Synthesis of chitin-graft-polystyrene via atom transfer radical polymerization initiated from a chitin macroinitiator

Abstract

In this study, we synthesized chitin-graft-polystyrene by graft polymerization of styrene from a chitin macroinitiator via atom transfer radical polymerization (ATRP). First, the chitin macroinitiators for ATRP were synthesized by acylation of chitin with 2-bromopropionyl bromide in 1-allyl-3-methylimidazolium bromide (AMIMBr) ionic liquid. Because the products, which were obtained from reactions using 20 and 30 equiv. of 2-bromopropionyl bromide per repeating unit of chitin, were soluble in DMSO, the degrees of substitution (DS) values were calculated by ¹H NMR measurement in DMSO-d₆ to be 1.66 and 1.86, respectively. Then, graft polymerization of styrene from the obtained chitin macroinitiator with DS = 1.86 was performed by ATRP using N,N,N′,N′′,N′′-pentamethyldiethylene triamine and CuBr as the catalytic system. The yields of the products increased with increasing the feed ratios of styrene to chitin macroinitiator initiating site. To estimate the M_n values of the grafted polystyrenes (PSs), furthermore, separation of the PS chains from the chitin main-chain was conducted using alkaline hydrolysis. Their GPC traces were monomodal and the M_n values calculated using polystyrene standards increased with increasing the feed ratios of styrene to initiating sites.