Synthesis of heteroarm star-shaped (polystyrene)n-[poly(ethyl acrylate)]m via atom transfer radical polymerization

Heteroarm star-shaped polymer, (polystyrene)n-[poly(ethyl acrylate)]m [(PS)n-(PEA)m], was synthesized in three steps. In the first step, star-shaped polystyrene, (PS)n, was synthesized by the arm-first method via atom transfer radical polymerization (ATRP) using a preformed PS macroinitiator, which was obtained by ATRP of styrene with ethyl 2-bromoisobutyrate as the initiator, in the presence of divinyl benzene (DVB). In the microgel core of (PS)n, there were not only a number of active initiating sites for ATRP, but also some unreacted vinyl groups. Then, in the second step, the residual vinyl groups were converted to 1-bromoethylbenzene groups by hydrobromination. In the last step, heteroarm star-shaped polymer, (PS)n-(PEA)m, where the arm number of PEA was greater than that of PS, was prepared by ATRP of ethyl acrylate using the hydrobrominated (PS)n as the macroinitiator from 1-bromoethylbenzene initiating sites, obtained by both the addition of linear PS macroinitiators to vinyl groups of DVB and the hydrobromination of residual vinyl groups.