ANIONIC-POLYMERIZATION OF ACRYLATES .8. KINETICS OF THE ANIONIC-POLYMERIZATION OF BUTYL ACRYLATE INITIATED WITH THE COMPLEX INITIATOR LITHIUM ESTER ENOLATE LITHIUM TERT-BUTOXIDE

The kinetics of the anionic polymerization of butyl acrylate initiated with the system tert-butyl 2-lithioisobutyrate (Li-t-BIB)/lithium tert-butoxide (t-BuOLi) in the mixed solvent toluene/tetfahydrofuran was studied at -70 to -40 degrees C. At -60 degrees C, the external reaction order is unity with respect to the concentrations of both the monomer and propagating species. Semilogarithmic conversion curves indicate a certain extent of self-temination at higher degrees of conversion. The termination reaction proceeds formally as a first-order reaction with respect to active centers. Kinetic calculations show that while the rate constant of propagation is concentration-independent, the rate constant of termination increases with the initial concentration of the monomer. The temperature dependence of the polymerization was studied for various solvent compositions and various [Li-t-BiB](0)[t-BuOLi](0) mole ratios. In toluene/THF = 9/1 (v/v), the rate constant of self-termination grows more steeply with increasing temperature than the rate constant of propagation so that at -40 degrees C the limiting monomer conversion is approximately 60%. In toluene/THF = 19/1 (v/v), the temperature dependence of the rate constant of self-termination is less distinct than in the former case and the conversion is 90% even at -20 degrees C. From the GPC measurement it is seen that the autotermination proceeds in all referred experiments and only the relation between concurrent propagation and termination reactions is responsible for the formation of the polymer with a narrow MWD under suitable conditions.