Effects of molecular weight and interaction parameter on the glass transition temperature of polystyrene mixtures and its blends with polystyrene/poly (2,6-dimethyl- p-phenylene oxide)

The glass transition temperature ( T g ) of mixtures of polystyrene (PS) with different molecular weight and of blends of poly(2,6-dimethyl- p-phenylene oxide) (PPO) and polystyrene with different molecular weight (DMWPS) was studied by a DSC method. For the whole range of composition, the curves of T g vs composition obtained by experiment were compared with predictions from the Fox, Gordon-Taylor, Couchman and Lu-Weiss, equations. It was found that the experimental results were not in agreement with those from the Fox, Gordon-Taylor and Couchman equations for the binary mixtures of DMWPS, where the interaction parameter χ was approximately zero. However, for the blends PPO/DMWPS (χ < 0), with an increase of molecular weight of PS, it was shown that the experimental results fitted well with those obtained from the Couchman, Gordon-Taylor and Fox equations, respectively. Furthermore, the Gordon-Taylor equation was nearly identical to the Lu-Weiss equation when ¦χ¦ was not very large. Further, the dependence of the change of heat capacity associated with the glass transition ( ΔC p ) on the molecular weight of PS was investigated and an empirical equation was presented.