1. Introduction

As the most abundant biomaterial on earth, cellulose has received enormous attention due to its wide applications in different fields, such as packaging [1], drug delivery [2], cosmetics [3], textiles [4], membranes [5], bioengineering [6], and electronics [7]. Cellulose has some outstanding advantages, including low cost, nontoxicity, good mechanical properties, and excellent biodegradability and biocompatibility [8]. However, cellulose is lack of thermoplasticity and shows poor dimensional stability and crease resistance. Due to the high crystallinity and presence of a large amount of intra- and inter-molecular hydrogen bonding, cellulose is difficult to be dissolved in common solvents [9]. Different solvent systems have been proposed to dissolve cellulose, including N,N-dimethylacetamide (DMAc)/lithium chloride (LiCl) [10], dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride (TBAF) [11], N,N-dimethylformamide (DMF)/dinitrogen tetroxide (N2O4) [12], N-methyl morpholine-N-oxide (NMMO) [13], alkali/urea aqueous [14], and ionic liquids [15]. The existence of three hydroxyl groups in each anhydroglucose repeating unit makes cellulose an active material to develop various derivatives via etherification [16], esterification [17], amination [18], carboxylation [19], carbanilation [20], acetylation [21], grafting [22], sulfation [23], and silylation [24]. It is worth noting that the hydroxyl group in the 6 position of cellulose is most

reactive, followed by the hydroxyl groups at 2 and 3 positions. The degree of substitution (DS) indicated the substituted number of hydroxyl group in anhydroglucose unit (AGU).

1-allyl-3-methylimidazolium chloride (BMIMCl) or DMAc/LiCl solution [32–37] under homogeneous conditions. The solubility of cellulose-based macroinitiator is strongly related to the DS of acylation, which can be adjusted by the molar ratio of acylating agent/AGU and reaction time [35, 38–40]. Therefore, it is flexible and convenient to prepare cellulose graft copolymers with controlled grafting density. Different solvents have been utilized as the media to synthesize cellulose graft copolymers via ATRP, including DMF, DMSO, 1,4-dioxane, AMIMCl, and BMIMCl. Moreover, varied catalyst systems, such as copper(I) chloride/2,20

Cellulose-Based Thermoplastics and Elastomers via Controlled Radical Polymerization

bipyridine (CuCl/bpy), CuCl/tris(2-(dimethylamino)ethyl)amine) (CuCl/

pentamethyldiethylenetriamine (CuCl/PMDETA), CuBr/PMDETA, CuBr/ ethylenediamine, and CuBr/diethylenetriamine (CuBr/DETA), have been

reported to control the grafting polymerization initiated by cellulose macroinitiator. During polymerization, the attached bromine or chlorine groups on cellulose macroinitiators can undergo a reversible redox process with metal catalysts and thus form active radicals to react and propagate with monomers. The active radicals can capture the halide ions from the oxidized metal complex to form activators and dormant halide species which can be reactivated. When polymerization is finished, the resultant cellulose graft copolymer can be obtained by removing the metal

ATRP can be performed to synthesize different kinds of thermoplastics and elastomeric polymers due to its high tolerance. As displayed in Figure 2, a variety of vinyl and acrylate monomers, including methyl methacrylate (MMA) [33, 35, 37, 41–44], N-isopropylacrylamide (NIPAM) [45–48], 2-methacryloyloxyethyl phosphorylcholine (MPC) [32], styrene (St) [35, 42], n-butyl acrylate (BA) [44], tert-butyl acrylate (tBA) [49, 50], 4-vinylpyridine (4-VP) [49, 51], acrylamide

Monomers have been used to prepare cellulose graft copolymers via ATRP strategy in homogeneous conditions.

(AM) [40], 3-ethyl-3-methacryloyloxy-methyloxetane (EMO) [12], N,

Me6TREN), copper(I) bromide/bpy (CuBr/bpy), CuCl/N,N,N<sup>0</sup>

catalyst and precipitating into a poor solvent.

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

Figure 2.

37


,N″,N″-

Cellulose graft copolymers, which combine cellulose and grafted side chains in one macromolecule can open new opportunities toward developing novel bio-based materials with tunable properties. Cellulose graft copolymers can be achieved with grafting-to, grafting-through, and grafting-from strategies [25]. Among these methods, the grafting-from strategy is the most effective route for designing cellulose graft copolymers from thermoplastics to thermoplastic elastomers. Atom transfer radical polymerization (ATRP) [26, 27], reversible addition-fragmentation chain transfer (RAFT) [28, 29] polymerization, and nitroxide-mediated polymerization (NMP) [30, 31] are well-established controlled radical polymerizations (CRPs) that can be performed to prepare cellulose-based copolymers with welldefined structures and narrow molecular weight distributions in both heterogeneous and homogeneous conditions. This chapter summarizes recent advances that have been made in cellulose-based thermoplastics and elastomers from native cellulose via homogeneous CRPs.
