A study of the cyclohexene-formic acid copolymerization reaction

Abstract

While cyclohexene and formic acid are normally inert to polymerization, an unusual copolymerization reaction between them was reported recently when both iodine and free radical initiator are present. This reaction can lead to a copolymer whose repeat units are an unsaturated polyester and a polyalkene. In the present study, the effect of systematically varying the cyclohexene, formic acid, iodine and tert-butylhydroperoxide concentrations on the copolymer yield, composition and extent of crosslinking was determined. The copolymer composition was determined by comparing the infrared absorption intensities of the ester and alkene groups with measurements on polymers in which the repeat units were only either polyester or polyalkene. The extent of crosslinking was determined by Soxhlet extraction of the polymer samples; the crosslinked polymer is insoluble in methylene chloride. The results of this study showed that the extent of crosslinking in the copoljmerization reaction could be reduced by raising the reactant concentration of iodine, formic acid or tert-butylhydroperoxide or by lowering the cyclohexene concentration. Increased polyester content was favored by lowering the cyclohexene concentration but was relatively uneffected by changing the other reactant concentrations. The polymers studied here had low molecular weights (800-1000) and had a solubility parameter of 8,6-10°0 in poorly hydrogen bonded solvents and 9•1-10•8 in moderately hydrogen bonded solvents. Several possible mechanisms were considered for the copolymerization reaction. The results of this study and previous work support a mechanism in which the main step involves the formation of an allylic cyclohexenyl radical (probably as an iodine complex) by hydrogen atom abstraction from cyclohexene by iodine atoms, These radicals can then couple with each other to form a polyalkene or can couple with a formic acid radical to form a polyester.