Z-Protected Glutamic Acid-Based Biodegradable Thermoplastic and Thermosetting Polyesters: Synthesis and Characterization

Biodegradable polymers were formed from N-benzyloxycarbonyl-L-glutamic acid with the comono-mers ethylene glycol, diglycidyl ether of 1,4-butanediol, and diglycidyl ether of bisphenol A. The three polymers were a linear and a rosslinked heterochain polyester and a crosslinked polyester that contained aromatic units within its network chains. The thermoplastic resin and the soluble fractions for the thermo-setting resins were characterized by gel permeation chromatography. Conversions for carboxylic acid were determined by titrations. A quality, 22,000 molecular weight thermoplastic resin was formed. The two ther-mosets were cured past their gel points. Gelation analysis revealed that the relative rate constants for the sequential oxirane/ acid and alcohol/acid reactions were distinct. With diglycidyl ether of 1,4-butanediol, the ratio of the respective rate constants was 3; with diglycidyl ether of bisphenol A, the ratio approached 200. The resins hydrolyzed to monomers in the presence of lipase, but in the presence of a mixed microbial cul-ture, only the first two resins decayed to biomass, respiratory gases, and water. The third resin was inert during the period of observation. amino-protected glutamic acid; biodegradable polymers; gelation; polymer networks; polyester