocked-Toluene diisocyanate with polyols.
Scheme 2. Reactions of 3-(4-bromo-phenyl)-1H-pyrazole-blocked-Toluene diisocyanate with polyols.
Polymers 13 02875 sch002
Polymers 13 02875 g001 550
Figure 1. (A) 1H NMR and (B) 13C NMR of 3-(4-bromophenyl)-1H-pyrazole-blocked TDI.
Figure 1. (A) 1H NMR and (B) 13C NMR of 3-(4-bromophenyl)-1H-pyrazole-blocked TDI.
Polymers 13 02875 g001
Polymers 13 02875 g002 550
Figure 2. (A) 1H NMR spectrum of TDI-PPG-1000, (B) 1H NMR spectrum of TDI-PPG-2000, (C) 13C NMR spectrum of TDI-PEG-400 and (D) 13C NMR spectrum of TDI-PPG-2000.
Figure 2. (A) 1H NMR spectrum of TDI-PPG-1000, (B) 1H NMR spectrum of TDI-PPG-2000, (C) 13C NMR spectrum of TDI-PEG-400 and (D) 13C NMR spectrum of TDI-PPG-2000.
Polymers 13 02875 g002
Polymers 13 02875 g003 550
Figure 3. DEPT-135 spectra of (A) TDI-PPG-1000 and (B) TDI-PPG-2000.
Figure 3. DEPT-135 spectra of (A) TDI-PPG-1000 and (B) TDI-PPG-2000.
Polymers 13 02875 g003
Polymers 13 02875 g004 550
Figure 4. FTIR spectra of different polyurethanes formed from blocked isocyanates.
Figure 4. FTIR spectra of different polyurethanes formed from blocked isocyanates.
Polymers 13 02875 g004
Polymers 13 02875 g005 550
Figure 5. TGA thermogram of (a) TDI-PEG-400, (b) TDI-PPG-1000, (c) TDI-PPG-2000 and (d) TDI-PPG-3000; (e) blocked TDI.
Figure 5. TGA thermogram of (a) TDI-PEG-400, (b) TDI-PPG-1000, (c) TDI-PPG-2000 and (d) TDI-PPG-3000; (e) blocked TDI.
Polymers 13 02875 g005
Polymers 13 02875 g006 550
Figure 6. DSC thermogram of (a) blocked TDI, (b) PU-TDI-PPG-1000 (inset: two cycles), (c) PU-TDI-PPG-2000 and (d) PU-PPG-3000.
Figure 6. DSC thermogram of (a) blocked TDI, (b) PU-TDI-PPG-1000 (inset: two cycles), (c) PU-TDI-PPG-2000 and (d) PU-PPG-3000.
Polymers 13 02875 g006
Polymers 13 02875 g007 550
Figure 7. Water droplets on the coated surfaces for the determination of the contact angle of (a) PU-TDI-PPG-1000, (b) PU-TDI-PPG-2000, (c) PU-TDI-PPG-2000 and (d) blocked isocyanates.
Figure 7. Water droplets on the coated surfaces for the determination of the contact angle of (a) PU-TDI-PPG-1000, (b) PU-TDI-PPG-2000, (c) PU-TDI-PPG-2000 and (d) blocked isocyanates.
Polymers 13 02875 g007
Table
Table 1. Synthesis of 4-(3-bromophenyl)-1H-pyrazole-blocked TDI adduct.
Table 1. Synthesis of 4-(3-bromophenyl)-1H-pyrazole-blocked TDI adduct.
S. No.TDI
Gram
× 10−4		Blocking Agent (Gram)Adduct
(Gram)		SolventReflux Time (Hour)Catalyst DBTDL
(wt.%)		Yield (%)
1.3.90.100.13CHCl33.00.8591
2.3.90.100.12CHCl33.00.6585
3.3.90.100.12CHCl33.00.5088
4.3.90.100.11CHCl33.01.081
Table
Table 2. Reaction conditions of polyurethane from 4-(3-bromophenyl)-1H-pyrazole-blocked TDI adduct.
Table 2. Reaction conditions of polyurethane from 4-(3-bromophenyl)-1H-pyrazole-blocked TDI adduct.
S. No.Wt. of Blocked Adduct
(Gram)		PolyetherWt of Polyether (Gram ×
10−4)		PolyurethaneWt of Polyurethane GramYield
(%)		Temp. (°C)Gelation Time (h)
1.0.10PEG-4006.44TDI-PEG-4000.061952403
2.0.19PPG-10003.22TDI-PPG-10000.175342404
3.0.1PPG-20003.22TDI-PPG-20000.13322404
4.0.1PPG-30004.83TDI-PPG-30000.18322404
Table
Table 3. NMR spectra of the blocked adduct.
Table 3. NMR spectra of the blocked adduct.
Compound1H NMR (in ppm)13C NMR (in ppm)
Polymers 13 02875 i0012.43 (CH3-7), 6.69 (2 H-10), 7.51 (H-2, H-3), 7.51 (4 H-13), 7.71(4 H-14), 8.0 (H-5), 8.21 and 8.31 (2 H-11), 9.10 (2 N-H).16.93 (CH3-7), 108 (C-5), 127.18 (4 C-13), 130 (4 C-14), 152 (2 C-8).
Table
Table 4. NMR spectra of polyurethane from blocked TDIwith3-(4-bromophenyl)-1H-pyrazole.
Table 4. NMR spectra of polyurethane from blocked TDIwith3-(4-bromophenyl)-1H-pyrazole.
Compound1H NMR (in ppm)13C NMR (in ppm)
