Abstract
The cure kinetics and activation energy (Ea) of bismaleimide homopolymer and modified bismaleimide resin systems with different chain extenders were investigated. The bismaleimide resin under investigation was bismaleimidodiphenyl methane (BMPM) and the chain extenders were (i) O-O′ diallyl bisphenol A (DABA) and (ii) methylenedianiline (MDA). Dynamic multiheating DSC method was used to study the kinetics of the curing process. Activation energies were determined for both unmodified and modified resins from nonisothermal multiheating rate DSC tests by using Ozawa and Kissinger models. Activation energy for BMPM homopolymer increased from 95 kJ/mol to 125 kJ/mol as a function of conversion. For the MDA-modified system the activation energy was independent of percentage conversion, at 108 kJ/mol. In the case of DABA-modified bismaleimide the activation energy increased steadily at 6 kJ/mol from 10 to 100% conversion.
Highlights
High performance thermosets are of great interest as matrix resin for composites
These three heating rates were chosen based on the guidelines of the model-free kinetics (MFK) model and in order to ensure reliable understanding of the cure kinetics
The differential scanning calorimeter (DSC) thermograms show three principal regimes: (a) bismleimidodiphenyl methane (BMPM) neat resin and BMPM/MDA are fine crystalline powders and BMPM/diallyl bisphenol A (DABA) is a highly viscous liquid at room temperature, which upon heating melts showing an endothermic peak, (b) the second regime, is the onset of curing, which is broad and is predominantly chemically driven process, and in (c) the third regime, there is a distinct change in heat flow due to combined effect of kinetics and the inherent exothermic reaction resulting in peak temperatures
Summary
High performance thermosets are of great interest as matrix resin for composites. Bismaleimide- (BMI-) and Polyimide(PI-) based systems are among the more thermally stable thermosetting resins that are fast replacing the widely used epoxy resins. The unique properties of BMI resins, such as low moisture absorption, high crosslink density, good chemical resistance, and high glass transition temperature (Tg) make these resins suitable for prepregs, adhesives, electrical packaging, and other composite applications [1,2,3]. The properties they exhibit are directly related to the microstructure, with high cross-linking density, inherent aromatic structure and rigid molecular network. These microstructural characteristics results in inherent brittleness of the material. Extensive research is being done to enhance the toughness of BMIs by reducing the crosslink density, methods include the addition of reactive elastomers, copolymerization with allyl terminated copolymer, eutectic mixtures and modification with thermoplastics, or a combination of these methods [4]
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