Comparison of solution and gel permeation fractionation of a cis‐1,4‐polybutadicne

Abstract

A sample of cis‐1,4‐polybutadiene was fractionated into 10 fractions by a coacervation method and the fractions evaluated by a combination of light scattering, osmometry, and viscosity. Calculation of the number‐ and weight‐average molecular weights from the fractionation data gave good agreement with measurements on the bulk polymer. Reconstitution of the polymer from the fractions also resulted in molecular weight values in agreement with those of the original polymer. Fractionation of the same polymer was carried out by using the Waters gel permeation chromatograph. Comparison of the data from the gel permeation fractionation with that of the coacervation fractionation, treated by the method of Beall, reveals marked differences. The gel permeation fractionation gives an overall wider distribution with lower number‐ and weight‐average molecular weights. The difference may be partially explained by the diffusion of low molecular weight material through the osmotic membranes resulting in high values of M̄_n. Isopiestic measurements tend to support lower values of M̄_n.