Synthesis of biodegradable thermoplastic elastomers based on polyurethane

Abstract

Biodegradable thermoplastic elastomer based on polyurethanes (BTPU) were synthesized from random or triblock copolymers, with polycaprolactone (PCL) as one of the component in the soft segments (SS). 1,6-hexamethylene diisocyanate (HMDI) and 1,4-butanediol (BDO) served as hard segments (HS). These BTPU contained low HS contents (~8 wt. %). We aimed to develop novel BTPU with maximum strain > 500 % and strain recovery > 90 %. To understand the effect of soft block and hard block on elastomeric properties, in vitro degradation and toxicity of degradation products, various BTPU were synthesized and the characterization results were organized into 4 chapters. In Chapter 4, BTPU based on PCL-co-PLLA with various CL:LLA molar ratio were examined. The mechanical properties increased with increasing L-lactide (LLA) contents. In vitro degradation showed that BTPU followed bulk degradation model. In Chapter 5, physical crosslinks in the BTPU based on PCL-co-PLLA was controlled by varying SS molar mass and HS chain length. These BTPU contained 5 – 18 wt. % of HS (HMDI+BDO) contents. The increase in HS chain length resulted in BTPU with higher modulus and strength. Strain recovery of 90 % was successfully obtained from BTPU with PCL-co-PLLA 8000 Da. In Chapter 6, the investigation was focused on the effect of PCL crystallinity. BTPU based on CL and 1,3-trimethylene carbonate (TMC) copolymers were prepared. Semicrystalline BTPU were stronger and more extensible than amorphous BTPU. Increase TMC contents in the SS can contribute to improved backbone flexibility, but also resulted in lower degree of phase separation between HS-SS that hinders the strain recovery. 7 weeks of in vitro degradation suggested no significant degradation and chain scissions occurred.