End-Functional Styrene–Maleic Anhydride Copolymers via Catalytic Chain Transfer Polymerization

Styrene–maleic anhydride copolymers have been successfully synthesized using catalytic chain transfer polymerization employing the low spin [bis(difluoroboryl)dimethylglyoximato]cobalt(II) (COBF) complex. By partially replacing styrene with α-methylstyrene (while maintaining the amount of maleic anhydride at 50 mol %) over a range of ratios, it was shown that the rate of reaction and molar mass decreases with increasing α-methylstyrene content. The polymers were characterized using MALDI–ToF–MS and 1H–13C gHMQC NMR to determine the end groups, which in the presence of α-methylstyrene was an α-methylstyrene unit with a vinylic functionality. For styrene–maleic anhydride copolymers, the end group was determined to be predominantly maleic anhydride with a vinylic functionality. Considering the fact that in a styrene–maleic anhydride copolymerization the propagating radicals are predominantly of a styrenic nature, this was a very surprising result, suggesting that the maleic anhydride radicals undergo a chain...