Polystyrene Molecules Research Articles

THE DIFFUSION OF POLYSTYRENE IN DIFFERENT SOLVENTS

The variation of the diffusion coefficient of polystyrene with molecular weight in bromobenzene, toluene, and methyl ethyl ketone, obtained with a modified Northrop cell, obeyed the relation 1/D = AMε where A and ε are empirical constants. The decrease in the exponent ε with increasing molecular weight agrees qualitatively with the predictions of Debye and Bueche. Both the exponent and the ratio of the diffusion coefficients of a low to high molecular weight sample increased in better solvents, indicating that in such solvents the polystyrene molecules are elongated. Using this ratio as a criterion of solvent power, there is good agreement with the results of swelling and precipitation studies. The decrease in the diffusion coefficient – solvent viscosity product for a low and a high molecular weight polymer in good solvents suggests an increase in the degree of solvation of the polymer. The variation of this product with solvent composition in solvent mixtures indicates the existence of selective solvation by the good solvent. The activation energies of diffusion were of the order of 3 kcal. for both high and low molecular weight polymers in good and poor solvents. This supports Eyring's theory of segment flow for polymer diffusion.

Mechanism of vinyl polymerizations. VIII.1 Introduction of foreign end groups

AbstractResults are reported of experiments designed to delineate more clearly the action of retarders and chain transfer agents and to place different labeled end groups at either end of polystyrene molecules.

The formation and structure of polymers of the insoluble cross-linked type

Staudinger, in a series of papers (1934,1935,1936) describes the formation of an insoluble polymer of styrene by the addition to the styrene, before polymerization, of small quantities of p -divinyl-benzene. This insolubility he explains by suggesting the formation of cross-linkages of divinyl-benzene between the long thread-like molecules of polystyrene to give three-dimensional macromolecules of exceedingly high molecular weight. By using increasing proportions of divinyl-benzene Staudinger obtained a series of polymers which varied from polystyrenes soluble in benzene through polymers of high swelling capacity to completely insoluble pro­ducts. He considers that the cross-linkages of divinyl-benzene prevent the dispersion of the substance throughout the solvent, while it does not prevent the solvation of the long polystyrene chains. Thus, when few such cross-linkages are present, i. e. when the concentration of divinyl-benzene is low, the polymer will have a great tendency to go into solution through the solvation of the polystyrene chains, but will be prevented from becoming completely dispersed by the presence of the cross-linkages. The product will therefore have a high swelling capacity in those solvents in which the straight chain polystyrenes are soluble. This swelling capacity will decrease as the concentration of divinyl-benzene increases until com­pletely insoluble polymers are obtained.