Studies On Modification Of UP With Liquid Crystal Thermoset Bismaleimide

Bismaleimid resins have high thermal stability and excellent mechanical properties and can be used as matrix resins for advanced composites. They have become one of the important high-temperature polymers currently being considered for applications in elevated temperature operations for which conventional epoxy systems may not be sufficiently stable. Because of these predominant properties of bismaleimid, they are applied widely advanced composite for aerospace industries, multiplayer printed circuit boards for large scale computers, structural adhesives, potting resin, etc.In this work, two liquid crystal bismaleimide containing ester bonds ( I a, II a) has been synthesized and characterized by Fourier transform infra-red (FT-IR) spectroscopy, Differential scanning calorimetry (DSC) and 'H-NMR spectroscopy. Nematic liquid crystalline behaviour was observed in hydroquinone bismaleimide ester and its three adducts with hot stage polarized light microscopy(HSPM).In recent years, the thermosetting materials have received increasing attention in industry. Unsaturated polyester (UP) resin is one of the most widely used thermosetting materials since they are relatively inexpensive and offer advantages such as being light in weight and possessing reasonably. But the mechanical properties of composite material and the heat-resistant was low, thus modification of UP resin was necessary.In order to improve ultimate properties, the second component can be added. In present, bismaleimide was used as a second reactive part. The choice of the bismaleimide is due to its very high rigidity and high glass transition temperature. In this present contribution two liquid crystal bismaleimide (Ia, IIa) and 4,4'-bismaleimidodiphenylmethane as a second reactive monomer react to unsaturated polyester (UP) resin, respectively. The blends have beencharacterized in terms of mechanical, thermal and morphology properties by tensile, bend, impact testing, TGA, HDT, DMA, and SEM. The results indicate that the addition of bismaleimide not only improves its properties but also accelerates the polymerization process.But owning to its rigid structure, bismaleimide resins have high melting point, bad solubility, high curing temperature. And another major disadvantage of bismaleimide resins is their brittleness, which limits its possible practical application. Brittleness of polymers has been overcome by chain-extended bismaleimide prepolymer molecules modification, which was prepared by Michael addition reaction of bismaleimides with diamines. While in order to increase the solubility, monomers with polar groups in the amine or anhydride molecules (as starting materials) were used.In this work, the thermosetting adducts based on 4,4'-bismaleimidodiphenylmethane and two liquid crystal bismaleimide ( I a, II a) have been modified by 4,4'-diaminobiphenylether addition. The adducts are characterized by FT-IR , HSPM , DSC and TGA. It is observed that the melting point and curing temperature of the adducts are lower than that of bismaleimide monomers. And the bismaleimide/diamines copolymers are added into UP resin as the second component, the results indicated that the mechanical properties of bismaleimide/diamines/UP copolymers is improved, and the adducts also have high temperature resistance.Fourier transform infra-red (FT-IR) spectroscopy is used to monitor the cure kinetics of these complex system. The available spectroscopic evidence indicated that both the mechanism and the kinetics of the crosslinking process are strongly affected by the presence of the bismaleimide in the system. The addition of bismaleimide to UP resin accelerated the polymerization process.The non-isothermal curing kinetics of bismaleimide /UP resin is studied with DSC. The reaction heats and degree of curing at different heating rates are evaluated. The reaction heats at different heating rates are close to a constant. The energy of activation E and the reaction order n are presented based on Kissinger and Crane equations. The results indicate the cure reaction is 1st-order rea...