One-component novel allyl–maleimide Alder ene resins: synthesis, curing, and thermal properties
Novolac resins, bearing both allyl and maleimide groups in varying proportions and capable of self-curing via Alder ene reaction, were synthesized by anchoring maleimidobenzoyl groups onto allyl novolac resins. These systems are capable of self-curing at moderate temperature by undergoing two-step cure reaction, i.e. ene reaction (~60 °C) followed by Diels–Alder reaction (~180 °C) to form thermal stable resins. Anchoring of the allyl and the maleimide groups in the same molecule decreases the cure activation energy tremendously due to increased proximity of reactive species and favorable activation entropy factors. The increase in activation energy with conversion implied that the reaction migrates from chemically controlled zone to diffusion-controlled zone beyond ~50% conversions. The resins showed increasing thermal stability with enhanced maleimide content.