End group analysis of styrene-butyl acrylate copolymers initiated with benzoyl peroxide by stepwise chemolysis-pyrolysis gas chromatography

•Stepwise chemolysis-pyrolysis GC was proposed.•End groups in St-BA copolymers prepared with benzoyl peroxide (BPO) were analyzed in detail.•Two types of end groups originating from BPO could be individually determined.•Benzoyloxy radicals were proved to preferentially contribute in initiation rather than phenyl radicals.

End groups in a series of styrene (St)-butyl acrylate (BA) copolymer samples (St:BA, 80:20 molar feed ratio) prepared through radical polymerization with various amounts (1.5-10 wt%) of benzoyl peroxide (BPO) as an initiator were characterized. Two types of end groups originated from the BPO initiator-benzoyloxy and phenyl terminal groups-were individually determined by stepwise chemolysis-pyrolysis gas chromatography (Py-GC) using a double-shot furnace pyrolyzer. In the first (chemolysis) step, the copolymer sample was mixed with tetramethylammonium hydroxide and introduced into the pyrolyzer at 250 °C for 10 min. During this step, the benzoyloxy terminal groups were selectively and quantitatively decomposed into methyl benzoate through the thermally assisted hydrolysis and methylation of ester linkages, which was clearly observed in the pyrogram. In the second step, the residual polymer sample was analyzed by ordinary Py-GC at 600 °C. In the observed pyrogram, benzene and C14H12 were separately detected as the key products reflecting the phenyl terminal groups among the various pyrolyzates of the polymer main chain. Based on the peak intensities of these characteristic products, the relative contents of both types of the end groups from BPO were estimated to be almost proportional to the feed amounts of BPO. Moreover, it was determined that the number of benzoyloxy end groups was roughly twice of that of the phenyl terminal groups.