Temperature Responsive Cellulose-graft-Copolymers via Cellulose Functionalization in an Ionic Liquid and RAFT Polymerization

摘要

Well-defined cellulose-graft-polyacrylamide copolymers were synthesized in a grafting-from approach by reversible addition—fragmentation chain transfer polymerization (RAFT). A chlorine moiety (degree of substitution DS(CI) ≈1.0) was introduced into the cellulose using 1-butyl-3-methylimidazolium chloride (BMIMC1) as solvent before being substituted by a trithiocarbonate moiety resulting in cellulose macro-chain transfer agents (cellulose-CTA) with DS(RAFT) of 0.26 and 0.41. Poly(N,N-diethylacrykmide) (PDEAAm) and poly(N-isopropylacrylamide) (PNIPAM) were subsequently grafted from these cellulose-CTAs and the polymerization kinetics, the molecular weight characteristics and the product composition were studied by nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and size exclusion chromatography of the polyacrylamides after cleavage from the cellulose chains. The number-average molecular weights, M_n, of the cleaved polymers ranged from 1100 to 1600 g mol~(-1) for PDEAAm (dispersity B = 1.4-1.8) and from 1200 to 2600 g mol~(-1) for PNIPAM (B = 1.7-2.1). The LCST behavior of the cellulose-graft-copolymers was studied via the determination of cloud point temperatures, evidencing that the thermoresponsive properties of the hybrid materials could be finely tuned between 18 and 26 °C for PDEAAm and between 22 and 26 °C for PNIPAM side chains.