EPOXY NUCLEOPHILE CATALYZED TRANSESTERIFICATION

Epoxy nucleophile catalyzed transesterification (ENCAT) is a new cure technology, which is particularly well-suited for coatings applications. Acrylic and acrylic-polyester blends in high-solids paints self-cure with ENCAT under normal bake conditions to give an excellent balance of hardness, flexibility, and solvent resistance. Powder paints prepared with ester derivatives of epoxy resins self-cure, and likewise give an excellent balance of properties. The ENCAT catalyst is formed during cure by the combination of a nucleophile with an epoxide moiety. A strong base alkoxide, which is produced when the epoxide ring opens by nucleophilic attack, initiates transesterification. This mechanism is supported by C-13 NMR and gas chromatographic studies. Rate of transesterification is related to the structure of the hydroxyl and ester groups undergoing transesterification. Transesterification rate is directly related to the concentrations of the nucleophile and epoxy co-catalysts, as well as to the basicity and nucleophilicity of the nucleophile.