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

Experimental values of second‐order transition temperatures T_m 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), T_m is 82°C, independent of composition, while the difference Δβ in cubical expansion coefficient above and below T_m is directly proportional to the volume fraction of polystyrene in the mixture. Unplasticized saran behaves similarly in that T_m is constant while Δβ decreases linearly with increasing crystallinity. For molecular dispersions of incompatible materials both T_m and Δβ are functions of composition. It is shown that for most high polymers T_m increases with increasing intermolecular force constants, while the product of T_m and cubical coefficient of expansion above T_m is roughly constant (0.1 to 0.2).