Analysis of the Mechanism of Polybutadiene Synthesis in the Presence of the Neodymium Versatate plus Diisobutylaluminum Hydride plus Ethylaluminum Sesquichloride Catalytic System within the Solution of the Inverse Kinetic Problem

A kinetic model is proposed for polybutadiene synthesis in the presence of the neodymium versatate + diisobutylaluminum hydride + ethylaluminum sesquichloride (NdV + DIBAH + EASC) catalytic system. As a result of solving the inverse kinetic problem, the rate coefficients of reactions were determined. At a quantitative level, it has been shown that polybutadiene synthesis in the presence of the NdV + DIBAH + EASC catalytic system can run according to the scheme, which includes only the chain propagation, chain termination, chain transfer to butadiene, and DIBAH. This fact testifies against the need to involve the reactions of the coordinative chain transfer polymerization mechanism to describe the kinetic regularities of the process in question. Based on the bimodal form of the experimental molar mass distributions of polybutadiene, it was taken into account in the proposed kinetic model that all reactions run on active sites of two types. As a result of the calculation of the characteristic times of chain limitation (in which the chain limitation is a sum of chain termination and transfer rates) on active sites of the first and second types, it was shown that the active sites of the first type are the active sites of classical coordination polymerization (the characteristic time of chain limitation is 3.35 x 101-8.82 x 101 s) and on active sites of the second type, living chain propagation runs. This is due to the fact that the characteristic chain limitation time for active sites of the second type is 9.09 x 103 to 1.35 x 105 s, which is comparable to the time of polybutadiene synthesis until a high butadiene conversion is reached (1.00 x 104 s).