Synthesis and electronic effect of the substituents on anionic ring-opening polymerization of para-substituted phenyl cyclopropanes

Abstract

As an extension of studies in the anionic polymerization of activated cyclopropanes with electronically push-pull substituents, p-substituted phenylcyclopropane-l,l-dicarbonitriles having MeO, Me, H, Cl, and NO 2 as substituents were prepared. The electronic effects of substituents upon the ring-opening reaction during anionic polymerizations were examined by determining the rate constants of polymerizations, conversions and molecular weights of the resulting polymers. The rate constants of polymerization(k p) in DMSO by 2 mole% cyanide ion at 35°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°C were p-Me0=0.048, p-Cl=7.6 × 10 −3 and p-NO 2 =1.64 × 10 − 3 liter/mole.sec. , respectively. The electronic effect exerted by substituents were well consistent with the Hammett relationship(log k/k o = σ ϱ) when Brown's σ + constants were used. The reaction sensitivity constants(ϱ) obtained from cyanide ion initiator were −1.0 and −0.94 for pyridine initiation. These results indicate that the anionic ring-opening polymerization of p-substituted phenylcyclopropanes is carried out via highly conjugated zwitterionic transition state in the ring opening reaction. Furthermore, in the case of the polymerization initiated by pyridine or triethylamine, the formation of macrozwitterion during polymerization is a feasible mechanism. As an extension of studies in the anionic polymerization of activated cyclopropanes with electronically push-pull substituents, p-substituted phenylcyclopropane-1,1-dicarbonitriles having MeO, Me, H, Cl, and NO 2 as substitutents were prepared. The electronic effects of substituents upon the ring-opening reaction during anionic polymerizations were examined. The rate constants of polymerization (k p) in DMSO by 2 mole% cyanide ion at 35°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°C were p-MeO=0.048, p-Cl=7.6 × 10 −3 and p-NO 2=1.64 × 10 −3 liter/mole.sec. The electronic effect exerted by substituents were well consistent with the Hammett relationship (log k/k o= σ ϱ) when Brown's σ + constants were used. The reaction sensitivity constants (ϱ) obtained from cyanide ion initiator were −1.0 and −0.94 for pyridine initiation. These results indicate that the anionic ring-opening polymerization of p-substituted phenylcyclopropanes is carried out via highly conjugated zwitterionic transition state in the ring opening reaction.