Phase separation of anthracene-labeled polystyrene/poly(vinyl methyl ether) (PSA/PVME)
blends was induced by photo-cross-linking the PSA chains with linearly polarized light in the one-phase
region of the blend. The cross-linking reaction was performed by taking advantage of the polarization-selective photodimerization of anthracene labeled on the PSA chains. Under this particular irradiation
condition, the spatial symmetry of concentration fluctuations was broken, resulting in anisotropic phase
separation directed by the exciting polarization. By comparison of these experimental data with those
obtained by using unpolarized light under the same conditions, it was found that the morphology induced
by linearly polarized light reflects the interference between instabilities propagating with different rates
along different directions in the reacting blends.
Symmetry breaking of concentration fluctuations was found in a binary polymer mixture with one component photo-cross-linked by linearly polarized light. As the reaction proceeds, the mixture undergoes phase separation, exhibiting lamellar morphologies with the direction closely perpendicular to the polarization (E) of the exciting light. It was also found that the phase separation is suppressed in the parallel direction and its kinetics strongly depends on the relative orientation with respect to the exciting polarization. Thus, these reacting mixtures provide a model system to study the directional phase separation driven by chemical reactions. ͓S1063-651X͑98͒51002-1͔PACS number͑s͒: 61.41.ϩe, 82.35.ϩt
Mixtures of polystyrene derivatives (PSCS) and poly(vinyl methyl ether) (PVME) were made photocrosslinkable by chemically labeling PSCS chains with photoreactive anthracene. Miscibility of these anthracene-labeled PSCS/PVME blends was examined by light scattering under several crosslinking conditions in the one-phase region via photodimerization of anthracenes. As the reaction proceeds, the coexistence curve of PSCS/PVME blends shifts toward the low temperature side. By following the changes in concentration of anthracenes with irradiation time, it was found that the crosslinking reaction of PSCS chains in the blends does not follow the mean-field kinetics. However, it can be well expressed by the Kohlrausch-Williams-Watts (KWW) relaxation mechanism, indicating that the crosslinking reaction proceeds inhomogeneously in the blends. By scaling the reaction time with the average reaction rate obtained from the KWW equation modified for the reaction kinetics, all the crosslinking data obtained in the miscible region of the reacted blends fall on a single master curve. These experimental results suggest the universal behavior of the photocrosslinking kinetics obtained under the ''shallow quench'' conditions in the region far away from the coexistence curve of the reacting blends.
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