Synthesis of polystyrene-based Y-shaped asymmetric star by the combination of ATRP/RAFT and its thermal and rheological properties

Abstract

A₂A′-type asymmetric stars and A₂B-type miktoarm star polymers were prepared by the combination of atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) using the designed initiator. The first step involved the preparation of linear polystyrene with a hydroxyl group (LPSOH) by ATRP using the synthesized initiator 4,4′-di(bromomethyl)benzhydrol. Styrene was polymerized in bulk at 110 °C in the presence of Cu(I)Br and 2,2′-bipyridyl (Bipy) as a catalytic system. Next, the hydroxyl group in the resulting LPSOH chains was esterified to obtain LPS containing thiocarbonylthio (LPSCS₂) chains. The last step consisted of growing the third PS chain or poly-(n-butyl acrylate) chain by RAFT. This methodology enabled us to synthesize A₂A′ triarm PS stars with asymmetry in the molar mass of their branches and A₂B stars with chemically different PS and PBA arms. It also provided us a facile way to synthesize Y-shaped polymers. The effects of the length of the backbone and branched chain on the thermal properties and the rheology of the synthesized asymmetric polystyrene were studied. This method provided a way to obtain well-defined polymers with fixed backbone but different branch length. On using this method grams of sample can be obtained for melt behavior study.