(602b) Cascade Ring Strain Release Polymerization of Cyclohexene Oxide and Derivatives Using Mono(µ-alkoxo)Bis(alkylaluminum) Initiators

Cyclohexene oxide (CHO) is a versatile building block for the synthesis of novel materials and as a model substrate for polymerization catalyst development. The thermodynamic driving force for CHO polymerization is derived from its bicyclic structure which combines the release of the enthalpy from epoxide ring-opening (ca. –15 kcal/mol) and a twist-chair-to-chair conformation shift in the cyclohexane ring (ca. –5 kcal/mol) upon enchainment. The lack of functional handles attached to the CHO monomer limits the ability to both pre- and post-functionalize the resultant materials and establish structure-property relationships, which reduces the versatility of currently accessible materials. We report the synthesis of two series of CHO derivatives with butyl, allyl, and halogen substituents α and β to the epoxide ring. Adding substituents to the CHO ring was found to affect polymerization kinetics, with 4-substituted (β) CHO being more reactive than 3-substituted (α) CHO analogs when initiated with a mono(µ-alkoxo)bis(alkylaluminum) pre-catalyst. Polymer thermal properties depended on substituent location and identity. Halogenated CHO rings were most reactive and produced the highest glass-transition temperatures in the resultant polymers (up to 105 ºC). Density functional theory revealed a possible mechanistic explanation consistent with the observed differences in polymerization rate for the 3- and 4-substituted CHOs derived from a combination of steric and thermodynamic considerations.