A polyether polymer that is the reaction product of ingredients including: (i) an extender comprising a polyacid; a phenol compound having both a phenol hydroxyl group and a carboxylic group; or a dihydric phenol having the Formula (IV): HO-Ar- (Y u -Ar) t -OH Formula (IV), wherein: each Ar is independently an unsubstituted phenylene group; Y, if present, is a divalent group; u is independently 0 or 1; and t is independently 0 or 1; and (ii) a polyepoxide having the Formula (II): wherein: each R 1 is independently an atom or group having an atomic weight of at least 15 Daltons, and each phenylene group depicted in Formula (II) includes at least one R 1 attached to the ring at an ortho or meta position relative to the depicted oxygen atom; v is independently 1 to 4; w is 4; R 2 , if present, is a divalent group; n is 0 or 1, with the proviso that if n is 0, the phenylene groups depicted in Formula (II) can optionally join to form a fused ring system in which case w is 3 and each v is independently 1 to 3; two or more R 1 and/or R 2 groups can join to form one or more cyclic groups; s is 0 or 1; R 3 , if present, is a divalent group; and each R 4 is independently a hydrogen atom, a halogen atom, or a hydrocarbon group that may include one or more heteroatoms. (i) an extender comprising a polyacid; a phenol compound having both a phenol hydroxyl group and a carboxylic group; or a dihydric phenol having the Formula (IV): HO-Ar- (Y u -Ar) t -OH Formula (IV), wherein: each Ar is independently an unsubstituted phenylene group; Y, if present, is a divalent group; u is independently 0 or 1; and t is independently 0 or 1; and each Ar is independently an unsubstituted phenylene group; Y, if present, is a divalent group; u is independently 0 or 1; and t is independently 0 or 1; and (ii) a polyepoxide having the Formula (II): wherein: each R 1 is independently an atom or group having an atomic weight of at least 15 Daltons, and each phenylene group depicted in Formula (II) includes at least one R 1 attached to the ring at an ortho or meta position relative to the depicted oxygen atom; v is independently 1 to 4; w is 4; R 2 , if present, is a divalent group; n is 0 or 1, with the proviso that if n is 0, the phenylene groups depicted in Formula (II) can optionally join to form a fused ring system in which case w is 3 and each v is independently 1 to 3; two or more R 1 and/or R 2 groups can join to form one or more cyclic groups; s is 0 or 1; R 3 , if present, is a divalent group; and each R 4 is independently a hydrogen atom, a halogen atom, or a hydrocarbon group that may include one or more heteroatoms. each R 1 is independently an atom or group having an atomic weight of at least 15 Daltons, and each phenylene group depicted in Formula (II) includes at least one R 1 attached to the ring at an ortho or meta position relative to the depicted oxygen atom; v is independently 1 to 4; w is 4; R 2 , if present, is a divalent group; n is 0 or 1, with the proviso that if n is 0, the phenylene groups depicted in Formula (II) can optionally join to form a fused ring system in which case w is 3 and each v is independently 1 to 3; two or more R 1 and/or R 2 groups can join to form one or more cyclic groups; s is 0 or 1; R 3 , if present, is a divalent group; and each R 4 is independently a hydrogen atom, a halogen atom, or a hydrocarbon group that may include one or more heteroatoms. <EOS>