The present invention relates to compounds according to formula (I) and to heat-curable compositions based on polymaleimide resin systems comprising such compounds as co-monomers: wherein R1 is hydrogen or an alkenylphenoxy group, R2 is an alkenylphenoxy group, and R3 is hydrogen or an alkyl group with 1 to 4 carbon atoms. The present invention also relates to cross-linked resins obtainable by curing such compositions. Compounds of the present invention can be used amongst others in fields like structural adhesives, matrix resins for fiber prepregs, moulding compounds, as well as structural and/or electrical composites.