Cationic Ring-Opening Copolymerization of Cyclic Acetals and 1,3-Dioxolan-4-ones via the Activated Monomer Mechanism and Transacetalization Reaction

Abstract

Cationic ring-opening copolymerization of cyclic acetals and 1,3-dioxolan-4-ones (DOLOs) was examined with a particular focus on elucidating the polymerization mechanisms. Cationic copolymerization of 1,3-dioxepane and 5-methyl-1,3-dioxolan-4-one successfully proceeded with CF3SO3H as a protonic acid catalyst, yielding copolymers. The main portion of these copolymers exhibited number-average molecular weight values greater than 104 (except for oligomer peaks). Detailed structural analyses of the copolymers were performed by NMR spectrometry and electrospray ionization mass spectrometry. The result suggested that copolymerization occurs via an activated monomer mechanism involving the reaction of a hydroxy group and a proton-attached DOLO. In addition, acid-catalyzed transacetalization reactions with hemiformal chain ends and formal moieties most likely occurred during copolymerization, resulting in consecutive formal structures in the main chain.