One-way and reversible dual-shape effect of polymer networks based on polypentadecalactone segments

A series of degradable polymer networks containing poly(omega-pentadecalactone) (PPD) switching segments showing a thermally-induced shape-memory effect were synthesized by co-condensation of PPD-macrotriols or -tetrols with an aliphatic diisocyanate. Thermal and mechanical properties at different temperatures were explored for polymer networks as a function of crosslink density by varying the polymer chain segment length or the netpoint functionality. All polymer networks exhibited excellent shape-memory properties with shape recovery rates R(r) between 99% and 100% determined in the 5th cycle under stress-free conditions. Furthermore, the polymer networks were capable of a reversible dual-shape effect based on crystallization induced elongation (CIE) and melting-induced contraction (MIC) in cyclic, thermomechanical experiments under constant stress. In these tests, the polymer networks were capable of a shape-change of 130% elongation. The associated temperatures at which CIE or MIC occurred (T(CIE) and T(MIC)) were shown to be a function of the applied stress. By an increase of stress of 1.6 MPa, T(CIE) could be increased by 10 K.