2.2 Reversible addition-fragmentation chain transfer (RAFT) polymerization

RAFT polymerization is an alternative method to synthesize well-defined and narrow distributed polymers with complex topological architectures by choosing a proper chain transfer agent (CTA). RAFT polymerization can be conducted without using any metal catalyst, and thus it is convenient and easy to purify the resultant polymers, which is the biggest advantage over ATRP. To date, only limited attention has been paid to cellulose graft copolymers through homogeneous RAFT polymerization in the literature [78–81]. The combination of cellulose and RAFT polymerization can provide new opportunities for graft copolymers, especially those that could not be synthesized directly via ATRP strategy. Recently, our group designed a novel cellulose-based macromolecular chain transfer agent by introducing a trithiocarbonate derivative with dodecyl as stabilizing group on cellulose backbone from Cell-BiB for the synthesis of Cell-g-P(BA-co-AM) copolymers as strong materials from thermoplastics to elastomers via RAFT polymerization [82]. As shown in Figure 5, the bromine groups on Cell-BiB can be substituted by reacting with 1-dodecanethiol, carbon disulfide (CS2), and triethylamine (TEA) in DMSO. This Cell-CTA is versatile and suitable for a lot of monomers, and the DS of Cell-CTA can be manipulated by changing the molar ratios of above chemical reagents. AM and BA were chosen as the rigid and soft segments in the grafted side chains. PAM can provide reversible physical network structure in the cellulose graft copolymers. The N▬H and C=O groups in AM units can form strong selfcomplementary hydrogen bonds, and they are distributed homogeneously in the polymer matrix, leading to the strong and tough elastomer materials. Inspired by this work, we propose that high-performance cellulose graft copolymer can be

Cellulose-Based Thermoplastics and Elastomers via Controlled Radical Polymerization DOI: http://dx.doi.org/10.5772/intechopen.89436

Figure 5.

(N-isopropylacrylamide) (PNIPAM) [45–48], poly(4-vinylpyridine) (P4VP) [51], poly(N,N-dimethylamino-2-ethyl methacrylate) (PMDAEMA) [34], and poly(2-

(a) Schematic illustration of the synthesis of Cell-g-PI by ATRP and (b) fabrication of Cell-g-PI core-shell

nanoparticles with a PI core and cellulose shell (adapted with permission from Ref. [36]).

2.2 Reversible addition-fragmentation chain transfer (RAFT) polymerization

copolymers. The N▬H and C=O groups in AM units can form strong selfcomplementary hydrogen bonds, and they are distributed homogeneously in the polymer matrix, leading to the strong and tough elastomer materials. Inspired by this work, we propose that high-performance cellulose graft copolymer can be

RAFT polymerization is an alternative method to synthesize well-defined and narrow distributed polymers with complex topological architectures by choosing a proper chain transfer agent (CTA). RAFT polymerization can be conducted without using any metal catalyst, and thus it is convenient and easy to purify the resultant polymers, which is the biggest advantage over ATRP. To date, only limited attention has been paid to cellulose graft copolymers through homogeneous RAFT polymerization in the literature [78–81]. The combination of cellulose and RAFT polymerization can provide new opportunities for graft copolymers, especially those that could not be synthesized directly via ATRP strategy. Recently, our group designed a novel cellulose-based macromolecular chain transfer agent by introducing a trithiocarbonate derivative with dodecyl as stabilizing group on cellulose backbone from Cell-BiB for the synthesis of Cell-g-P(BA-co-AM) copolymers as strong materials from thermoplastics to elastomers via RAFT polymerization [82]. As shown in Figure 5, the bromine groups on Cell-BiB can be substituted by reacting with 1-dodecanethiol, carbon disulfide (CS2), and triethylamine (TEA) in DMSO. This Cell-CTA is versatile and suitable for a lot of monomers, and the DS of Cell-CTA can be manipulated by changing the molar ratios of above chemical reagents. AM and BA were chosen as the rigid and soft segments in the grafted side chains. PAM can provide reversible physical network structure in the cellulose graft

(diethylamino)ethyl methacrylate) (PDEAEMA) [56].

