Crosslinked poly(ester anhydride)s based on poly(ε-caprolactone) and polylactide oligomers

Abstract

Resorbable poly(ester anhydride) networks based on e-caprolactone, L-lactide, and D,L-lactide oligomers were synthesized. The ring-opening polymerization of the monomers yielded hydroxyl telechelic oligomers, which were end-functionalized with succinic anhydride and reacted with methacrylic anhydride to yield dimethacrylated oligomers containing anhydride bonds. The degree of substitution, determined by 13C NMR, was over 85% for acid functionalization and over 90% for methacrylation. The crosslinking of the oligomers was carried out thermally with dibenzoyl peroxide at 120 °C, leading to polymer networks with glass-transition temperatures about 10°C higher than those of the constituent oligomers. In vitro degradation tests, in a phosphate buffer solution (pH 7.0) at 37°C, revealed a rapid degradation of the networks. Crosslinked polymers based on lactides exhibited high water absorption and complete mass loss in 4 days. In e-caprolactone-based networks, the length of the constituent oligomer determined the degradation: PCL5-AH, formed from longer poly(e-caprolactone) (PCL) blocks, lost only 40% of its mass in 2 weeks, whereas PCL10-AH, composed of shorter PCL blocks, completely degraded in 2 days. The degradation of PCL10-AH showed characteristics of surface erosion, as the dimensions of the specimens decreased steadily and, according to Fourier transform infrared, labile anhydride bonds were still present after 90% mass loss.