Fluorescence study of interpenetrating network morphology of polymer films

Abstract

Fluorescence experiments were carried out on polymer films composed of poly (vinyl acetate) (PVAc, 91.7 mol%) and poly (2-methylhexyl methacrylate) (PEHMA, 8.3 mol%) (all the PEHMA present as a graft copolymer), which 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 \(\bar d\)=1.3. This result can be explained by the Exponential Series Method (ESM) in terms of a crossover phenomenon in restricted geometries, if the PEHMA is present in the film in the form of interconnected, long, thein (ca. 25 A diameter) cylinders. Supporting this idea is our finding that swelling agents for PHEMA such as hexadecane are also taken up by the film from pentane solution. Experiments on these materials give \(\bar d\)values that increase with increasing hexadecane until \(\bar d\)becomes equal to 3.0. These final results support the idea that PEHMA forms an interpenetrating network in glassy PVAc film.