Four-armed PCL-b-PDLA diblock copolymer: 1. Synthesis, crystallization and degradation

A series of four-armed poly(ε-caprolactone)-b-poly(d-lactic acid) diblock copolymers (4a-PCL-b-PDLA) with well controlled composition were synthesized. The effect of length of PCL and PDLA blocks on the crystallization and enzymatic/alkaline degradation was studied. It was found that the PDLA blocks have great influence on the crystallization of PCL blocks under two different crystallization conditions. The copolymers with shorter PDLA blocks showed faster degradation rate but different spherulite structures after enzymatic degradation or alkaline degradation. The morphological changes of spherulites depended on the PCL chains which were trapped inside or excluded from the spherulites of PDLA when the copolymer crystallized at 80 °C or 30 °C (i.e. above or lower the glass transition temperature of PDLA chains). The spherulite morphology and porous morphology of copolymer films after degradation were well discussed. This work revealed that the crystalline morphology and degradation rate of PCL-b-PDLA films could be well controlled by copolymer composition and confined crystallization of PCL chains within the previously formed lamellar stacks of PDLA.