Poly(alpha-alkyl gamma-glutamate)s of microbial origin: I. Ester derivatization of poly(gamma-glutamic acid) and thermal degradation

A series of poly(alpha -alkyl gamma -glutamate)s (PAAG-n with n = 1-10) wer e prepared from poly(gamma -glutamic acid) (PGGA) of microbial origin by a two-steps synthesis procedure. The poly(alpha -ethyl gamma -glutamate) was firstly obtained by esterification of PGGA and then transesterified with th e selected alkanol to obtain the corresponding PAAG-n. The modification rea ctions were found to occur without alteration of the original enantiomeric composition but with a significant reduction in molecular weight. The therm al degradation of PAAG-n was examined by thermogravimetric analysis combine d with IR and NMR spectroscopy. At low temperatures (< 300 degreesC) decomp osition was found to take place by depolymerization with releasing of the c orresponding alkyl pyroglutamate. Decarboxylation of PAAG-n to an unsaturat ed polyamide seemed to be the main process occurring at high temperatures ( 400-450 degreesC). (C) 2001 Elsevier Science Ltd. Ail rights reserved.