High-Strength Triple Shape Memory Elastomers from Radiation-Vulcanized Polyolefin Elastomer/Polypropylene Blends

High-strength and high-temperature triple shape memory elastomers from multiphase polyolefin elastomer (POE)/polypropylene (PP) blends are prepared via radiation-induced vulcanization. Irradiation generates cross-linking mainly in the amorphous sequences of POE chains, long chain branches in the amorphous regions of PP crystals, and grafting between PP and POE chains at the interface of the POE and PP phases. The discoid-like PP phase with an average size of 1.6 x 11 mu m(2), dispersed in the POE matrix, is aligned parallel to the plane of the recompressed films. The PP lamellar crystals is partially orientated, and the PP lamellar crystals with (040)(alpha) and (110)(alpha) planes are arranged parallel and perpendicular to the surface of the highly cross-linked films, respectively. The integration of heterogeneous macromolecular structure, partially orientated crystals, and separated multiphase morphology contributes to excellent triple shape memory effects and high tensile strength up to 38 MPa. Consequently, two temporary shapes with fixity ratios of 82 and 97% are programmed by the reversible aggregation and solidification of the segregated PP lamellar crystals and POE bundle-like crystals. Under thermal triggering at the switching temperatures of 90 and 180 degrees C, the entropy-driven elasticity of the discrete PP and POE switching segments provides a good shape recovery of 88 and 94% to the memorized complex permanent shape. These results indicate that designing and tailoring the unconventional macromolecular architecture and condensed-state structure provide a novel strategy for developing low cost, high performance, and flexible intelligent polyolefins.