Triblock copolymers of ε-caprolactone, trimethylene carbonate, and L-lactide: effects of using random copolymer as hard-block.

A series of triblock copolymers comprising end block of PLLA modified with PCL, and random copolymer of PCL and PTMC as soft segment were synthesized. DSC data show that PCL disrupted the crystallinity of PLLA, making the hard block to be completely amorphous when the PCL content is 50%. Correspondingly, the addition of PCL into PLLA block enhances the elongation of the triblock considerably. With regards to the elasticity, however, creep test results show that adding PCL to PLLA block seems to reduce the "equilibrium" recovery, while cyclic test results shows that the instantaneous recovery increased significantly with more PCL inside PLLA block. It was also observed that the degradation rate of triblock with added PCL inside the PLLA was slower compared to triblock with pure PLLA hard block. Compared to biodegradable polyurethane, these polymers are expected to yield less harmful degradation products, and offer more variables for the manipulation of properties. These polymers are also processable from the melt at temperatures exceeding about 130 °C. We expect to use these polymers in a variety of applications, including stent coatings, fully-degradable stents and atrial septal defect occluders.