Curing behavior and properties of 4,4'-bismaleimidodiphenylmethane and o,o'-diallyl bisphenol a: Effect of peroxides and hybrid silsesquioxane addition

The aim of this work is to provide a better understanding on the use of common organic free radical initiator and hybrid silsesquioxane on curing behavior, corresponding cured structures and thermal mechanical properties of organic bismaleimide (BMI) network consisted by 4,4'-bismaleimidodiphenylmethane (BMPM) and O, O'-diallyl bisphenol A (DABPA). Three kinds of peroxide, Dicumyl Peroxide (DCP), 2,5-Dimethyl-2,5-di(tert-butylperoxyl) hexane (Trigonox ®101), 3,6,9-Triethyl-3,6,9,-trimethyl-1,4,7-triperoxonane (Trigonox ®301) and two types of silsesquioxane, Octastyrenyl (OSTS) and N-Phenylaminopropyl cage mixture (APS) were investigated with BMI system. Specifically, onset of cure reaction and evolution of exothermic heat flow by the differential scanning calorimetry were used to study changes in the reaction mechanism when different initiators and/or silsesquioxane was added. Thermal mechanical properties of cured network, glass transition temperature and degradation kinetics were investigated as a function of additive types and concentration. The result of this work showed that Trigonox® 101 was the most suitable initiator for BMPM/DABPA system due to its low onset curing temperature, around 130oC and mild initiation step which did not result in high homopolymerization rate of BMPM as compared to DCP. Glass transition temperature of BMPM/DABPA with 0.3wt% Trigonox® 101 was significantly improved, 90oC higher than the systems without addition of peroxide additive.;To improve thermal stability of BMI thermoset network, hybrid silsesquioxanes were added into the system. OSTS is a cage (SiO1.5)8 containing eight styrenyl functional groups surrounding the SiO core. The styrenyl functional groups of OSTS can react with BMPM through the free radicals formed by BMPM when heated to around 200oC. APS is a cage mixture of (SiO1.5)n, where n is equal to 8, 10 or 12, with N-aminopropyl groups surrounding the SiO core. APS will react with BMPM at around 150oC through Michael addition reaction. This work showed that this secondary amine in silsesquioxane could effectively react with BMPM forming useful networks. The enhancement in thermal properties, such as glass transition temperature of BMI network by APS was more significant than the OSTS addition. BMI network with only 5wt% APS addition showed an enhancement of 30oC in glass transition temperature while system with 10wt% OSTS showed 20oC increase. Thermo-oxidative degradation rate was also greatly reduced with the addition of hybrid silsesquioxanes.