STUDY ON SHAPE-MEMORY BEHAVIOR OF POLYETHER-BASED POLYURETHANES - II - INFLUENCE OF SOFT-SEGMENT MOLECULAR-WEIGHT

Polyurethanes (PUs) of a suitable molar ratio of monomers were found t o have shape-memory behavior. In this study, four series of PUs were s ynthesized by 4,4'-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD), and various molecular weights of poly( tetramethylene oxide)glyc ol (PTMO) to study the influence of the soft segment (PTMO) on the sha pe-memory behavior of PUs. The investigation on thermal and dynamic me chanical properties was performed using DSC and DMA; then, the morphol ogy of the PUs was directly observed by TEM. At the range of the indiv idual glass transition, a similar recovering behavior was found from t he deformed specimen that contained the same composition but different molecular weights of PTMO. However, the phase separation between the soft and the hard segments of the PUs would influence their shape-memo ry behavior. On the other hand, a large number of the dispersed phase of the PUs would delay the recovery rate of the deformed specimens usi ng a high molecular weight PTMO. (C) 1998 John Wiley & Sons, Inc. J Ap pl Polym Sci 69: 1575-1586, 1998.