Emulsion polymerization of isoprene. Estimation of the branching exponent with the help of a mathematical model

Abstract

This work investigates a batch and unseeded emulsion polymerization of isoprene at 10°C with n-dodecylmercaptan as chain transfer agent (CTA). The obtained polyisoprene (PI) was analyzed by size exclusion chromatography (SEC) with on-line viscometry. A global polymerization model was adjusted to the measurements of conversion, average particle size, and average molecular weights. The CTA concentration strongly affects the average molecular weights but has a negligible effect on conversion, average particle diameter, and average branching. Due to the combined effects of chain transfers to the polymer and to the CTA, the final molar mass distributions exhibited dispersity indexes higher than 10. The polymerization model predictions on the average degree of branching was combined with an ideal SEC model for adjusting the branching exponent of PI in tetrahydrofuran at 25°C that resulted e = 2.5. A sensitivity analysis showed that p20% errors in Mw induced variations in e lower than -10%. © 2009 Wiley Periodicals, Inc.