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(ε‐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(ε‐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.