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Using the method of small-angle x-ray scattering (SAXS), the time-dependent structural changes in some linear-segmented urethanes have been investigated. The results directly support the time- and temprature-dependent morphological model proposed earlier by one of the authors. Specifically, upon heating of many linear urethanes, the degree of domain structure is decreased. Upon quenching to ambient temperature, there is a significant period of time required to reestablish the domain structure which, in turn, strongly influences the time-dependent mechanical behavior.

Epoxy network systems based on DOEBA (bisphenol-A-diglycidyl ether) and NMA (nadic methyl anhydride) systems modified with the low molecular weight CTBN (carboxyl-terminated butudieneacrylonitrile copolymer) rubbers were prepared and studied. It was found that below the glass transition of the epoxy matrix these materials displayed time-dependent changes in their mechanical properties; specifically, the strain to break as well as the rate of stress relaxation were observed to decrease in a nearlinear behavior with the logarithm of time at sub-Tg annealing. Calorimetric methods clearly showed a simultaneous decrease in enthalpy with time that behaved in a similar fashion as the time-dependent mechanical properties. All the calorimetric and mechanical data are qualitatively related. The importance of this phenomena is considered in view of the widespread use of epoxys. Similar behavior is expected for other network glasses thermally quenched into a non equilibrium state.

The interfacial tensions of immiscible binary blends of poly(dimethyl siloxane) (PDMS) and polybutadiene (PBD) have been determined as a function of molecular weight and temperature. The technique employed for these measurements takes advantage of recent advances in the determination and analysis of pendant fluid drop profiles. The experimental data are compared to the predictions of square gradient theories and theories based on the diffusion equation approach as developed by Helfand and co‐workers. Qualitative agreement is obtained with both types of theory when the Flory‐Huggins interaction parameter is taken to be comprised of two terms: a temperature independent term of entropic origin; and an enthalpic term that is inversely dependent upon the temperature.

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