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Polystyrene (PS) was blended with shape memory polyurethanes (SMPU). Styrene blocks were grafted onto PU chains during SMPU synthesis to yield a modified SMPU with a higher affinity towards PS. Furthermore, blends containing a compatibilizer, poly (styrene-co-maleic anhydride) (SMA), were also prepared by melt mixing the components. The non-compatibilized blends display phase separated structures with PS rich and SMPU rich phases, which were less evident in blends prepared with either the modified SMPU or SMA compatibilizer. The elastic storage modulus of PS was less affected when blended with SMPU in samples containing modified SMPU with styrene grafts. The impact strength of the blends with higher contents of SMPU modified with styrene blocks (25 and 50 wt.%), after shape recovery, was higher than the impact strength of neat PS. The incorporation of shape memory polymers into a brittle polymer matrix is a potential strategy to improve the toughness by external stimuli.

The relationship between shape-memory behavior and structure was studied using three series of poly(ester-urethanes) with varying amounts of hard segment. The materials were designed to display a three-phase structure consisting of a disperse phase of crystallites and hard domains embedded in an amorphous matrix based on soft segment. Structure and thermal properties of the resultant materials were investigated using techniques such as modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). The results revealed morphological changes in the materials during a low temperature shape-memory cycle. To study shape recovery, a deformed specimen was evaluated on a heating stage mounted at the SAXS beamline. Furthermore, to study the effect of temperature during recovery, the specimens were subjected to different thermo-cycles. Under each set of conditions, the phase morphology and composition were investigated. Temporary shape was stored by the metastable structure formed during deformation. The recovery was triggered by the melting of crystallites and hydrogen bonding between hard domains. The recovery process was divided into three stages. Bulk incompatibility and entropic recovery determined the final polyurethane morphology.