The specific volume of poly(tetrafluoroethylene) as a function of temperature (30°–372°C) and pressure (0–2000 kg/cm2)

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Experimental data on the specific volume of a 50% crystalline sample of poly(tetrafluorethylene) are presented and discussed. Data points were taken along 22 isotherms spaced 5 to 30°C apart (up to 372°C) in pressure increments of 100 kg/cm2 up to 2000 kg/cm2. In addition to the melting transition and the first-order solid–solid transition near room temperature, a previously reported second-order transition near 140°C at P = 0 is observed. This transition shifts to higher temperatures with increasing pressure by about 0.015°C per kg/cm2. The melt data are discussed in detail. They can be fitted to both the empirical Tait equation, with the usual exponential temperature dependence of the Tait parameter, and to the Simha-Somcynsky hole theory (with the reducing parameters V* = 0.424 cm3/g, T* = 7906°K, and P* = 7100 kg/cm2 = 6960 bars), thus providing a test for this theory at high reduced temperatures near T̃ = 0.08.