THEORETICAL AND EXPERIMENTAL 2ND-HARMONIC GENERATION STUDIES OF THE ROTATIONAL ELASTIC RESPONSE OF A DYE MOLECULE IN A RANDOM COPOLYMER OF STYRENE AND METHYL-METHACRYLATE

We report on second harmonic generation measurements of a polymer-impeded electric field induced rotation of the dye molecule Disperse Red 1 in a series of styrene-methyl methacrylate copolymers of varying composition. We show, by wasy of analysis of a generalized hypothetical binomial or multinomial distribution, that the dye molecules are not randomly distributed through the polymer and apparently associate more strongly with the styrene and methyl methacrylate homopolymer regions. Alternatively, this could be viewed as evidence of nonrandom distribution of the two monomers of the copolymer: We further suggest through molecular mechanics calculations that the polymer molecular motion associated with the electric field induced rotation of the dye involves torsional rotations of the polymer side groups and main chain. It also appears that the elastic response inherent to the probe molecule constitutes no more than 10-15% of the overall elastic response measured for the probe/polymer mixture.