Glass-transition Temperature and Thermal Expansion Coefficient of a Two-Phase System of Polymers

Publisher Website
Google Scholar
Abstract
The abnormal increase of glass-transition temperature (T g) and the deviation of thermal expansion coefficient from the simple additivity relationship in a two separate phase system having different Tg, s were explained by the thermal stress originating from the difference of the thermal expansion coefficients of the two component polymers. Among the two T g, s of the blend system, the higher Tg was increased and the lower Tg was decreased compared with the original T g s of the component polymers in some cases. The spherical shell model composed of three layers was adopted to interpret such phenomena of the blend system. These three layers were numbered 0, 1, and 2 from the outer layer. The component polymer of the layer 0 was assumed to be the same as in the layer 2. In this model, vs, which is defined as the volume ratio of the sphere 2 to the sphere 1, represents the mixing state of the two component polymers. The thermal expansion coefficients of the whole system and the layers 0, 1, and 2 were calculated on the basis of this model. The agreement between the calculated and the observed values was rather good for the blend systems of polystyrene(PS)/polybutadiene (PBD), PS/styrene-butadiene rubber (SBR), polymethylmethacrylate(PMMA)/SBR and styrene-acrylonitrile copolymer/PBD. The blend system of PS/PMMA did not follow the above prediction. It was pointed out that in such a case the molecular interaction between two component polymers should be taken into account.