1,3‐Cyclohexadiene polymers. Part I. Preparation and aromatization of poly‐1,3‐cyclohexadiene

Polymerization of 1,3‐cyclohexadiene was carried out in the presence of initiator systems such as titanium tetrachloride, organoalkali compounds, and Ziegler‐type catalysts. The best results as regards conversion rate and molecular weight, were those obtained with the use of organolithium compounds as initiators. When polymerization is performed in noncomplexing medium, all polycyclohexadienes are comparable, no matter what the initiator system used. They are composed mainly of 1,4‐substituted cyclohexene units and the double bond configuration is cis and trans . The cis – trans isomerization of the double bond seems to be independent of the polymerization mechanism. Complexing or highly polar reaction media favor the 1,2‐linking between cycles. The microstructure of the polymers was determined by infrared spectrometry and nuclear magnetic resonance analysis. Aromatization or partial dehydrogenation of polycyclohexadiene was achieved either by reaction with tetrachloro‐ p ‐benzoquinone or by bromination followed by dehydrobromination. An increase of the bromination temperature results in the direct formation of an aromatized polymer through the evolution of hydrogen bromide as soon as the bromine is fixed to the polymer. Infrared spectral analysis of the aromatized polymers give a further confirmation of two different types of substitution in polycyclohexadiene.