Spectroscopic studies of the compatibility of small molecules in polymers

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Abstract
A spectroscopic technique has been developed to study the compatibility and stability of small molecules in polymers. The technique was applied to investigate the compatibility of an electron-acceptor molecule, n-butyl 9-dicyanomethylene fluorene-4-carboxylate (BDFC), 1, in six different polymers. The electronic absorption of the small molecule 1 in polymer films as a function of concentration and temperature was examined. The deviation in the absorption of 1 from the molecular absorption properties was taken to indicate the degree of incompatibility (phase separation). The small molecule 1 was found to be most compatible with halogenated and electron-donating polymers.In general, our results indicated the existence of very strong intermolecular interaction between the small molecules and weaker small molecule – polymer interaction, which lead to the small molecule aggregation, i.e., incompatibility. The extent of aggregation of 1 in various polymers varied with the concentration of 1, the speed of drying the film, and the post-casting heat treatment. Aggregation of 1 in polycarbonate was drastically suppressed by incorporating a donor molecule into the matrix.

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