Polymer diffusion in PBMA latex films using a polymerizable benzophenone derivative as an energy transfer acceptor

Fluorescence resonance energy transfer (FRET) measurements were used to monitor polymer diffusion in poly(butyl methacrylate) latex films with a polymer molar mass of M-w approximate to 125 000 (M-w/M-n = 2.5). These experiments employed the nonfluorescent acceptor chromophore NBen, which allowed faster data acquisition at lower acceptor dye concentration (0.3, 0.5 mol %) than previous experiments with anthracene (I mol %) as the acceptor. The data were analyzed in two distinct ways. Our traditional simplified approach involved calculating f(m) values for the quantum efficiencies of FRET (Phi(ET)). Apparent diffusion coefficients D-app were calculated by making rather severe assumptions about f(m). In addition, we carried out mathematical simulations of diffusion which satisfied Fick's laws in a spherical geometry. The concentration profiles of donor and acceptor were introduced into equations that describe the rate for of energy transfer, and donor decay profiles were simulated I-D(s)(t). By comparing simulated and experimental decay profiles as a function of sample annealing time, optimum values of the mean diffusion coefficient (D) were obtained. A comparison of the two different methods of data analysis indicates that Dapp values are larger than (D) values by a factor of 2-4 but track the "true" diffusion coefficients rather well. From the temperature dependence of the diffusion coefficients, we found effective activation energies for diffusion of E-a = 33.5 2.5 kcal/mol from D-app and 38 +/- 5 kcal/mol from <D>. These values are very similar to the value of E-a = 39 kcal/mol from D-app obtained in earlier experiments in which anthracene served as the acceptor chromophore.