Bismaleimide Resin Powder (4,4'-BMI, High-Temperature Monomer)

Bismaleimide Resin (4,4'-bismaleimidodiphenylmethane, BMI, CAS 13676-54-5) is the standard difunctional BMI monomer for high-temperature thermoset applications. The maleimide groups polymerize via addition mechanism at 150-200°C without releasing volatile byproducts, yielding a highly cross-linked aromatic imide network with Tg of 280-320°C — significantly higher than the best epoxy systems (Tg <230°C).

Pure BMI monomer is a yellow crystalline powder (melting point 155-160°C) that melt-processes or dissolves in solvents (DMF, NMP, acetone) for prepreg and solution impregnation. The neat resin is brittle (KIc ~0.5 MPa·m0.5) and requires toughening through co-reactants: (1) diaminodiphenylmethane (DDM): classic toughening co-monomer at 30-40% by weight — reacts with BMI at 150-160°C to extend chain; (2) epoxy novolac (epoxy-novolac-f44): hybrid BMI/epoxy blends at 20-40% epoxy improve toughness while sacrificing some Tg; (3) allylphenyl compounds (DABA, eugenol): reactive tougheners via Diels-Alder mechanism.

BMI is the choice when epoxy maximum Tg (200-230°C) is insufficient for the application: aerospace engine structures above 200°C, military aircraft high-temperature zones, primary structural elements in supersonic aircraft, and radar-transparent composites requiring high-temperature stability. BMI composites are processable in standard 177°C autoclave infrastructure — unlike polyimide (PMR-15) which requires >300°C processing.