Cationic polymerization of emulsified epoxy resins

Abstract

Whereas free-radical emulsion polymerization has been studied extensively, published reports of cationic (i.e., acid catalyzed) polymerizations of emulsified monomers of any type are rare, and we have found no reported examples of non-reversible emulsion polymerizations catalyzed by Brønsted acids. We recently discovered that treatment of an emulsion of liquid epoxy resin with select superacid catalysts yields polymeric polyols. Catalysis with 1% perchloric acid at room temperature yields a product with a number average molecular weight of 1650, and a polydispersity of 5.0 as measured by gel permeation chromatogram. The polyol’s structure differs from that of conventional high molecular weight epoxy resins prepared by the advancement process in several ways, including the incorporation of two glycidyl units in the repeat unit. The molecular weight of the product depends on the superacid catalyst employed. The product was shown to be much lower in levels of residual bisphenol-A diglycidyl ether (BADGE) and bisphenol-A than conventional epoxy resins, which is an issue of significant importance to producers of can linings for foods and beverages. Polyols prepared by this process were cross-linked with melamine–formaldehyde resins to produce water-borne coatings free of added cosolvent that develop excellent solvent resistance at lower bake temperatures than traditional epoxy resins.