Resin composition for forming optical waveguide, resin film for forming optical waveguide, and optical waveguide

A resin composition for forming an optical waveguide, comprising (A) a polyhydroxy polyether having an ethylenically unsaturated group on a side chain and an aromatic ring on a main chain, (B) a polymerizable compound having an ethylenically unsaturated group, and (C) a radical polymerization initiator,

• wherein the component (A) has structural units represented by the following general formulae (3) and (2), wherein the polyhydroxy polyether has structural units represented by the general formula (3) in a content of 3 to 70% by mol, and has structural units represented by the general formula (2) in a content of 30 to 97% by mol:
• wherein R36 represents a hydrogen atom or a methyl group;
• X1 represents a divalent group selected from
• wherein R2 to R18 each independently represent a hydrogen atom, a fluorine atom or an organic group having from 1 to 20 carbon atoms;
• Z1 represents a single bond or a divalent group selected from an oxygen atom, a sulfur atom, —CH2—, —C(CH3)2—, —CF2—, —C(CF3)2—, —SO2—,
• wherein a represents an integer of from 2 to 10;
• Y1 represents a single bond or a divalent organic group having from 1 to 20 carbon atoms;
• and Y4 represents a divalent organic group having from 1 to 18 carbon atoms, and
• wherein X2 represents a divalent group selected from
• wherein R19 to R35 each independently represent a hydrogen atom, a fluorine atom or an organic group having from 1 to 20 carbon atoms;
• Z2 represents a single bond, an oxygen atom, a sulfur atom or a divalent group selected from —CH2—, —C(CH3)2—, —CF2—, —C(CF3)2—, —SO2—,
• wherein b represents an integer of from 2 to 10;
• and Y3 represents a single bond or a divalent organic group having from 1 to 20 carbon atoms.