Anionic polymerization of styrene and butadiene initiated by n-butyllithium in ethylbenzene: Determination of the propagation rate constants using Raman spectroscopy and gel permeation chromatography

The rate of monomer loss during the n-butyllithium-initiated anionic polymerization of styrene in ethylbenzene has been measured using Raman spectroscopy. Gel permeation chromatography measurements on the reaction products have been used as an indirect method of obtaining the concentrations of the propagating species involved in the reaction. The rate of propagation for styrene polymerization has been determined in the temperature range 25 to 70 degrees C, and for live-end concentrations between 9.1 x 10(-5) and 6.7 x 10(-3) mol l(-1). The order of the propagation reaction with respect to live-end concentration was found to be 0.53. The measured apparent rate constant for the propagation reaction was (1.8 +/- 0.4) x 10(-1)mol(-0.5) l(0.5) s(-1) at 70 degrees C, and the apparent activation energy was 75 +/- 8 kJ mol(-1) The rate of propagation for 1,3-butadiene has also been determined in the temperature range 39 to 72.3 degrees C, and for live- end concentrations between 5.6 x 10(-4) and 1.9 x 10(-3)moll(-1). The apparent rate constant for the propagation reaction was (7 +/- 2) x 10(-2) mol(-0.5) l(0.5) s(-1) at 70 degrees C and the activation energy was 72 +/- 14 kJ mol(-1) assuming 0.5 order with respect to live-end concentration. The activation energy found, assuming an order of reaction of 0.25, was 70 +/- 17 kJ mol(-1). The kinetic data for the butadiene system are less reliable than for styrene as can be seen from the limits of error quoted. The reaction has been confirmed to be internally first order with respect to monomer concentration to high conversions for both monomers examined. Crown copyright (C) 1996 Published by Elsevier Science Ltd.