PURPOSE: To provide an imide functional polyether having excellent toughness and compounded with epoxy, bismaleimide and polyimide resin systems to increase the bending strength thereof to a large extent.

CONSTITUTION: An imino functional polyether (A) has a mol.wt. of 5000-50000 and having a repeating unit represented by formula I {wherein m is an integer of 1-3; x is O, SO or SO2; and R is a functional group represented by formula II or III (wherein Y is CH2, CHCR2, C(R2)2 or CHCH2; R2 is lower alkyl; R is lower alkyl, lower alkenyl group, etc.; and n is 0 or 2]} and pref. has a repeating unit represented by formula IV [wherein x is O or SO2; and R is a functional group represented by formula II or III (wherein R2 is 1-7C alkyl and R1 is 1-4C alkyl, 3-4C alkenyl, etc.)]. An effective amt. of the imino functional polyether of A is mixed with an epoxy, bismaleimide or polyimide resin system to increase the bending strength of the resin system (B).