Modeling of polymerization rate and microstructure in the anionic polymerization of isoprene using n-butyl lithium and N,N,N′,N′-tetramethylethylenediamine considering different reactivities of the structural units

Abstract

A mathematical model for the anionic polymerization of isoprene using n-butyl lithium (n-BuLi) as initiator and N,N,N′,N′-tetramethylethylenediamine (TMEDA) as microstructure modifier, considering a system similar to a tetrapolymerization and a scheme of reaction that considers that the active sites are different in configuration, has been developed. Experimental data of conversion versus time and structure development (1,4-cis, 1,4-trans, vinyl or isopropenyl units) were taken from the literature. Since 1,4-cis structural units are difficult to measure, directly, we used reports based on indirect measurements for natural polyisoprene. The cis structural unit fraction was varied from 0.1 to 0.9 (referred to cis+trans content) in order to provide enough data for parameter estimation purposes. Rate expressions for monomer consumption as well as microstructure and dyad development were obtained from the proposed scheme of reaction. The fraction of active sites and dyad distribution were calculated using Markov chains theory, based on conditional probabilities. The kinetic model correctly describes the performance anionic polymerizations with and without TMEDA.