Thermal Expansion and Second-Order Transition Effects in High Polymers: Part I. Experimental Results

Abstract

Experimental values of second-order transition temperatures Tm and of cubical expansion coefficients below and above this temperature are presented for several new materials, notably saran. The thermal expansion behavior of two-component systems of incompatible materials (polystyrene plus polyolefins) has been studied. For relatively coarse dispersions (1000A), Tm is 82°C, independent of composition, while the difference Δβ in cubical expansion coefficient above and below Tm is directly proportional to the volume fraction of polystyrene in the mixture. Unplasticized saran behaves similarly in that Tm is constant while Δβ decreases linearly with increasing crystallinity. For molecular dispersions of incompatible materials both Tm and Δβ are functions of composition. It is shown that for most high polymers Tm increases with increasing intermolecular force constants, while the product of Tm and cubical coefficient of expansion above Tm is roughly constant (0.1 to 0.2).