NEW EPOXY-TERMINATED OLIGOESTERS - PRECURSORS TO TOTALLY BIODEGRADABLE NETWORKS

Two types of novel biodegradable epoxy resins, carrying cycloaliphatic-epoxy and glycidyl ester end-groups, have been synthesized from hydroxy-telechelic oligoesters. The cycloaliphatic-epoxy end-groups were based on either methyl cis-4-cyclohexene-2-(carboxylic acid)-1-carboxylate or 3-cyclohexene-1-carboxylic acid. These compounds were reacted with hydroxy-telechelic poly(epsilon-caprolactone-co-D,L-lactide) oligoesters, yielding cycloaliphatic-olefin-terminated oligomers. Conversion of the olefin to the epoxide groups was achieved using a phase transfer epoxidation with an inorganic peracid derived from the reaction of phosphoric acid, sodium tungstate, and hydrogen peroxide. Aliquat 336, a quaternary ammonium salt, acted as the phase transfer catalyst. Nearly theoretical conversion of hydroxy to epoxy end-groups was achieved in only one case, however, alternative variations of this method of synthesis show promise. To prepare glycidyl ester-terminated prepolymers, hydroxy-telechelic poly(epsilon-caprolactone) oligoesters were reacted with succinic anhydride, in 1,2 -dichloroethane with 1-methylimidazole as catalyst, resulting in (carboxylic acid) -terminated oligomers. After conversion of the end-groups to the potassium carboxylate salt by titration with methanolic KOH, the isolated salt was dried and reacted with epibromohydrin in acetonitrile at reflux, using an 18-C-6 crown ether as the phase transfer catalyst, thus preparing the (glycidyl ester) -telechelic prepolymer. Epoxide equivalent weights differed by 2.7-7.1% from the theoretical values. These cycloaliphatic-epoxide and glycidyl ester-terminated prepolymers may be crosslinked with anhydrides or amines, respectively, to produce totally bioabsorbable networks.