Analysis of a Styrene—Butadiene Graft Copolymer by Size Exclusion Chromatography I. Computer Simulation Study for Estimating the Biases Induced by Branching Under Ideal Fractionation and Detection

Abstract

This theoretical work estimates the deviations in the molecular weights distribution (MWD), the degree of branching distribution (DBD), and the chemical composition distribution (CCD) due to branching when a (chromatographically complex) styrenebutadiene graft copolymer is analyzed by ideal size exclusion chromatography (SEC). The copolymer was isolated from a high-impact polystyrene. A novel polymerization model was developed that predicts the MWD, DBD, and CCD for the total copolymer and for each of its different branched topologies. Copolymer topologies are characterized by the number of trifunctional branching points per molecule. To simulate the molecular weight calibrations in SEC, the Zimm — Stockmayer equation was applied to each copolymer topology. Negligible deviations due to branching were found in the MWD and the DBD with respect to the theoretical predictions provided by the polymerization model. In contrast, errors in the CCD are intolerably large and consequently the CCD cannot be estimated by SEC.