STRUCTURE OF POLYMER BLENDS PHOTO-CROSS-LINKED DURING THE SPINODAL DECOMPOSITION PROCESS

Anthracene-labeled polystyrene/poly(2-chlorostyrene) blends (PSA/P2CS) with the composition 40/60 were photo-cross-linked during the time evolution of the spinodal-decomposition process. Photo-cross-links were carried out by utilizing the intermolecular photodimerization reaction between anthracene groups that were chemically attached on polystyrene chains (Macromolecules 1989, 22, 2107). The structure and property of these photo-cross-linked blends were examined by means of optical microscopy and dielectric relaxation. It was found that, upon irradiation with a XeF excimer laser, the ordered structures resulting from a temperature-jump (T-jump) from the one phase into the spinodal region were efficiently frozen. For a constant duration time of irradiation (5 min), the sizes of these ordered structures become larger as the blend was photo-cross-linked at a later time. Furthermore, the ordered structures revealed in these irradiated blends are different from those experiencing the same T-jump condition without irradiation. The corresponding maxima of the dielectric tan delta's of these irradiated blends shift toward the higher temperature side as the delay time of irradiation increases. Though only PSA chains cross-linked, these ordered structures are thermally quite stable.