Branching in poly(butadiene‐co‐styrene). I. Branching determined by viscometry and ultracentrifugation

Abstract

AbstractA sample of poly(butadiene‐co‐styrene), SBR, was divided into twelve fractions by precipitation from a dilute benzene solution. The intrinsic viscosities [η] and weights of all the fractions were measured, and the sedimentation coefficients s0 were determined for the nine fractions of highest molecular weight. From the values of [η] and s0 the number of crosslinks per molecule m, was calculated for each fraction. The results indicated that only the four fractions of highest molecular weight contained crosslinked molecules. The number of crosslinks per weight‐average primary (prior to crosslinking) molecule for the entire sample, δ0, was obtained from the weights of the fractions and the values of m. By use of various theories, values of δ0 of 0.78, 0.56, and 0.38 were obtained. From the values obtained for [η] and s0 and the pycnometric partial specific volume of the polymer in benzene, the molecular weights M of the nine fractions of highest [η] were calculated. The molecular weights of the remaining fractions were calculated from the relation between M and [η] obtained by others. A molecular weight distribution curve was established and used to obtain δ0 ≤ 0.36.