Synthesis of high purity o-cresol novolac epoxy resins

O-cresol novolac epoxy resins are used widely as electronic encapsulating materials. When the pitch wires in electronic systems are more slender, there are pressing demands for high purity o-cresol novolac epoxy resin which are with little content of hydrolyzable chloride. In this paper, o-cresol novolac resin was synthesized from para-formaldehyde and o-cresol in the presence of a mixed catalyst (oxalic acid and another co-catalyst). Then, the resultant resin was further reacted with epichlorohydrin to prepare o-cresol novolac epoxy resin. The performances and structure of o-cresol novolac resin and o-cresol novolac epoxy resin were characterized by epoxy equivalent weight, softening point, the content of hydrolyzable chloride and inorganic chlorine, FTIR, 13CNMR. And the relationships between the performances and the reaction conditions were also studied. The results indicate that, o-cresol novolac epoxy resins were synthesized with certain performances through the adjustment of the reaction conditions, which were suited for the pressing demands for high purity applications.