THE REACTION OF POLYISOPRENE WITH TITANIUM TETRACHLORIDE

Abstract

The reaction of titanium tetrachloride with hevea, balata, and synthetic cis-polyisoprene in benzene at 80 °C has been studied. The most prominent change in the infrared spectra of these polymers is the nearly total disappearance of the 12 μ band after prolonged reaction with TiCl₄. The diminution of this band, associated with the loss of the original —C(CH₃)=CH— units, whether cis or trans, followed pseudo-first-order kinetics, the rate varying with [TiCl₄]ⁿ, where n is 1.0 in the case of the cis polymers and 1.5 in the case of the trans polymer. Contrary to previous reports, practically no cis–trans isomerization of polyisoprene occurs in the course of this reaction, the data being explained entirely by cyclization. With the help of cis-1,4 polymers of isoprene-3-d and 2-methyl-d₃-1,3-butadiene-1,1-d₂, it was concluded that cyclization, involving a TiCl₄-induced carbonium ion mechanism, leads to the formation of six-membered rings fused into predominantly bicyclic structures, connected by methylene groups and/or uncyclized monomer units. Each of the fused ring structures contains a single tetra-, tri-, or di-substituted double bond, the relative amounts of which are in the order tetra- > tri- > di-substituted.