Macromolecules, Vol.49, No.12, 4462-4472, 2016
Ring-Opening Alternating Copolymerization of Epoxides and Dihydrocoumarin Catalyzed by a Phosphazene Superbase
3,4-Dihydrocoumarin (DHC), a six-membered phenolic lactone derived from natural resources, which does not undergo homopolymerization, was subject to ring-opening anionic copolymerization with several epoxides (ethylene oxide, propylene oxide, 1,2-butylene oxide, styrene oxide, and 2-ethylhexyl glycidyl ether) from a mono- or dialcohol catalyzed by a phosphazene superbase (t-BuP4). Spectroscopic analysis revealed that the products were aromatic poly(ether-ester)s with perfect alternating monomeric sequences, consisting of both linear alternating copolymers and cyclic ones with relatively lower molar masses caused by intramolecular transesterification reactions. The alternating copolymers showed good thermal stability and higher glass transition temperatures as compared with the homopolymers of the corresponding epoxides. The in situ initiator-activation and chain growth mechanism of the t-BuP4-catalyzed polymerization also allowed for copolymerization of DHC and epoxides from multifunctional initiators, such as 1,1,1-trihydroxymethylpropane and poly(4-hydroxystyrene), yielding nonlinear (star and graft) products with alternating copolymer arms or side chains.