The addition of carbalkoxycarbenes to stereoregular unsaturated polymers

Abstract

The reactions of electrophylic addition of carbalkoxycarbenes to cis‐1,4‐polybutadiene and cis‐1,4‐polyisoprene, resulting in the formation of ester‐substituted cyclopropane groups in the polymer chains, were investigated. The conversion of double bonds into the cyclopropane groups is accompanied by a gradual increase in the glass‐transition temperature, tensile strength, and relative elongation at break. Infrared spectroscopic study with the aid of model substances demonstrated that the addition of even unsymmetric carbene does not destroy the stereo‐regularity of the macromolecule. Only a certain transformation of stereoregularity takes place: the cis configuration of the substituents at the carbon‐carbon double bond is replaced with a new type of stereoregularity, characterized by the steric positions of the substituents (including a new one due to the carbene) with respect to the cyclopropane ring. The ozonolysis of modified polybutadiene (30% conversion of double bonds) indicates that the addition of the carbene does not lead to a block distribution of cyclopropane units. The study of competitive reactions of carbene addition showed that the relative rate constant of carbene addition to polymer does not depend on the degree of conversion, and at low degree of conversion is independent of temperature and of the nature of the solvent and is slightly affected by the nature of the catalyst.