KINETIC MATRIX EFFECT ON PHOTOCHROMIC REACTIONS OF SPIROBENZOPYRAN DISPERSED IN OR COVALENTLY BOUND TO POLY(ALKYL METHACRYLATE) MATRICES

Spirobenzopyran (SP) was dispersed (DP) in or covalently bound (CB) to poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly (isopropyl methacrylate) (PiPMA) matrices. The extent of coloration due to formation of a merocyanine was smaller in CB than in DP matrices on irradiation of a single pulse of a Nd: YAG laser (355nm). Photochemical isomerization from a merocyanine to a SP obeyed the first-order kinetics above Tg of the matrix polymer, but not below Tg. The isomerization below Tg was analyzed on the basis of the kinetic matrix effect, by assuming a temperature-independent fast isomerization and a temperature-dependent slow isomerization at lower T than 240K, but only a temperature-dependent isomerization at higher T than 240K. The matrix response function time constant, α, for the fast isomerization was larger in CB than in DP matrices. Arrhenius plots of α for the slow isomerization showed discontinuities at characteristic temperatures of matrix polymers.