Various amounts of silica nanoparticles were chemically incorporated into amorphous polyurethanes (PU) of two different molecular weights by sol-gel reactions, and the effects were studied in terms of mechanical, dynamic mechanical, dual, and triple shape memory effects (DSME and TSME) of the nanocomposite films. It was found that the silica particles act as multifunctional cross-links as well as reinforcing fillers and significantly augmented the glassy and rubbery state moduli, yield strength, break strength, glass transition temperature, and dual shape memory properties. A cohesive bilayer of the two films fabricated from an interpenetrating polymer network (IPN) exhibited synergistic mechanical properties in the glassy and rubbery states along with two undisturbed glass transitions by which an intermediate plateau region and TSME were demonstrated.

No abstract

Polyurethane (PU)-silica nanocomposites were synthesized by sol-gel reactions between the surface silanol groups of fumed silica and 3-aminopropyltriethoxysilane (APTES) terminated PU with a broad range of silica contents (1-5%) with two different molecular weights of PU. It was found that the silica particles that were incorporated into the polymer chains were well dispersed in the PU matrix and acted as multifunctional cross-links and reinforcing fillers; in addition, the silica particles augmented the initial and rubbery moduli, yield, and break strengths, as well as the glass transition temperature. Moreover, 98-99% shape fixity and shape recovery with minimum cyclic hysteresis were obtained with only 1% silica particle loading.