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PTFE specimens with a crystallinity of 42 % were uniaxially stretched at 473 K resulting in draw ratios between 1 and 4. The degree of molecular orientation was obtained by X-ray wide angle and birefringence measurements. The thermal expansion coefficients and the Young's moduli both parallel and perpendicular to the draw direction were measured in the temperature range from 100 to 400 K. The thermal expansion behaviour turned out to be dependent upon the molecular orientation in a sensitive manner and could be explained by a simple model of structure changes caused by the deformation processes.

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Heat capacities Cp of a polydiacetylene‐bis(toluene sulfonate) single crystal and its monomer have been measured in the temperature range from 3 to 300 K. The temperature dependence of Cp for both monomer and polymer crystals differs from that for monoatomic solids. By applying a chain lattice model for a polymer crystal, the temperature dependence of the heat capacity can be described assuming a phonon density of states given by bending and stretching modes of the polymer backbone. With a combination of one‐dimensional and three‐dimensional elastic continuum approximations, the heat capacity has been calculated and a good fit to the data has been obtained. A small peak in Cp was detected at 161 K for the monomer and at 198 K for the polymer. This may be ascribed to a lower‐temperature phase transition in the polydiacetylene crystals evidenced by previous x‐ray and spectroscopic measurements.

SummaryFractural length changes Ai/I of a polydiacetylene (toluene sulfonate) single crystal and its monomer have been measured along the crystallographic a-, b-, and c-direction in the temperature range 100 to 400 K. Small steps in the temperature dependence of All1 at 194 K for the polymer and 159 K for the monomer are assumed to be caused by a well known phase transition. From the volume coefficient of thermal expansion the bulk Grfineisenparameter 7b has been calculated. Temperature dependence as well as absolute values of Yb for the polymer crystal are found to be in accordance with current theories assuming that both interand intrachain vibrations strongly influence the thermoelastic behaviour of polymer crystals.