Preparation and properties of molecular-weight-controlled polyimide adhesive film

Abstract

AbstractA series of molecular-weight-controlled aromatic polyimides based on 4,4’-oxydiphthalic anhydride (ODPA), 1,4-bis(4-amino-2-trifluoromethylphenoxy) benzene (6FAPB) and 4,4’-diaminodiphenylsulphone (4,4’-DDS) were synthesized in the presence of phthalic anhydride (PA) as end-capping agent. The effect of molecular weight on solubility, melt viscosity, thermal and mechanical properties of polyimides was investigated. Experimental results demonstrated that these polyimides have good solubility not only in most of polar aprotic solvents but also in some of common organic solvents, such as DMSO and THF. Homogeneous and stable polyimide solutions with solid content as high as 40-45 wt.% could be achieved. High-quality polyimide films could be obtained by casting the polyimide solutions onto glass plate followed by baking at a relatively low temperature. The polyimide films exhibited outstanding thermal and mechanical properties. The rheological behavior of these polyimides depends on their molecular weight. Adhesive properties of polyimide films bonded to stainless steel were evaluated by lap shear strength (LSS) test. The bonding conditions were optimized with respect to the melt temperature, bonding pressure and time, as well as thickness of the adhesive layer. It is found that the polyimides with moderate molecular weight exhibited better adhesive properties.