Model reactions of calixarenes and their esterified derivatives with glycidyl phenyl ether for thermal curing reactions of epoxy resins

Abstract

Calixarenes (CAs) are perfectly defined cyclic phenolic oligomers with potential applications as curing agents for polyfunctional epoxy resins to prepare cured epoxy resins with high glass transition temperature and high thermal stability. This paper explores the reaction mechanisms and optimal reaction conditions of CAs with epoxy groups by studying the model reactions of calix[4]resorcinarene (CRA), p-tert-butylcalix[n]arene (BCA[n], n=4, 6, 8) and their esterified derivatives with glycidyl phenyl ether (GPE). For reactions of completely esterified CRA with GPE, the optimum reaction conditions were determined as tetraphenylphosphonium chloride catalyst in chlorobenzene at 120 °C for 6 h. Under the above reaction conditions, the degree of introduction of GPE (D.I.) to CRA and its esterified derivatives was greater than 95%, whereas D.I.s were lower than 81% for BCA[n] (n=4, 6, 8) and their esterified derivatives. This difference in reactivity resulted from the difference in intermolecular hydrogen bonding and steric hindrance between CAs. These results indicate that CRA and its derivatives have great potential as curing agents for polyfunctional epoxy resins. Model reactions of calix[4]resorcinarene (CRA), p-tert-butylcalix[n]arene (BCA[n], n=4, 6, 8) and their esterified derivatives with glycidyl phenyl ether (GPE) were examined using tetraphenylphosphonium chloride (TPPC) as the catalyst in chlorobenzene at 120 °C for 6 h. It was found that the degree of introduction of GPE (D.I.) to CRA series was higher than 95%, whereas for BCA[n] (n=4, 6, 8) series, D.I.s were lower than 81%. Therefore, CRA and its derivatives are good potential curing agents for preparing cured epoxy resins with excellent thermal properties.