Characterization of 3- And 4-arm stars from reactions of poly(butyl acrylate) RAFT and ATRP precursors

The mechanism of the reversible addition-fragmentation chain transfer (RAFT) process using cumyl dithiobenzoate has been the subject of intense debate. In an attempt to shed more light into the side reactions that affect the rate, it was decided to study the butyl acrylate (BA) system since its intermediate radical has a greater lifetime than for the styrene system and, as such, has the greatest opportunity to form intermediate radical terminated products. The approach taken was to elucidate the polymeric products made from the polymerization of BA in the presence of RAFT agent using a combination of size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The approach was extended to analyze reactions of polyBA-Br (with the Br functionality at the polymer end group) with copper catalyst in the presence of polyBA-SC-(Ph)=S (dormant RAFT species). Three- and four-arm stars are clearly observed when PBA-Br is reacted with Cu(I) and Cu(0) in the presence of polyBA-RAFT. This is the first example of the synthesis of 4-arm stars through intermediate-intermediate radical termination. We postulated that this is due to the much slower fragmentation rate in the BA system in comparison to the styrene system.