Elastomeric networks were prepared from ethylene‐propylene‐diene (DPDM) terpolymers containing 5‐ethylidene‐2‐norbornene as the diene monomer incorporated to facilitate crosslinking. Such materials, although highly elastomeric, show some crystallinity over much of the compositional range and thus an understanding of their mechanical properties requires characterization of this crystallinity in both the stretched and unstretched states. The properties and techniques used in the present investigation for this purpose were differential scanning calorimetry, stress‐strain isotherms (at various extension rates), stress‐temperature coefficients, birefringence and stress‐optical coefficients, polarized light microscopy, small‐angle light scattering, and wide‐angle x‐ray scattering. Correlations of the various types of results obtained are used to elucidate the dependence of EPDM network crystallization on composition, strain, and temperature. It was found to be particularly important to use a wide variety of techniques to provide a reliable characterization of the poorly developed crystallinity present in typical EPDM elastomers.

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Hydroxyl-terminated poly(diethylene glycol terephthalate) chains having number-average molecular weights of 7200 were end-linked into noncrystallizable trifunctional networks using an aromatic triisocyanate. The networks thus obtained were studied with regard to their stress-strain isotherms at 62, 70, and 88 °C. For elongation ratios up to 400% none of the isotherms displayed an increase or upturn in the reduced forces [/*], indicating that the polymer does not crystallize under stress, probably due to very unfavorable kinetic conditions. Force-temperature measurements at constant length and pressure are also reported for these networks. The ratio of the energy contribution to the total tension, /"//, calculated from these measurements and the thermal expansion coefficient were used to calculate the temperature coefficient of the mean-square end-to-end distance. It was found that d In (r2)0/dT = (1.01 ± 0.14) X 10~3 K™1. A similar value was obtained for this coefficient from thermoelastic measurements carried out on swollen networks. The analysis of the temperature coefficient of poly(diethylene glycol terephthalate) in terms of the rotational isomeric state model confirms the results obtained from NMR studies, according to which the gauche states about CH2-CH2 bonds in the polymer chain have an energy significantly lower than these states about similar bonds in poly(oxyethylene).

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