Polymerization of 1,3-Butadiene Initiated by Neodymium Versatate/Diisobutylaluminium Hydride/Ethylaluminium Sesquichloride: Kinetics and Conclusions About the Reaction Mechanism

Abstract

The kinetics of the polymerization of 1,3-butadiene initiated by the ternary Ziegler–Natta catalyst system comprising neodymium versatate (NdV), diisobutylaluminium hydride (DIBAH) and ethylaluminium sesquichloride (EASC) have been studied in order to quantify the impact of the catalyst components EASC and DIBAH on the polymerization rate, the control of molar masses, the molar mass distributions as well as on the microstructure of the resulting polymer (cis-1,4, trans-1,4 and 1,2 content). A further focus of the work was on the elucidation of the living nature of the polymerization. It has been found that the catalyst component EASC influences the reaction rate and the microstructure of the obtained polybutadiene. The main effect of the variation of DIBAH is on the molar mass, but the polymerization rate and the microstructure are also influenced. Straight lines are obtained for the dependence of the molar masses on monomer conversion revealing the living nature of the polymerization. The theoretically predicted molar masses are significantly higher than those experimentally found. This discrepancy is explained by the existence of dormant species resulting from the reversible transfer of living polymer chains from Nd onto Al. Only one third of the DIBAH which is not consumed by the processes of scavenging of impurities and activation of the Nd catalyst, is involved in this transfer reaction. This makes DIBAH an inefficient chain control agent for the experimental conditions applied (namely 60°C). A reaction scheme is put forward which accounts for the features observed.