Photocurable liquid biodegradable copolymers:: In vitro hydrolytic degradation behaviors of photocured films of coumarin-endcapped poly(ε-caprolactone-co-trimethylene carbonate)

Coumarin-endcapped tetrabranched liquid copolymers composed of epsilon-caprolactone and trimethylene carbonate (TMC), prepared using pentaerythritol or four-branched poly(ethylene glycol) (PEG) as an initiator, were ultraviolet irradiated to produce photocured solid biodegradable copolymers. The hydrolytic degradation behaviors of photocured films were determined from the weight loss of the films. The initial hydrolysis rate (determined for up to 24 h using a quartz crystal microbalance) was enhanced with aqueous solutions of higher pH. The hydrolysis rate in the early period of immersion was increased with an increase in TMC content, whereas that in the later period (week order) decreased with a increase in TMC content. This inverse relation of composition dependence on the hydrolysis rate between the early and late periods was discussed. Topological measurements using scanning electron microscopy and atomic force microscopy as well as depth profiles of the fluorescein-stained hydrolyzed layer showed that for the pentacrythritol-initiated copolymer, irrespective of copolymer composition, hydrolysis occurred at surface regions and surface erosion proceeded with immersion time. For PEG-based copolymers, both surface erosion and bulk degradation occurred simultaneously. The hydrolyzed surfaces became highly wettable with water and exhibited noncell adhesivity.