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

• Published in: Macromolecules 2012-08, Vol.45 (15), p.5923-5933
• Main Authors: Sanders, Gemma C, Duchateau, Robbert, Lin, Ching Yeh, Coote, Michelle L, Heuts, Johan P. A
• Format: Article
• Language: English
• Subjects: Applied sciences; Copolymerization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Preparation, kinetics, thermodynamics, mechanism and catalysts
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma301161u

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 transfer reaction, which is orders of magnitude faster than that of styrenic radicals. This conclusion was supported by high-level ab initio quantum chemical calculations, which showed that hydrogen abstraction from the maleic anhydride radical is 40 kJ/mol more exothermic than that from a styrene radical. The chain transfer constant of COBF was determined for the different ratios of styrene and α-methylstyrene. It was found to increase 2 orders of magnitude from a purely styrene–maleic anhydride to a purely α-methylstyrene–maleic anhydride copolymer. Diels–Alder and thiol–ene reactions were performed on the vinylic end groups as postpolymerization modification reactions, as well as graft copolymerization reactions of the macromonomers with styrene and butyl acrylate.