Diphthalonitrile compounds of formula I:
Ar.sup.1(CN).sub.2OAr.sup.2CH.sub.2OSi(R.sup.1)(R.sup.2)O-[T-OSi(R.sup.1)(R.sup.2)O-].sub.nCH.sub.2Ar.sup.3OAr.sup.1(CN).sub.2(I)
in free or salt or solvate form, wherein: Ar.sup.1 is a C.sub.6-C.sub.10-aryl group; Ar.sup.2 is a C.sub.6-C.sub.10-aryl group; R.sup.1 and R.sup.2 are independently C.sub.5-C.sub.10-alkyl; T is a C.sub.6-C.sub.10-aryl group; and n is 0, 1, 2, 3, 4 or 5, or a mixture thereof; Cured diphthalonitrile thermosets are provided by curing resin blends of such compounds.

Diphthalonitrile compounds of formula I:
Ar.sup.1(CN).sub.2OAr.sup.2CH.sub.2OSi(R.sup.1)(R.sup.2)O-[T-OSi(R.sup.1)(R.sup.2)O-].sub.nCH.sub.2Ar.sup.3OAr.sup.1(CN).sub.2(I)
in free or salt or solvate form, wherein: Ar.sup.1 is a C.sub.6-C.sub.10-aryl group; Ar.sup.2 is a C.sub.6-C.sub.10-aryl group; R.sup.1 and R.sup.2 are independently C.sub.5-C.sub.10-alkyl; T is a C.sub.6-C.sub.10-aryl group; and n is 0, 1, 2, 3, 4 or 5, or a mixture thereof; Cured diphthalonitrile thermosets are provided by curing resin blends of such compounds.