Figure 4.

Thermosoftening Plastics

40

Illustrations for the synthesis of Cell-CTA, Cell-g-P(BA-co-AM) copolymer, and the self-complementary hydrogen bonding in the cellulose graft copolymer (adapted from Ref. [82]).

accessed by introducing other supramolecular interactions into the matrix as reversible physical networks, such as metal-ligand coordination, π-π stacking, and host-guest complexation.

## 2.3 Nitroxide-mediated polymerization (NMP)

NMP is the first and easiest CRP technology controlled by a reversible termination mechanism between the nitroxide moieties and growing propagating macroradicals. A wide range of monomers, including acrylates, styrene derivatives, vinylpyridines, acrylonitrile, acryl acid, acrylamide derivatives, cyclic ketene acetals, and miscellaneous, can be polymerized via NMP to develop well-defined polymers [31]. The primary advantage of NMP is the absence of post-treatment since no catalyst or bimolecular exchange is needed during the polymerization. However, the higher polymerization temperatures and lower polymerization rates limit the wide applications of NMP. To the best of our knowledge, only one study reported the synthesis of cellulose graft copolymers through homogeneous NMP strategy started from microcrystalline cellulose [83]. In this work, pretreated cellulose was dispersed in anhydrous tetrahydrofuran and reacted with 2-bromoisobutyryl bromide and pyridine to prepare Cell-BiB. As shown in Figure 6, Cell-BiB could react with 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) in DMF in the presence of sodium hydride (NaH) to obtain functionalized cellulose (Cell-TEMPOL). At first, PS was grafted from cellulose backbone with Cell-TEMPOL as macroinitiator in the absence of any catalyst to produce Cell-g-PS. Cell-g-(PMMAb-PS) copolymer was synthesized by chain extension of above Cell-g-PS via the second NMP. Such kind of cellulose graft block copolymers may be applied as reinforcing agents, packing materials, and membrane materials. More efforts can be

backbone, the grafting density (the average number of grafts per anhydroglucose unit), the degree of polymerization, and distribution of grafts. Various block and random copolymers have been grafted from cellulose via CRPs as described above. However, as exhibited in Figure 7a, heterograft and graft-on-graft architectures with cellulose as backbone remain unreported, and these interesting graft copolymers can be synthesized by the combination of RAFT polymerization and ATRP, ring-opening polymerization (ROP) and ATRP or ROP and RAFT polymerization. Due to the increased attention paid on biomass-derived thermoplastics and elastomers, it becomes necessary and desirable to explore new monomers, which can be synthesized from bioresources, including lignins, terpenes, plant oils, rosin acids, and coumarins. For instance, bioresources, 7-hydroxyl-4-methylcoumarin, vanillin, guaiacol, and oleyl alcohol, can be used to synthesize sustainable monomers by reacting with acryloyl chloride, methacryloyl chloride or methacrylate anhydride as shown in Figure 7b. Among these monomers, 7-acryloyloxy-4 methylcoumarin (AMC), 7-methacryloyloxy-4-methylcoumarin (MMC), acrylated

Cellulose-Based Thermoplastics and Elastomers via Controlled Radical Polymerization

DOI: http://dx.doi.org/10.5772/intechopen.89436

vanillin (AV), methacrylated vanillin (MV), acrylated guaiacol (AG), and

Figure 7.

43

derived from different bioresources.

methacylated guaiacol (MG) can be utilized as rigid segments, while oleyl acrylate (OA) and oleyl methacrylate (OM) can be utilized as soft segments in the graft copolymers. Though there has been considerable progress, it is still challenging to

(a) Heterograft and graft-on-graft architectures of cellulose graft copolymers. (b) Sustainable monomers

#### Figure 6.

Schematic illustration for the synthesis of Cell-g-PS and Cell-g-(PMMA-b-PS) copolymers through NMP technique.

made in the future by grafting functional block polymers from cellulose via NMP to design novel stimuli-responsive hybrid materials with excellent macroscopic mechanical properties.

