The extent to which the intramolecular heterophotodimerization of the photochromic molecule 9-(hydroxymethyl)-10-[(naphthylmethoxy)methyl]anthracene (HNMA), incorporated into a poly-(methyl methacrylate) (PMMA) matrix, is induced by irradiation with linearly polarized light was investigated. The degree of photodimerization was evaluated by using the polarization-induced efficiency parameter, 7, which is defined as the normalized difference between the two components of dichroic absorbance. It was found that 7 is affected by both the @-relaxation process and the glass transition temperature, Tg (T, = 103 "C) of the PMMA matrix. As irradiation time increases, 7 increases and reaches a limiting value, qmar, of ca. 6% at temperatures of around 40 "C. These results indicate that, by utilizing the selective induction of the intramolecular heterophotodimerization of HNMA, which occurs upon excitation with polarized light, it is possible to generate and control the spatial distribution of the refractive index of glassy polymer films, thereby making them potentially useful as optoelectronic materials for wave guiding or light modulation.
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. Photocross-links were carried out by utilizing the intermolecular photodimerization reaction between anthracene groups that were chemically attached on polystyrene chains (Macromolecules 1989(Macromolecules ,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 d's of these irradiated blends shift toward the higher temperature side as the delay time of irradiation increases. Though only PSA chains were cross-linked, these ordered structures are thermally quite stable.
Selectivity of the intramolecular photodimerization of a bichromophoric molecule, 9-(hydroxymethyl)-10-[(naphthylmethoxy)methyllanthracene (HNMA), in the glassy state of poly(methy1 methacrylate) (PMMA) was examined upon irradiation with linearly polarized light. Effects of temperature, dopant (HNMA) concentration, and uniaxial elongation of polymer matrix on the induction efficiency (Macromolecules 1990,23, 3002) of HNMA were investigated. It was found that upon increasing dopant concentration, the maximum induction efficiency shifts toward the lower temperature side. The same behavior was also observed as the elongational ratio of the PMMA matrix increases. Uniaxial elongation also results in an increase of 7. On the other hand, the induction efficiency grows exponentially with irradiation time and ia characterized by the growth rate K. The temperature dependence of K indicates that the polarization selectivity of HNMA in PMMA matrix is determined by both orientational relaxationand the conformational transitions of the molecule. Finally, the spatial distribution of reacted HNMA in PMMA induced by polarized light was found to be quite stable. In PMMA, 7 is reduced to half of its initial value after 10 months at room temperature.
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