Involvement of SupramolecularComplexes in the Capture and Release of Protonic Acids During theCationic Ring-Opening Polymerization of Epoxides.

The kinetics of the cationic ring-opening polymerizationsof epoxide monomers were controlled through the use of supramolecularproton complexes. α,ω-Diglycidyl oligoethylene oxidesbearing multiple ethyleneoxy spacer groups form metastable supramolecularproton complexes with strong Brønsted acids generated eitherby the photolysis of onium salts or by their redox reactions withreducing agents. Trapping of the Brønsted acids by insitucomplex formation results in a delay of the onset ofcationic ring-opening. However, once polymerization begins, the epoxidegroups of the monomer are very rapidly consumed resulting in characteristicallyhighly exothermic autoaccelerated polymerization reactions. Crownethers can also form supramolecular complexes with hydronium ionsderived from the reaction of protonic acids with water and these complexescan be used to modify the kinetic behavior of the cationic ring-openingthermal and photopolymerizations of a variety of epoxide monomers.The ring size of a crown ether has a strong influence on the stabilityof the supramolecular complex formed, and this was shown to have amajor impact on the kinetics of the cationic ring-opening polymerizations. [ABSTRACT FROM AUTHOR]