Electron-beam curing of bismaleimide-reactive diluent resins
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abstract
Electron-beam (E-beam) curing of 4,4'-bisBMPMmaleimidodiphenylmethane (BMPM)/BMI-l,3-toly1/o,o'-di-allylbisphenol A (DABPA)-based bismaleimide (BMI) systems and their mixing with various reactive diluents, such as N-vinylpyrrolidone (NVP) and styrene, were investigated to elucidate how temperature, electron-beam dosage, and diluent concentration affect the cure extent. The effect of free-radical initiator on the cure reactions was also studied. It was found that low-intensity E-beam exposures cannot cause the polymerization of BMI. High-intensity E-beam exposures give high reaction conversion attributed to a high temperature increase, which induced thermal curing. It was shown that the dilution and activation of NVP in BMI cause a more complete BMI cure reaction under E-beam radiation. BMI/NVP can be initiated easily by low-intensity E-beam without thermal curing. FTIR studies indicate that about 70% of the reaction is complete for BMI/NVP with 200 kGy dosage exposure at 10 kGy per pass. The sample temperature only reaches about 75C. The free-radical initiator, dicumyl peroxide, can accelerate the reaction rate at the beginning of E-beam exposure, but does not affect the final reaction conversion. The increase of the concentration of NVP in the BMI/NVP systems increases the reactive conversions almost linearly. 2004 Wiley Periodicals, Inc.
