Synthesis of novolac on the basis of bisphenol A as curing agent for epoxy resins

Abstract

Abstract Bisphenol A novolacs were synthesized in a melting process using paraformaldehyde, and in a solution process using a formalin solution and oxalic acid catalyst. 1 H‐NMR investigations show a higher content of methylene bridges in the novolacs synthesized in a melting process. These novolacs were analysed by HPLC, GPC, DSC and FT‐IR spectroscopy. The molecular masses were determined by vapour pressure osmometry. The results were shown to be related with the molar ratio of the components. The bisphenol A novolacs were used as curing agents for epoxy resins. There exists a dependence of the gel times on the content of methylene bridges; this dependence is influenced by temperature. The activation energy for gel formation is nearly the same in all curing reactions investigated. The networks synthesized were investigated by thermomechanical analysis.