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 experimentally observed in the phase separation process of polystyrene derivatives–poly(vinyl methyl ether) (PS-PVME) mixtures. The phase separation was controlled by manipulating, with ultraviolet light, the reversible changes in polymer segmental volumes associated with the trans-cis conformational transitions of stilbene molecules chemically attached on the PS chains. It was found that when the rate of the forward trans→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 α less than 0.1, whereas α is in between $\frac{1}{4}$ and $\frac{1}{3}$ when the reaction is turned off.