Enthalpy relaxations and concentration fluctuations in blends of polystyrene and poly(oxy-2,6-dimethyl-1,4-phenylene)

Abstract

A series of enthalpy relaxation measurements were carried out for the pure polymers polystyrene (PS) and poly(oxy-2,6-dimethy¡-1,4-phenylene) (PPE) and for homogeneous blends thereof. The data were analyzed using Moynihan's four-parameter approach.4 For the pure components the best fit parameter values for the simple cooling/heating experiments differ somewhat from those for the annealing experiments at least partly due to thermal lag. The amount of enthalpy relaxation during annealing of the blends turned out to be considerably lower than for the corresponding homopolymers. Moreover, the annealing experiments on the blends could not be fit satisfactorily with the Moynihan model. The first observation agrees with a similar result found by Cowie and Ferguson17 for blends of PS and poly (vinyl methyl ether). Since this effect is not present for a number of polymer blends involving polymers with comparable glass transition temperatures, it seems to be related to the large difference in glass transition temperatures of the blend components. The presence of concentration fluctuations, with a corresponding range of T¡ values, is the most obvious explanation for both observations.

Enthalpy relaxation studies in polymethyl methacrylate networks with different crosslinking degrees

“…In fact, DSC has proved to be a very useful technique to characterize the heterogeneity and the increase of the temperature interval where the glass transition takes place for multi-component polymeric systems (see, for example, [37,38] and references cited therein). Moreover, it has been found that the kinetics of the structural relaxation process, closely related to the glass transition, is significantly different in multi-component systems, when compared to the process of the pure components [28,39,40]. The influence of the crosslink density on the kinetics of structural relaxation will also be investigated for the PMMA networks.…”

Glass‐formation kinetics of miscible blends of atactic polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)

“…It is uncommon for a pair of high molecular weight polymers to form completely miscible mixtures, but blends of these two components display miscibility throughout the entire composition range. Mixtures of a‐PS and PPO have been investigated with regard to component interactions and miscibility,1–7 glass‐transition behavior,8–10 thermodynamic characteristics,11–14 barrier properties,15–17 mechanical properties,18–22 orientation and relaxation behaviors studied with rheo‐optical techniques,23–26 dielectric and dynamic mechanical responses,8, 18, 27–29 rheology,30, 31 physical aging,32–39 and free‐volume properties determined with positron annihilation lifetime spectroscopy 38, 40…”

Physical Aging of Polymer Blends

“…For PS/PPO blends, negative deviations from simple additivity have been observed, for small undercoolings which seem to disappear upon aging at temperatures deep in the glassy state (Robertson and Wilkes 2000). To verify whether this behavior was to be attributed to concentration fluctuations and the breadth of the glass transition as suggested by Oudhuis and ten Brinke (1992), Robertson and Wilkes (2000) scaled the volume relaxation rates by the onset temperature, T onset and T g , and found similar trends. Therefore, the authors concluded that the volume data provided no evidence of concentration fluctuations being responsible for the trends in volume relaxation rate.…”

“…As shown by data in Table 13.4, the degree of intermolecular coupling of the PVME segments substantially increased in the blend (average n ¼ 0.41 for PVME vs. average n ¼ 0.60 for the blend). The work of Oudhuis and ten Brinke (1992) on the aging of blends of PS with poly(2,6-dimethyl-1,4-phenylene oxide), PPO, provides an interesting comparison with the PS/PVME system. In PS/PPO blends, both components are relatively rigid, although there is still about 100 C difference between the T g values.…”