Composition of epoxy resin, polyphenolic compound and trisubstituted phosphonionphenolate salt

An epoxy resin composition comprising:

• a compound having two or more epoxy groups in one molecule,
• a compound having two or more phenolic hydroxyl groups in one molecule, and a curing accelerator for promoting the curing reaction of the epoxy composition,
• wherein the curing accelerator comprises trisubstituted phosphoniophenolate or a salt thereof, wherein the trisubstituted phosphoniophenolate is represented by the following general formula (2):
• wherein Ar1, Ar2 and Ar3 are the same as or different from one another, and each represents a substituted or unsubstituted monovalent aromatic group;
• and Ar represents (i) an unsubstituted divalent aromatic group or (ii) a divalent aromatic group substituted with a single substituent, said substituent not being a hydroxyl group;
• further wherein in the case when said divalent aromatic group is a phenylene group, the oxyanion-O− is located in an ortho or meta position relative to the phosphorus atom.

An epoxy resin composition comprising:

• a compound having two or more epoxy groups in one molecule,
• a compound having two or more phenolic hydroxyl groups in one molecule, and
• a curing accelerator for promoting the curing reaction of the epoxy resin composition, wherein the curing accelerator comprises trisubstituted phosphoniophenolate or a salt thereof, wherein the trisubstituted phosphoniophenolate is represented by the following general formula (3):
• wherein R4, R5 and R6 are the same as or different from one another, and each is selected from the group consisting of a hydrogen atom, a methyl group, a methoxy group and a hydroxyl group, further wherein the oxyanion-O− is located in an ortho or meta position relative to the phosphorus atom.