Analysis of a Styrene-Butadiene Graft Copolymer by Size Exclusion Chromatography. II. Determination of the Branching Exponent with the Help of a Polymerization Model

VEGA, J. R.; ESTENOZ, D. A.; OLIVA, H. M.; MEIRA, G. R.

International Journal of Polymer Analysis and Characterization.

Lugar: New Jersey; Año: 2001 vol. 6 p. 339 - 348

A styrene-butadiene graft copolymer is analyzed by size exclusion chromatography (SEC) with on-line viscometry with the aim of estimating the epsilon exponent that relates the two branching parameters through g´= g exp(epsilon). Three copolymer samples synthesized in a solution polymerization of styrene in the presence of polybutadiene were analyzed. Theoretical predictions on the branching characteristics were obtained with the help of a detailed polymerization model that is presented in the first part of this series. The epsilon exponent was adjusted by comparing the experimental variation of g´ along molecular weights with the expected theoretical function. For tetrahydrofuran solutions at 25 C, a value of epsilon = 2 was obtained. The resulting average number of trifunctional branching points per molecule are in accord with independent determinations by gravimetry, ozonolysis, and SEC.