Degradable shape-memory polymer networks from oligo[(L-lactide)-ran-glycolide]dimethacrylates

In this paper degradable shape-memory polymer networks synthesized from oligo[(L-lactide)-ran-glycolide] dimethaycrylates are introduced. The macrodimethacrylates are prepared via a two-step synthesis: hydroxy telechelic oligo[(L-lactide)- ran-glycolide]s with number average molecular weights M-n ranging from 1000 to 5700 g mol(-1) were synthesized by ring-opening polymerization from L,L-dilactide, diglycolide and ethylene glycol as initiator using dibutyltin oxide as the catalyst. These oligodiols are reacted with methacryloyl chloride resulting in terminal methacrylate groups. Crosslinking of macrodimethacrylates is performed under exposure to UV light without applying a photo initiator. The polymer networks obtained are transparent and hydrolytically degradable. While the mechanical properties at temperatures higher than T-g depend on crosslinking density, T-g is almost constant at about 55 degrees C. The shape-memory functionality of the amorphous polymer network was investigated by cyclic, thermomechanical tests under the systematic variation of different programming parameters. Good shape-memory properties with strain recovery rates close to 100% were obtained under stress-controlled programming. Under strain-controlled conditions, it needs to be considered that relatively high stresses can be generated during programming. Potential biomedical applications are intelligent implants or smart drug release systems.