Synthesis and characterization of novel biodegradable thermoplastic elastomers

Abstract

Biodegradable Thermoplastic Elastomer (BTPE) has the potential uses as implantable devices due to the possibility to change its chemistry and structure, thus controlling its elasticity. It also has potential applications in the biomedical area, especially in the area of controlled drug delivery and tissue engineering. Most of currently available biodegradable thermoplastic elastomers are polyurethanes, which contain urethane linkages. These versatile polymers have been used as implant materials for over 20 years but when they biodegrade in the body, the diamines produced are highly toxic. Synthesizing BTPE using a triblock copolymer made of biocompatible monomer will eliminate this problem. This thesis presents the synthesis and characterization of novel biodegradable thermoplastic elastomers made of ε-caprolactone (CL), trimethylene carbonate (TMC), and L-lactide (LLA). Various A-B-A triblock copolymers (whereby B block is random copolymer of PCL and PTMC, and A block is PLLA) have been synthesized by varying their middle-block compositions as well as end-block amounts. Our study showed that the molar ratio of CL:TMC is the single most crucial parameter in determining the mechanical properties of the copolymers, along with the molar mass of the PLLA end-block. Retaining the same basic middle-block of PCL/PTMC copolymer, the PLLA end-segment crystallinity was disrupted to examine its effect on elastomeric behavior. 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. The increase in elasticity for triblock copolymers with PCL inside PLLA hard block has led us to do a more thorough characterization of these copolymers.