Examination by d.s.c. of the thermal cure of two aryl bis-maleimides and the corresponding pair of citraconimides, in which the imide groups are attached to the ends of aromatic residues containing four phenylene rings, indicates that the pure bis-maleimides polymerize at lower temperatures than the corresponding citraconimides. A second reaction occurs after polymerization of the pure bis-maleimides has stopped; this appears from FTi.r. to involve residual maleimido groups; pure samples of bis-4-maleimidophenylmethane and bis-4-maleimidophenyl ether also showed this effect. Weight reduction commensurate with evolution of about 1.2 moles of cyclopentadiene occurred on curing the corresponding two bis-nadimides containing four phenylene rings at atmospheric pressure, the extent of this loss being independent of temperature in the range 250-350°C. Resins from the bis-maleimides containing four phenylene rings showed thermal/oxidative stability, measured by t.g.a., similar to that found for resins from bis-4-maleimidophenylmethane and bis-4-maleimidophenyl ether; resins from the bis-maleimides were rather more stable than those from the corresponding bis-citraconimides and bis-nadimides. © 1991.
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