THERMAL REVERSIBILITY IN LIQUID LIQUID-PHASE TRANSITION IN POLY(VINYL ETHYLENE-CO-1,4-BUTADIENE) POLYISOPRENE BLENDS

For rubber blends of poly(vinyl ethylene-co-1, 4-butadiene) with polyisoprene, reversible changes between phase dissolution and separation in the lower critical solution temperature (LCST) phase behavior were confirmed by differential scanning calorimetry. After the first annealing carried out to induce phase separation at a temperature above LCST, phase dissolution could be observed at the second annealing at a temperature T<LCST, based on the liquid-liquid phase equilibrium. Observing phase transition from the double to the single Tg states, the phase dissolution time was found to be 6∼379 min. This dissolution time depends on both blend composition and annealing temperature. The apparent-activation energies of the phase dissolution were calculated to be −3.6∼17.34 kcal mol−1. The negative values of apparent-activation energies for the phase dissolution could be explained based on the equation of state. © 1990 The Society of Polymer Science, Japan.