Polymers 13 02875 i0021.54, 1.19 (H-16), 2.11 (H-17), 2.24 (H-1), 3.65 (2H-13), 4.22 (2H-12), 6.97 (N-H-8), 7.42 (H-3), 7.57 (H-4), 7.69 (H-6), 8.00 (N-H-9).17.37 (C-1), 31.25 (C-17), 61.49 (C-16), 64.32 (C-14), 67.3 (C-15), 115 (C-6), 122 (C-4), 127 (C-2), 130.7–131.7 (C-7), 136–137 (C-5), 149 (C-10), 153 (C-11).
Polymers 13 02875 i0031.10 (H-15), 1.24 (H-12), 2.14 (H-1), 3.34 (H-14), 3.47 (H-13), 6.51 (H-9), 7.2 (H-3), 7.48 (H-4), 7.56 (H-6), 8.01 (H-8)17.28 (C-15, C-1), 29.64 (C-16), 72.8 (C-15), 73 (C-17), 75 (C-18), 127 (C-4, C-6), 131.8 (C-7, C-5).
Polymers 13 02875 i0041.15 (H-15), 1.23 (H-12), 2.06, 2.26 (C-1), 3.41 (2H-13), 3.55 (H-14), 7.51 (H-3, H-4), 7.65 (H-6), 8.09 (H-8, H-9).17.2 (C-15), 22.62 (C-1), 28.29 (C-12), 45 (C-16), 72.75 (C-17), 75 (C-18), 127 (C-4, C-6), 131 (C-7,C-5), 170 (C-10), 196 (C-11).
Polymers 13 02875 i0051.06 (H-16), 1.19 (H-12), 3.33 and 3.45 (2H-13), 4.12 (H-14), 7.45 (H-3, H-4), 7.54 (H-6), 8.01 (N-H-9).17.3 (C-1), 17.4 (C-12), 22 (C-16), 31 (C-17), 73, 127.28 (C-5, C-7), 131 (C-3,C-4, C-6).
Table
Table 5. DEPT-135 spectral data of polyurethane from 3-(4-bromophenyl)-1H-pyrazole-blocked TDI.
Table 5. DEPT-135 spectral data of polyurethane from 3-(4-bromophenyl)-1H-pyrazole-blocked TDI.
CompoundDEPT-135 (in ppm)
Polymers 13 02875 i00617.11 (up)[CH3-1], 61.28 (down)[CH2-14], 63.5 (down) [CH2-13], 77.72 (down) [CH2-16], 126.9 (up) [CH-3], 130.13 (up) [CH-4], 131.7 (up) [CH-6].
Polymers 13 02875 i00717.12 (up) [CH3-1], 17.4 (down) [CH3-12], 71.69 (down) [CH2-15], 72.88 (down) [CH2-17], 73.61 (down) [CH2-16], 127.29 (up) [CH-3], 130 (up) [CH-4], 131 (up) [CH-6].
Polymers 13 02875 i00817.79 (up) [CH3-12], 20.9 (up) [CH3 -1], 73.39 (down) [CH2-17], 75.43 (down) [CH2-15], 77.30 (up) [CH-7],127 (up) [CH-3, CH-4], 131.5 (up) [CH-6].
Polymers 13 02875 i00917.45 (up) [CH3-1, CH3-12], 73.33 (down [CH2-17], 74.95 (down) [CH2-16], 127.19 (up), [CH-3, CH-4], 131 (up) [CH-6].
Table
Table 6. FTIR spectral data of blocked TDI and the polyurethane from it.
Table 6. FTIR spectral data of blocked TDI and the polyurethane from it.
Compound−NH Stretch
(cm−1)		−NCO
Stretch
(cm−1)		−C=O Stretch
(cm−1)		CH Stretch
(cm−1)		C–N Stretch
(cm−1)		C–O− Stretch
(cm−1)		C−H Bending
(cm−1)
Blocked TDI3355-1730314312301000752
TDI-PEG-4003306-1730288012301081781
TDI-PPG-10003306-17302868–299212301093756
TDI-PPG-20003318-17302980–286812301081769
TDI-PPG-30003318-17302868–298012301093769
Table
Table 7. TGA thermogram of the mentioned compounds.
Table 7. TGA thermogram of the mentioned compounds.
CompoundStarting PointEnding Point
Blocked TDI168.95 °C (97.13%)264.48 °C (3.121%)
PU-TDI-PEG-400236.63 °C (93.47%)514.12 °C (14.95%)
PU-TDI-PPG-1000244.9 °C (95.46%)454.34 °C (68.80%)
PU-TDI-PPG-2000216.92 °C (96.06%)535.35 °C (30.35%)
PU-TDI-PPG-3000201.00 °C (97.31%)521.70 °C (14.27%)
Table
Table 8. Contact angle data of polyurethanes.
Table 8. Contact angle data of polyurethanes.
CompoundContact Angle
PU-TDI-PPG-100066.3°
PU-TDI-PPG-200056.7°
PU-TDI-PPG-300043.0°
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Jana, S.; Samanta, D.; Fahad, M.M.; Jaisankar, S.N.; Kim, H. Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes. Polymers 2021, 13, 2875. https://doi.org/10.3390/polym13172875

AMA Style

Jana S, Samanta D, Fahad MM, Jaisankar SN, Kim H. Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes. Polymers. 2021; 13(17):2875. https://doi.org/10.3390/polym13172875

Chicago/Turabian Style

Jana, Sourita, Debasis Samanta, Mir Muhammad Fahad, Sellamuthu N. Jaisankar, and Hongdoo Kim. 2021. "Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes" Polymers 13, no. 17: 2875. https://doi.org/10.3390/polym13172875

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