Accelerating the rate of polyester hydrolytic degradation is of interest for numerous biomedical applications. Poly(ε-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) have been extensively studied as thermoplastic homo- and copolymers as well as PCL–PLLA blends. PCL–PLLA semi-interpenetrating networks (semi-IPNs) prepared with thermoplastic PLLA embedded in a cross-linked PCL diacrylate (PCL–DA) network were previously shown to exhibit uniquely accelerated degradation behavior that increased with PLLA content. Herein, their properties before and during degradation were further investigated to reveal the origin of this behavior and to better understand the semi-IPNs’ degradation mechanism. Initially, semi-IPNs exhibited restricted spherulite size and irregularity, as well as a phase-separated morphology and a PLLA-rich surface. Under accelerated conditions (1 M NaOH, 37 °C), degradation was revealed to be initiated in PLLA regions. It was also found that the PCL–DA cross-linking and PCL–PLLA phase separation played the largest roles in degradation rates and that semi-IPNs underwent faster rates of degradation than an analogous blend largely due to the reduced crystallinity of PCL–DA. Nonaccelerated conditions (PBS [pH = 7.4], 37 °C) up to 56 weeks, which had never before been studied for polyester semi-IPNs, revealed similar trends in degradation rates
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