Synthesis and Adhesion Properties of Polyimdies Containing Diphenylpyrimidine

A series of novel polyimide (PI) copolymers with tailored properties were synthesized via the poly-(amic acid) s (PAAs) from the reaction of 3,3',4,4'-biphenyl tetracarboxylic dianhydride with 4,4-oxydianiline (ODA) and 2,5-his (4-aminophenyl) pyrimidine (PRM). PRM has an extended conjugated rigid rodlike structure containing the pyrimidine group. The effects of the content of PRM on thermal and mechanical properties of the copolymers were investigated. Their glass transition temperatures and the temperatures of 5% weight loss were evidently improved with increase of the molar ratio of PRM to ODA. The tensile strength and modulus of the copolymer films were increased in accordance with the order of the rigidity of the polymer backbones. The value of the coefficient of thermal expansion (CTE) gradually decreased as the PRM content increased. At a molar ratio of PRM to ODA of 1:1, the CTE values of the PI was 17 x 10(-6) K,which was the same value as that of the copper foil. The two-layer flexible copper-clad laminates (FCCLs) were prepared by coating these PAAs solutions onto copper foils and then imidizing thermally. The adhesion strength of polyimide/copper laminate showed peaky curve with the increase of PRM content. While a molar ratio of PRM to ODA at 1:1, the 90 degrees-peel strength of the laminate reached a maximum value of 17.3 N.cm(-1). The flexible structure of ODA and the chemical nature of PRM lead to two-layer FCCL with high adhesion strength as well as thermal-dimensional stability. Furthermore, scanning electron microscope was employed to determine the fracture surface morphology of PI/copper joints.