ENERGY-TRANSFER STUDIES ON POLYMER MEMBRANE FILMS - MATERIALS WITH VARIABLE APPARENT DIMENSIONALITY

Polymer films composed of poly(vinyl acetate) (PVAc, 91.7 mol%) and poly(2-ethylhexyl methacrylate) (PEHMA, 8.3 mol%) (all the PEHMA picient as a graft copolymer) were prepared by solvent casting. The PEHMA phase was labeled with a low concentration (0.7 mol%/PEHMA) of naphthalene groups. Exposure of the films to a pentane solution of 9-anthrylmethyl pivalate (AMP) transferred the AMP molecules exclusively to the PEHMA phase of the material. Direct energy transfer studies showed that the energy transfer rate was proportional to the AMP concentration, and that the process was characterized by an effective dimensionality d = 1.4. This result can be explained in terms of a crossover phenomenon if the PEHMA is present in the film in the form of interconnected long, thin (≈ 50 Å diameter) cylinders. Supporting this idea is our finding that swelling agents for PEHMA such as hexadecane are also taken up by the film from pentane solution. Experiments on these materials give d values that increase with increasing hexadecane until d becomes equal to 3.0. © 1990.