High‐performance bismaleimide matrices: cure kinetics and mechanism

Kinetics and mechanism of equifunctional 4,4′‐( N , N ′‐bismaleimide)‐diphenylmethane/2,2′‐diallyl‐bisphenol A (BMDM/DABPA) and model (phenylmaleimide/2,2′‐diallylphenol) (PMI/AP) systems have been studied in the temperature range 140–400 °C using IR‐, 1 H‐ and ­ 13 C‐NMR spectroscopy, gas chromatography–mass spectrometry GCMS), differential scanning calorimetry (DSC) and isothermal calorimetry. It was established that the cure mechanism consists a unique combination of step‐wise and chain polymerization and polycondensation reactions: step‐wise “ene” addition reaction of allyl group to maleimide one and consecutive/parallel chain polymerization of maleimide and propenyl groups generated by first reaction. The latter reaction is the main crosslinking reaction. The second source of crosslinking is a dehydration reaction of phenol groups that proceeds with mandatory participation as one of the component 1:1 adduct (product of step‐wise polymerization). Homopolymerization of maleimide groups proceeds autocatalytically under the action of free radicals generated by thermal decomposition of maleimide‐propenyl groups' donor–acceptor pairs. Steric hindrance in 2,2′‐diallyl‐bisphenol A prevents the reversible Diels–Alder reaction but this reaction proceeds in model systems. Some thermodynamic and kinetic parameters of the reactions are determined.