Mechanism of cyclopolymerization. Conformational analysis of cis‐1,3‐diisocyanatocyclohexane

In 1,3‐disubstitued cyclohexanes, in general, the diaxial conformation of the cis isomer is, energetically, the least favored conformation. An interspacial electronic interaction in the ground state of a cis‐1,3‐disubstituted cyclohexane would be expected to increase the proportion of this conformer in the equilibrium mixture. Such an interaction would provide an energetically favorable pathway for cyclopolymerization. From nuclear magnetic resonance studies on cis‐and trans‐1,3‐diisocyanatocyclohexane the conformational equilibrium in the cis isomer was determined. It is shown that cis‐1,3‐diisocyanatocyclohexane exists in the diequatorial conformation; this is taken as evidence that a ground‐state interaction between isocyanato groups in this monomer, which readily cyclopolymerizes, is not a significant factor in the cyclopolymerization mechanism. The value of the free energy barrier, ΔG‡, for trans‐1,3‐diisocyanatocyclohexane was calculated as 11.1 kcal/mole.