## 3. Perspective

CRPs are versatile and robust techniques to develop well-defined cellulose graft copolymers as novel thermoplastic and elastomers with desired properties for particular application demands. As the most adopted technique for cellulose graft copolymers, conventional ATRP suffers from the limitation of removing metal catalysts from the resultant products, which may cause undesired toxicity and coloration. Recently, new advances in ARTP have been reported, and metal-free ATRP has been developed to synthesize narrowly distributed polymers with welldefined structures by using photoredox organic catalysts under light irradiation instead of metal catalysts [84–86]. This new strategy can greatly promote the design and preparation of cellulose graft copolymers for different application fields. Cellulose graft copolymers show improved properties compared to the linear counterparts due to their unique molecular architectures, and the macroscopic performance of cellulose graft copolymers is affected by the degree of polymerization of cellulose

### Cellulose-Based Thermoplastics and Elastomers via Controlled Radical Polymerization DOI: http://dx.doi.org/10.5772/intechopen.89436

backbone, the grafting density (the average number of grafts per anhydroglucose unit), the degree of polymerization, and distribution of grafts. Various block and random copolymers have been grafted from cellulose via CRPs as described above. However, as exhibited in Figure 7a, heterograft and graft-on-graft architectures with cellulose as backbone remain unreported, and these interesting graft copolymers can be synthesized by the combination of RAFT polymerization and ATRP, ring-opening polymerization (ROP) and ATRP or ROP and RAFT polymerization.

Due to the increased attention paid on biomass-derived thermoplastics and elastomers, it becomes necessary and desirable to explore new monomers, which can be synthesized from bioresources, including lignins, terpenes, plant oils, rosin acids, and coumarins. For instance, bioresources, 7-hydroxyl-4-methylcoumarin, vanillin, guaiacol, and oleyl alcohol, can be used to synthesize sustainable monomers by reacting with acryloyl chloride, methacryloyl chloride or methacrylate anhydride as shown in Figure 7b. Among these monomers, 7-acryloyloxy-4 methylcoumarin (AMC), 7-methacryloyloxy-4-methylcoumarin (MMC), acrylated vanillin (AV), methacrylated vanillin (MV), acrylated guaiacol (AG), and methacylated guaiacol (MG) can be utilized as rigid segments, while oleyl acrylate (OA) and oleyl methacrylate (OM) can be utilized as soft segments in the graft copolymers. Though there has been considerable progress, it is still challenging to

Figure 7.

(a) Heterograft and graft-on-graft architectures of cellulose graft copolymers. (b) Sustainable monomers derived from different bioresources.

made in the future by grafting functional block polymers from cellulose via NMP to design novel stimuli-responsive hybrid materials with excellent macroscopic

Schematic illustration for the synthesis of Cell-g-PS and Cell-g-(PMMA-b-PS) copolymers through NMP

CRPs are versatile and robust techniques to develop well-defined cellulose graft copolymers as novel thermoplastic and elastomers with desired properties for particular application demands. As the most adopted technique for cellulose graft copolymers, conventional ATRP suffers from the limitation of removing metal catalysts from the resultant products, which may cause undesired toxicity and coloration. Recently, new advances in ARTP have been reported, and metal-free ATRP has been developed to synthesize narrowly distributed polymers with welldefined structures by using photoredox organic catalysts under light irradiation instead of metal catalysts [84–86]. This new strategy can greatly promote the design and preparation of cellulose graft copolymers for different application fields. Cellulose graft copolymers show improved properties compared to the linear counterparts due to their unique molecular architectures, and the macroscopic performance of cellulose graft copolymers is affected by the degree of polymerization of cellulose

mechanical properties.

Thermosoftening Plastics

3. Perspective

42

Figure 6.

technique.

achieve breakthroughs for the development of cellulose graft copolymers with ultra-strong mechanical properties comparable to commercial petroleum-based products. The marriage of cellulose and novel bio-based monomers via CRPs can provide a variety of opportunities for sustainable materials ranging from thermoplastics to elastomers, and these fascinating materials can find a pyramid of applications in our daily life in the near future.

