Photochromic behavior of copolymers of indolinospirobenzopyrane methacrylic derivatives

Abstract

AbstractThree photochromic 3,3‐dimethyl‐6′‐nitroindolinospirobenzopyran methacrylic derivatives have been synthesized, namely, 1‐methyl 8′‐methacryloxymethyl (A), 1‐(β‐methacrylamidoethyl) (B), and 1‐(β‐methacryloxyethyl) (C). They have been copolymerized with methyl, isobutyl, and n‐propyl methacrylates. The photochromic behavior of these copolymers in the solid state has been compared to that of the homologous isobutyric compounds dissolved in corresponding polymeric matrices. The kinetics of decoloration were resolved in three simultaneous first‐order reactions with rate constants k1, k2, and k3. The influence of the polarity of the polymeric matrix and of the photochrome incorporation has been examined. The rates of decoloration of the copolymers with isobutyl and n‐propyl methacrylate are very sensitive to the glass transition temperature Tg; the activation energy of decoloration increases markedly above Tg, from 19.8 to 36.5 kcal; below Tg the entropy of activation is strongly negative (around ‐20 e.u.), above Tg strongly positive. These effects are interpreted on the basis of an increasing chain segment mobility above Tg.