A calorimetric study of the 4,4'-(N,N'-bismaleimide)diphenylmethane-2,2'-diallylbisphenol A system

The kinetics of thermal cure of the 4.4'-(N,N'-bismaleimide)diphenylmethane -2,2'-diallylbisphenol, a system and some model systems involving monofunct ional compounds (N-phenylmaleimide and 2-allylphenol) at different componen t ratios were studied by the DSC and isothermal calorimetric techniques. It was shown that the cure process in the equifunctional system occurs in two temperature regions with maximum rates at 230-240 and 330-340 degreesC cor responding to two major reactions, the condensation of maleimide and allyl groups and the subsequent crosslinking by radical polymerization of the pro penyl groups formed in the first step and unreacted allyl groups. The entha lpy of double bond opening of the maleimide group in its condensation react ion with the allyl group and in the polymerization is equal to 92 kJ/mol fo r both reactions. It was found that the competing reaction in the first ste p is the homopolymerization of maleimide groups, which occurs in the autoca talytic mode and is initiated by the free radicals produced by thermal degr adation of the maleimide group-propenyl group donor-acceptor pair. The role of this reaction increases with increasing the excess of maleimide over al lyl groups in the initial mixture and decreases with increasing the reactio n temperature. The elevation of temperature increases the contribution of t hermally induced homopolymerization of maleimide groups. The reaction kinet ics in the range 140-200 degreesC were shown to be described well with allo wance for competition between the aforementioned reactions. The reaction ra te parameters were: determined for all of the systems examined.