Reverse thermo-responsive biodegradable shape memory-displaying polymers

This study introduces shape memory-displaying (SM), reverse thermo-responsive (RTR) biodegradable polymers consisting of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblocks, and polycaprolactone (PCL) segments. The interplay between their composition, morphology and mechanical properties and their SM and RTR behavior was investigated as the polymers degraded. HO-(CL)n-(PEO-PPO-PEO)-(CL)n-OH pentablocks were synthesized and chain extended using hexamethylene diisocyanate (HDI), whereby a range of PFCLn polyether ester urethanes were generated. The PCL blocks formed two different crystalline phases melting at different temperatures, one acting as the net-points and the other as the switching segments. PFCLn polymers displayed remarkable SM behavior, as revealed by their high Rf and Rr values, and RTR behavior, as demonstrated by the significantly higher water uptake levels they attained below their LCST as opposed to above the transition. The polymers retained their RTR behavior as they degraded over the period investigated, while a gradual enrichment in the PCL content was observed as degradation took place. PFCLn polymers retained their excellent SM properties throughout fifteen SM full cycles conducted over two months. The dual SM/RTR functionality of the polymers developed render them especially suitable for a diversity of applications, such as in drug delivery, robotics and sensors.