Kinetic determination of stereoselectivity in the anionic polymerization of α-ethyl-α-phenyl-β-propiolactone

The kinetics of the anionic polymerization of optically active α-ethyl-α-phenyl-β-propiolactone (optical purity 16,8%) initiated with bis(triphenylphosphine)iminium acetate was investigated and the rate constants for the homo-(k_ph) and crosspropagation (k_pc) (considering R and S enantiomers as comonomers) were determined. The knowledge of the values of k_ph and k_pc, equal to 1,53·10^?4 and 9,0·10^?51· mol^?1·s^?1, respectively (25°C, CH₂Cl₂ solvent), allowed us to calculate the distribution of homosequences in the polymer prepared from racemic monomer. The concentration of homosequences was slightly higher than calculated for the process with random enchainment of enantiomers. Thus, the content of homodyads, homotriads, and homotetrads equals 63, 40, and 25%, whereas for the random process it was 50, 25, and 13%, respectively. This difference is, however, too small to create homoblocks which could be responsible for the observed crystallinity of these polymers.