| The miscibility of a series of hydrogen bonded polymer blends, comprised of poly(n-hexyl methacrylate) (PHMA) and a series of poly(styrene- co-vinyl phenol) (STVPh) copolymers, were studied by differential scanning calorimetry (DSC). Copolymers containing 7 mole% vinyl phenol units (STVPh7), 10% (STVPh10), and 13% (STVPh13) were found to be miscible with PHMA. The thermally induced phase separation of the 50/50 STVPh/PHMA blend was chosen for detailed study because the phase separation temperature was located well below the thermal degradation temperature but above the glass transition of the blend. Additionally, the ability to freeze the morphology of the phase separated state by quenching made this blend an attractive candidate for our investigation.; The thermally induced phase separation was studied by temperature-modulated differential scanning calorimetry (TMDSC), which can resolve close transitions due to its high sensitivity and resolution. A phase diagram was constructed from the TMDSC data. The kinetics of phase separation were studied by determining the phase compositions from the glass transition temperatures of quenched samples after phase separation. After the 50/50 STVPh7/PHMA blend was allowed to undergo phase separation at 140°C, the composition of the STVPh7-rich phase appeared to have reached its final value after 60 min, but the composition of PHMA-rich phase was still short of its limiting value. The phase compositions changed smoothly with time and no apparent discontinuity was found in the curve even though the STVPh7-rich phase must have crossed the boundary between the unstable and metastable regions.; The phase separated samples were annealed at temperatures below the phase boundary to observe the return to the homogeneous state. A maximum rate of re-mixing was found at around 110°C for the 50/50 STVPh7/PHMA blend. When the phase separated sample was conditioned isothermally at 110°C the rehomogenization process was accompanied by a decrease in the size of the STVPh7-rich domains by diffusion into the matrix. |
