Polymer Diffusion in PBMA Latex Films Using a Polymerizable Benzophenone Derivative as an Energy Transfer Acceptor

ABSTRACT: Fluorescence resonance energy transfer (FRET) measurements were used to monitor polymer diffusion in poly(butyl methacrylate) latex films with a polymer molar mass of Mw 125 000 (Mw/Mn) 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 (1 mol %) as the acceptor. The data were analyzed in two distinct ways. Our traditional simplified approach involved calculating fm values for the quantum efficiencies of FRET (…ET). Apparent diffusion coefficients Dapp were calculated by making rather severe assumptions about fm. 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 ID 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 Ea) 33.5 ( 2.5 kcal/mol from Dapp and 38 ( 5 kcal/mol from 〈D〉. These values are very similar to the value of Ea) 39 kcal/mol from Dapp obtained in earlier experiments in which anthracene served as the acceptor chromophore