Cationic Ring-Opening Polymerization of Cyclic Carbonates with Alkyl Halides To Yield Polycarbonate without the Ether Unit by Suppression of Elimination of Carbon Dioxide

Abstract

Cationic ring-opening polymerization of cyclic carbonates with alkyl halide as initiator during which no decarboxylation takes place is described in detail, using 5,5-dimethyl-1,3-dioxan-2-one (1), 1,3-dioxan-2-one (2), 5-n-butyl-1,3-dioxan-2-one (5), and 1,3-dioxaspiro[5.5]undecan-2-one (6) as monomers. Cationic polymerizations of 2, 5, and 6 with cationic initiators such as methyl triflate and boron trifluoride etherate were carried out under various conditions. In the polymerizations decarboxylation (elimination of carbon dioxide) during the polymerization occurred to yield the corresponding polycarbonate with ether units (5−10%) in the main chain. 6 only gave a small amount of polymer. Prolonged reaction time and enhanced temperature accelerated the decarboxylation. Reactions of the polycarbonate of 2 with several cationic initiators including methyl iodide were monitored by 1H NMR and gel permeation chromatography. Both a decrease in the polymer molecular weight and an increase in the ratio of ether ...