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

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 Mn 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 Mn values calculated using polystyrene standards increased with increasing the feed ratios of styrene to initiating sites