Quantitative analysis of bismaleimide-diamine thermosets using near infrared spectroscopy

A method is reported for studying the polymerisation kinetics of a commonly used bismaleimide monomer, 1,1'-(methylenedi-4,1-phenylene)bismaleimide (MDP-BMI) with aromatic diamines such as 4,4'-diaminodiphenylmethane (DDM). Fourier-transform near infrared (FT-NIR) spectroscopy was used to obtain quantitative data using an in-situ technique. The NIR technique was used to measure the concentration of the various functional groups in the BMI/diamine resins with respect to time during isothermal cure. Quantitative data were obtained for all the functional groups in the resins studied, either from direct measurement or from the mass balances involved in the reactions. In order to obtain truly quantitative data, Fourier self-deconvolution of the spectra was used to enhance peak separations and the determination of peak areas. A substantial difference in reactivity between primary and secondary amine was observed in the systems studied. This has significant implications for the modelling of the polymerisation kinetics where the conversions of primary and secondary amines have not been separately measured. Differences in the reactivities of different resin formulations where observed when the diamine was changed from DDM to 4,4'-diaminodiphenylsulphone (DDS). There is a strong suggestion that one of the initial reaction products has a catalytic effect on the reaction, at least when using DDS as the diamine. The most likely identity of the species involved in this self-catalysis is the secondary amine formed by reaction of the maleimide double bond with a primary amine. (C) 2000 Elsevier Science Ltd. All rights reserved.