Epoxidation of bacterial polyesters with unsaturated side chains. III. Crosslinking of epoxidized polymers

Abstract

The vinyl groups in the pendant substituents of a series of poly(3-hydroxyoctanoate-co-3-hydroxy-10-undecenoate)s, PHOUs, were completely converted into epoxide groups with m-chloroperbenzoic acid to produce a series of copolymers, poly(3-hydroxyoctanoate-co-3-hydroxy-10,11-epoxyundecenoate)s, PHOEs containing 5, 9, 14, and 22 mol % of epoxide repeating units. The epoxidized polymers were crosslinked by reactions with succinic anhydride, using 2-ethyl-4-methylimidazole as an initiator, at 90°C during a period of 0.5-4 h. Mild conditions were used for the crosslinking reactions to prevent degradation or rearrangement reactions, and the extent of crosslinking was evaluated from the sol-gel content. Both T g and gel content increased after crosslinking, depending upon the amount of epoxide group in the initial PHOE sample. Kinetic parameters for the crosslinking reaction were determined by use of the Kissinger and the Ozawa methods. The activation energy (15.6-16.0 kcal/mol) for the crosslinking reaction was the same for each sample, and the frequency factors were of the same order of magnitude, regardless of epoxide group content in the PHOE. The values obtained from the Ozawa method were slightly higher than those obtained from the Kissinger method.