Abstract
A series of degradable polymer networks containing poly(ω-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 Rr 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 (TCIE and TMIC ) were shown to be a function of the applied stress. By an increase,of stress of 1.6 MPa, TCIE could be increased by 10 K.
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