References

9424-8

[1] Spence KL, Venditti RA, Rojas OJ, Habibi Y, Pawlak JJ. The effect of chemical composition on microfibrillar cellulose films from wood pulps: Water interactions and physical properties for packaging applications. Cellulose. 2010; 17:835-848. DOI: 10.1007/s10570-010-

DOI: http://dx.doi.org/10.5772/intechopen.89436

cellulose nanofibril paper. Nature Communications. 2015;6:7170. DOI:

[8] Moon RJ, Martini A, Nairn J, Simonsen J, Youngblood J. Cellulose nanomaterials review: Structure, properties and nanocomposites. Chemical Society Reviews. 2011; 40:3941-3994. DOI: 10.1039/

[9] Zhang X, Mao YM, Tyagi M, Jiang F, Henderson D, Jiang B, et al. Molecular partitioning in ternary solutions of cellulose. Carbohydrate Polymers. 2019;

[10] Araki J, Kataoka T, Katsuyama N,

preliminary study for fiber spinning of mixed solutions of polyrotaxane and cellulose in a dimethylacetamide/ lithium chloride (DMAC/LiCl) solvent system. Polymer. 2006;47:8241-8246. DOI: 10.1016/j.polymer.2006.09.060

Nordstierna L, Holmberg K, Nydén M. Dissolution and gelation of cellulose in TBAF/DMSO solutions: The roles of fluoride ions and water. Biomacromolecules. 2009;10:

2401-2407. DOI: 10.1021/bm900667q

[12] Philipp B, Nehls I, Wagenknecht W,

spectroscopic study of the homogeneous sulphation of cellulose and xylan in the N2O4-DMF system. Carbohydrate Research. 1987;164:107-116. DOI: 10.1016/0008-6215(87)80123-4

[13] Rosenau T, Potthast A, Sixta H, Kosma P. The chemistry of side reactions and byproduct formation in the system NMMO/cellulose (Lyocell process). Progress in Polymer Science. 2001;26:1763-1837. DOI: 10.1016/

S0079-6700(01)00023-5

220:157-162. DOI: 10.1016/j.

Teramoto A, Ito K, Abe K. A

[11] Ostlund Å, Lundberg D,

Schnabelrauch M. 13C-NMR

carbpol.2019.05.054

10.1038/ncomms8170

c0cs00108b

Cellulose-Based Thermoplastics and Elastomers via Controlled Radical Polymerization

[2] Amin MCIM, Ahmad N, Halib N, Ahmad I. Synthesis and characterization of thermo- and pH-responsive bacterial cellulose/acrylic acid hydrogels for drug delivery. Carbohydrate Polymers. 2012;

88:465-473. DOI: 10.1016/j.

[3] Ullah H, Santos HA, Khan T. Applications of bacterial cellulose in food, cosmetics and drug delivery. Cellulose. 2016;23:2291-2314. DOI: 10.1007/s10570-016-0986-y

[4] Forsman N, Lozhechnikova A, Khakalo A, Johansson LS, Vartiainen J, Österberg M. Layer-by-layer assembled hydrophobic coatings for cellulose nanofibril films and textiles, made of polylysine and natural wax particles. Carbohydrate Polymers. 2017;173:

392-402. DOI: 10.1016/j. carbpol.2017.06.007

311-322. DOI: 10.1016/j. carbpol.2015.06.041

45

[5] Livazovic S, Li Z, Behzad AR, Peinemann KV, Nunes SP. Cellulose multilayer membranes manufacture with ionic liquid. Journal of Membrane Science. 2015;490:282-293. DOI: 10.1016/j.memsci.2015.05.009

[6] Zhang QL, Lin DQ, Yao SJ. Review on biomedical and bioengineering applications of cellulose sulfate. Carbohydrate Polymers. 2015;132:

[7] Jung YH, Chang TH, Zhang HL, Yao CH, Zheng QF, Yang VW, et al. High-performance green flexible electronics based on biodegradable

carbpol.2011.12.022
