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Abstract

A process for producing a highly reactive modified phenolic resin, comprising the steps of polycondensing a petroleum heavy oil or pitch, a formaldehyde polymer and a phenol in the presence of an acid catalyst to thereby prepare a modified phenolic resin; and reacting the resultant modified phenolic resin with a phenol in the presence of an acid catalyst but in the absence of a crosslinking agent such as a formaldehyde polymer to thereby lower the molecular weight of the modified phenolic resin. This highly reactive modified phenolic resin has a low number average molecular weight and a high phenol content, so that its resin melt viscosity is low and that it exhibits a markedly improved reactivity with an epoxy resin. Accordingly, the combination thereof with an epoxy resin provides a molding material suitable for producing a molding which is excellent in not only thermal resistance and moldability but also dimensional stability and other mechanical properties, especially a material for electrical or electronic part and a semiconductor sealer.

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