Dilute solution properties and molecular characterization of polyvinyl chloride

Abstract

Dilute solution properties of twenty-five PVC fractions prepared from commercial and experimental bulk-polymerized PVC samples have been investigated by means of light-scattering, viscometry and exclusion-chromato-graphy. The following Mark-Houwink-Sakadura relationships: [ η ]THF25ºC = 1.63 10-2 Mw0.760 x 1.017 c.g.s.[ η ]cyclohexanone25ºC= 2.57 10-2Mw0.725x 1.02 c.g.s. have been found to be valid in a range of Mw-values between 6400 and 650000. The validity of various extrapolation procedures, proposed in order to calculate unperturbed dimensions and polymer-solvent interaction parameters from the empirical viscosity-molecular weight relationship, has been examined. The Kurata-Stockmayer method applied to the measurements in tetrahydrofuran yields a Ke-value equal to 0.14 c.g.s. The polymer-solvent interaction parameter derived by the same method is not in agreement with the one deduced from second virial coefficient measurements. Molecular weight distributions determined in commercial PVC samples can be adequately represented, in a first approximation, by the usual exponential distribution function, first proposed by Schulz. The chromatographic determination of MWD and its effect on the viscosity-molecular weight relationship are discussed. Finally, the possible occurrence of long chain branching in PVC has been investigated by means of an experimental study of the structure and properties of various polyethylene samples obtained by reduction with LiAlH4of commercial PVC polymers. The melting temperatures and the intrinsic viscosity -molecular weight relationship for the polyethylene samples, so obtained, were found to be identical with those of High Density Polyethylene. It is concluded that most PVC polymers contain only very few long branches, if any. © 1971, Walter de Gruyter. All rights reserved.