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Thermoresponsive shape memory polymers based on polyurethane with soft segment consisting of poly (tetramethylene oxide) (PTMO) and hard segment arising from urethane reaction of tolylene diisocyanate with OH terminal of PTMO and 1,4 butane diol (BD) were synthesized by a two-step process. The molar ratios of the reactants were varied to get polymers of different softhard segment contents. These were characterized by DSC, IR, DMTA, XRD, SEM analyses, and mechanical properties. The shape memory behavior was evaluated by cyclic tensile tests. PTMO served as the switching segments whose crystalline melting was responsible for the switching behavior. As the hard segment-content increased, transition temperature (T trans ) diminished and so did the elongation and tensile strength of the polyurethane. Higher glassy/rubbery modulus ratio observed for higher hard segment-content polymer was conducive to better shape recovery properties. The influence of hard/soft segments on the thermal, mechanical, damping and shape memory properties of the copolymers are presented and correlated to their phase morphology, as investigated by FTIR and SEM.

The viscoelastic properties of blends based on nitrile rubber (NBR) and ethylene-vinyl acetate copolymer (EVA), a thermoplastic elastomer, are investigated in terms of storage modulus and loss tangent for different compositions. These small-strain dynamic mechanical properties have been evaluated using a Rheovibron Viscoelastometer covering a wide temperature range. Attempts have been made to fit the experimental results with computations based on mean field theories developed by Kerner. Predictions based on the discrete particle model (which assumes one of the components of the blend to be the matrix and the other dispersed as inclusions) are found to be satisfactory in the case of 30/70 NBR/EVA blend but not 70/30 and 50/50 blends. The packed grain model (which assumes neither of the components to be the matrix but approximates a co-continuous structure of the two) predictions do not agree with the experimental data on 50/50 blend for which a co-continuous morphology was revealed by SEM observations.

The viscoelastic properties of binary blends of nitrile rubber (NBR) and isotactic polypropylene (PP) of different compositions have been calculated with mean-field theories developed by Kerner. The phase morphology and geometry have been assumed, and experimental data for the component polymers over a wide temperature range have been used. Hashin's elastic-viscoelastic analogy principle is used in applying Kerner's theory of elastic systems for viscoelastic materials, namely, polymer blends. The two theoretical models used are the discrete particle model (which assumes one component as dispersed inclusions in the matrix of the other) and the polyaggregate model (in which no matrix phase but a cocontinuous structure of the two is postulated). A solution method for the coupled equations of the polyaggregate model, considering Poisson's ratio as a complex parameter, is deduced. The viscoelastic properties are determined in terms of the smallstrain dynamic storage modulus and loss tangent with a Rheovibron DDV viscoelastometer for the blends and the component polymers. Theoretical calculations are compared with the experimental small-strain dynamic mechanical properties of the blends and their morphological characterizations. Predictions are also compared with the experimental mechanical properties of compatibilized and dynamically cured 70/30 PP/NBR blends. The results computed with the discrete particle model with PP as the matrix compare well with the experimental results for 30/70, 70/30, and 50/50 PP/NBR blends. For 70/30 and 50/50 blends, these predictions are supported by scanning electron microscopy (SEM) investigations. However, for 30/70 blends, the predictions are not in agreement with SEM results, which reveal a cocontinuous blend of the two. Predictions of the discrete particle model are poor with NBR as the matrix for all three volume fractions. A closer agreement of the predicted results for a 70/30 PP/NBR blend and the properties of a 1% maleic anhydride modified PP or 3% phenolic-modified PP compatibilized 70/30 PP/NBR blend in the lower temperature zone has been observed. This may be explained by improved interfacial adhesion and stable phase morphology. A mixed-cure dynamically vulcanized system gave a better agreement with the predictions with PP as the matrix than the peroxide, sulfur, and unvulcanized systems.

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