SOFT-MODE SUPPRESSION IN THE PHASE-SEPARATION OF BINARY POLYMER MIXTURES DRIVEN BY A REVERSIBLE CHEMICAL-REACTION

Soft-mode suppression driven by a reversible photoisomerization was ex perimentally observed in the phase separation process of polystyrene d erivatives-poly(vinyl methyl ether) (PS-PVME) mixtures. The phase sepa ration was controlled by manipulating, with ultraviolet light, the rev ersible changes in polymer segmental volumes associated with the trans -cis conformational transitions of stilbene molecules chemically attac hed on the PS chains. It was found that when the rate of the forward t rans-->cis reaction is comparable to its backward cis-->trans process. the phase separation becomes extremely slow and follows the Lifshitz- Slyosov-Wagner law t(alpha) with alpha less than 0.1, whereas alpha is in between 1/4 and 1/3 when the reaction is turned off.