Physical aging behavior of miscible blends containing atactic polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide)

The influence of blend composition on physical aging behavior was assessed for miscible blends of atactic polystyrene (a-PS) and poly(2,6-dimethyl- 1, 4-phenylene oxide) (PPO). At aging temperatures of 15 and 30 degrees C belo w the midpoint glass transition temperature (T-g), the a-PS/PPO blends exhi bited volume relaxation rates that were retarded compared to additivity bas ed upon the aging rates for pure a-PS and PPO. This negative deviation dimi nished with increased undercooling, and eventually the volume relaxation ra tes displayed a nearly linear trend with respect to composition at the grea test undercooling of 60 degrees C that was employed. The compositional natu re of unaged glassy density and secondary relaxation intensity, both influe nced by the presence of specific attractive interactions in the blend syste m, were likely causes for the variation of volume relaxation rate with comp osition and undercooling. For aging at 30 degrees C below T-g, the dependen ce of enthalpy relaxation rate on composition was similar to that observed for volume relaxation. Mechanical aging rates determined from time-aging ti me superposition of creep compliance data showed significantly less than ad ditive behavior for the blends aged at T-g - 30 degrees C, but unlike the v olume relaxation results, this trend persisted at the 60 degrees C undercoo ling. (C) 2000 Elsevier Science Ltd. All rights reserved.