EPOXIDATION OF BACTERIAL POLYESTERS WITH UNSATURATED SIDE-CHAINS - III - CROSS-LINKING OF EPOXIDIZED POLYMERS

The vinyl groups in the pendant substituents of a series of (3-hydroxy octanoate-co-3-hydroxy-10-undecenoate)s, PHOUs, were completely conver ted into epoxide groups with m-chloroperbenzoic acid to produce a seri es of copolymers, xyoctanoate-co-3-hydroxy-10,11-epoxyundecenoate)s, P HOEs containing 5, 9, 14, and 22 mol % of epoxide repeating units. The epoxidized polymers were crosslinked by reactions with succinic anhyd ride, using 2-ethyl-4-methylimidazole as an initiator, at 90 degrees C during a period of 0.5-4 h. Mild conditions were used for the crossli nking reactions to prevent degradation or rearrangement reactions, and the extent of crosslinking was evaluated from the sol-gel content. Bo th T-g and gel content increased after crosslinking, depending upon th e amount of epoxide group in the initial PHOE sample. Kinetic paramete rs for the crosslinking reaction were determined by use of the Kissing er and the Ozawa methods. The activation energy (15.6-16.0 kcal/mol) f or the crosslinking reaction was the same for each sample, and the fre quency factors were of the same order of magnitude, regardless of epox ide group content in the PHOE. The values obtained from the Ozawa meth od were slightly higher than those obtained from the Kissinger method. (C) 1998 John Wiley & Sons, Inc.