Ring-opening polymerization driven by stabiliza-tion energy

Abstract

p-Substituted Phenylcyclopropanes: In the anionic polymerizations of 2-phenylcyclopropane-1,1-dicarbonitriles by cyanide ion, a mechanism involving zwitterionic transition state was proposed in the previous work. As an extension of studies in the anionic polymerization of activated cyclopropanes by nucleophiles, we examined the polymerization of p-substituted phenylcyclopropane-1,1-dicarbonitriles having MeO, Me, H, Cl, and $NO_2$ as substituents, and the electronic effect upon the ringopening reaction involved in the anionic polymerization were treated quantitatively by determining the rate constants of polymerizations, conversions and molecular weights of the resulting polymers. A kinetic study of the polymerization has been carried out by means of $^1H$ NMR spectroscopy. The rate constants of polymerization ($K_p$) in DMSO by 2 mole \% cyanide ion at 35$^\circ$C were p-MeO=0.45, p-Me=0.14, p-H=0.07, p-Cl=0.06 and p-$NO_2$=0.011 liter/mole sec, and the rate constants of polymerization in DMSO by 5 mole \% pyridine at 35$^\circ$C were p-MeO=0.048, p-Cl=$7.6\times10^{-3}$ and p-$NO_2=1.64\times10^{-3}$ liter/mole sec, respectively. In the kinetic data of ring-opening polymerization, the electronic effect exerted by substituents followed the Hammett relationship (log k/$k_0=\sigma\rho$) when Brown``s $\rho^+$ constants were used. The reaction constant ($\rho$) obtained with cyanide ion initiator was -1.0 and the reaction constant obtained with pyridine initiator was -0.94. From the above results we can enunciate that the anionic ring-opening polymerization of p-substituted phenylcyclopropanes take place via ion pair mechanism (zwitterionic transition state) in the ring opening reaction. Data of polymerization obtained under various conditions indicate that the anionic ring-opening polymerization proceeded through living system. Furthermore, in the case of the polymerization initiated by pyridine or triethylamine, the formation of macrozwitterion during polymeriz...