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-impe ded electric field induced rotation of the dye molecule Disperse Red 1 in a series of styrene-methyl methacrylate copolymers of varying comp osition. We show, by wasy of analysis of a generalized hypothetical bi nomial or multinomial distribution, that the dye molecules are not ran domly distributed through the polymer and apparently associate more st rongly with the styrene and methyl methacrylate homopolymer regions. A lternatively, this could be viewed as evidence of nonrandom distributi on of the two monomers of the copolymer: We further suggest through mo lecular mechanics calculations that the polymer molecular motion assoc iated with the electric field induced rotation of the dye involves tor sional rotations of the polymer side groups and main chain. It also ap pears that the elastic response inherent to the probe molecule constit utes no more than 10-15% of the overall elastic response measured for the probe/polymer mixture.