Cyclopolymerization of Conjugated Dienes

The formation of essentially saturated polymers containing fused cyclohexane rings is a characteristic of the polymerization of conjugated dienes under the influence of all cationic or Lewis acid catalysts. The amount of cyclic structures and non-terminal linear unsaturation is dependent upon the electron accepting ability of the catalyst, which may be greatly influenced by the nature of the solvent. The cyclopolymerization generally proceeds to low conversion and then reaches a dormant state. Addition of monomer to the dormant mixture reinitiates polymerization which again attains a limiting equilibrium conversion. The molecular weight increases with conversion. Polymerization in aromatic solvents results in the incorporation of phenyl groups in the polymer structure. Polymers with low intrinsic viscosities have relatively high molecular weights as measured by light scattering. The proposed polymerization mechanism leading to a perhydrophenanthrene structure involves initiation by a 1,2 or 1,4 monomer cation-radical and propagation through a 1,3 polymer cation-radical. INTRODUCTION The polymerization of conjugated dienes with protonic or Lewis acids has been the subject of numerous investigations within the past 50 years. In general, the polymers from butadiene and isoprene were reported to be low molecular weight products, varying in appearance from viscous liquids to brittle solids. The microstructure consisted of predominantly trans-1,4 unsaturation, accompanied by 1,2 unsaturation, with little or no detectable cis-1,4 unsaturation. However, chemical analysis indicated that the total unsaturation was considerably lower than indicated by a normalized infrared analysis wherein the unsaturation was presumed to total 100 per cent. No identification of the structures responsible for the loss in unsaturation was made. STRUCTURE OF CYCLOPOLYDIENES In the course of an investigation of the polymerization of butadiene and isoprene with Ziegler-type catalysts consisting of alkyl or arylmagnesium bromide or triethyl aluminum with titanium tetrachloride, it was noted that the conversion and the nature of the polymer are dependent upon the Mg/Ti and Al/Ti molar ratios1'2 The conversion curves contain two maxima (Figure 1), the first at an RMgX1TiC14 molar ratio of 05—1 or an AiR 3jTiCl4 molar ratio below 1 and the second at an Mg1Ti ratio of 3—5 or Al1Ti ratio of about 1.