Novel epoxy resins based on cyclohexanone-aldehyde condensation products


  • Presented by J. A. C. at the 14th International Conference in Organic Coatings Science and Technology, July 1988, Athens, Greece.


Solid ketone-formaldehyde resins are used in certain coating formulations in order to improve hardness, gloss, and light stability. They are soluble, thermoplastic by nature, and contain limited amounts of hydroxyl groups. We found that their primary hydroxyls can be etherified with epichlorohydrin (ECH) either by a two-step ECH-addition/dehydrohalogenation procedure or by a one-step phase-transfer process. An intermediate of particular usefulness is the crystalline 2,2,6,6-tetramethylol-cyclohexanol (TMCH) made from cyclohexanone and 5 mol formaldehyde, yielding low colored epoxy resins with epoxy values up to 7.5 eq/kg. Depending upon the nature of the curing agent, high Tg solids as well as tough and flexible coatings with good outdoor stability can be made. Upon decreasing the formaldehyde–cyclohexanone ratio, solid condensation polymers melting up to 150°C can be obtained. Phase-transfer glycidylation yielded solid thermoset glycidyl ether resins with M̄n up to 1600, M̄ω up to 13,000, epoxy values up to 3.6 eq/kg, and softening points between 80 and 160°C. Powder coatings formulated with carboxyterminated polyesters are hard, glossy, solvent-resistant but somewhat brittle. In order to overcome this drawback, polycycloacetals have been produced from TMCH and glutardialdehyde, which are terminated by pairs of methylol groups. Powder coatings of the corresponding glycidylethers with carboxyl-terminated polyesters exhibited excellent flexibility and impact strength.