Adhesive Characteristics of Alder-Ene Adduct of Diallyl Bisphenol a Novolac and Bisphenol a Bismaleimide

Abstract

Diallyl bisphenol A–formaldehyde copolymer (ABPF) was addition cured with bisphenol A bismaleimide (BMIP) making use of the Alder-ene reaction at high temperatures. The lap shear strength (LSS) of the system was found to depend on the conditions of cure and the stoichiometry of the reactants. Moderate cross linking achieved at a 1:1 maleimide:allylphenol stoichiometry and a stepwise cure, up to a maximum of 250 °C for 2 h, was found to be the most effective in achieving the optimum LSS properties. The system exhibited greater than 100% retention of the LSS at temperatures up to 250 °C. Matrix modification using polysulfone (PS) and polycarbonate (PC) resulted in a remarkable improvement in the adhesive characteristics, although the high-temperature retention was marginally adversely affected. The performance advantage both at room temperature (RT) and at high temperature was greater in the case of PS modification, showing an optimum improvement at 20% loading as against PC modification, exhibiting maximum properties at 10% loading. Scanning electron microscopy (SEM) analysis confirmed that the fine dispersion of PS, rather than large size nodules found in PC, was conducive for the better performance of the former. Dynamic mechanical analysis (DMA) corroborated the observations made in SEM. The existence of co-continuous phases of thermoplastic, matrix and thermoplasticdissolved matrix was evidenced in the PS modification and a clear phase separation was evident in the case of the PC modified system, manifesting independent glass transitions by the individual phases.