1.4- Dimethylenecyclohexane polymers

The synthesis and polymerization characteristics of 1,4-dimethylenecyclohexane are described. Cationic polymerization of this monomer yields relatively low molecular weight polymers containing appreciable amounts of endocyclic double bonds. In contrast to our earlier claim, 1,4-dimethylenecyclohexane does not seem to cyclopolymerize to a significant extent. 

This paper concerns the polymerization behavior of 1,4-dimethylenecyclohexane, I, a monomer that was claimed in an earlier report (9) to polymerize cationically to afford a soluble, essentially saturated polymer that was presumed to have the bicyclic repeating structure II. 

Figure 1. Effect of 1,4-dimethylenecyclohexane concentration on polymer yield for polymerizations conducted at —78°C using CHtCl as solvent and BFS as...

The above reactions can explain the incorporation of units with endocyclic unsaturation into the polymers. The highly hindered endocyclic double bonds present in such structures probably have low polymerization ceiling temperatures and would resist polymerization. They could be difficult to brominate or hydrogenate. It is our failure to appreciate the limited reactivity of endocyclic double bonds in structures such as IV, IX and X that caused us to overlook them in our original investigation (9). This limited reactivity also explains why soluble polymers can be formed in 1,4-dimethylenecyclohexane polymerizations even when cyclopolymerization does not seem to occur. 

It thus appears that the principal structural features found In poly(1,4-dimethylenecyclohexane) can be explained by conventional carbonium ion chemistry. There is no indication that cyclopolymerization occurs in these polymerizations and there is much evidence to indicate that the double bonds present in this diene react independently. Some of them are involved in polymerization reactions, but a large proportion isomerize to relatively stable endocyclic double bonds. Under polymerization conditions where isomerization is favorable, soluble, unsaturated polymers having complex structures are obtained. When isomerization reactions are not favorable (low temperatures, use of Ziegler-Natta catalysts), the double bonds polymerize independently and crosslinked products are obtained. 

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