Kinetic Modelling in Living Polymerizations: the Effect of Modifiers on the Degree of Polymerization in Batch and Continuous Stirred Tank Reactors

Equations for the calculation of the degree of polymerization in \u27modified\u27 living polymerizations (living polymerizations in the presence of deliberately added terminating and transfer agents) are developed from a mechanistic/kinetic model. It is shown that a modifier, acting by the mechanism discussed, would cause more chain transfer in a continuous stirred tank reactor (CSTR) than in a batch. This is found to be the case in the living polymerization of 1,3-butadiene initiated by butyllithium in nonpolar solvents, such as cyclohexane, when 1,2-butadiene was used as a modifier. Under similar conditions no chain transfer was detected in batch polymerizations, while ≈ 20% transfer was found in a CSTR. The equations developed can be used to calculate the ratio of the rates of propagation and termination, kp/kt. CSTR data yielded kp/kt ≈ 480 at 90°C; re-evaluation of batch data published earlier by Adams et al. for the same system in hexane solvent yields kp/kt ≈ 1250 and 670 at 50° C and 70°C, respectively