EFFECT OF THE SOLVENT UPON THE DIFFUSION-COEFFICIENT OF POLYDISPERSE POLYSTYRENE AND STYRENE-ACRYLONITRILE COPOLYMER IN DILUTE-SOLUTION

In the reported experiments, a laser homodyne spectrometer was used to obtain translational diffusion coefficients for dilute polystyrene and styrene-acrylontirile copolymer solutions at room temperature. Data were obtained in the concentration range from 0. 01 to 2. 0 g polymer per 100 cm**3 solution for polystyrene in benzene and in decalin; and for copolymer in dimethyl formamide, in methyl ethyl ketone, and in benzene. For each of the systems investigated the concentration dependence of the diffusion coefficient was linear over the concentration range studied, and was expressed as D(c) equals D//0(1 plus k//Dc). Values of D//0 could be explained with a modified Kirkwood-Riseman expression. Values of the parameter k//D obtained from the slopes could be interpreted using the two-parameter theory approach as suggested by Vrentas and Duda. The value of k//D is positive for high-molecular-weight polymers. For a particular polymer, the molecular weight at which k//D changes sign is greater for poor solvents than for good solvents. observed values of D//0 were1 multiplied by 10** minus **7 to 7 multiplied by 10** minus **7cm**2/sec.