EFFECTS OF INTRODUCTION OF SILOXANE SEGME NTS ON SINGLE LAP SHEAR-STRENGTH OF THERMOPLASTIC POLYIMIDES

In recent years, several kinds of adhesive films have been developed a nd applied in aerospace and electronic industries. Processability at m oderate conditions, high initial lap shear strength, durability under high humidity and high temperature conditions are major requirement in their applications. Recently, the polyimide adhesives have been also applied in microelectronics and printed wiring boards industries in Ja pan. However, they ought to be processed at high temperature (> 300 de grees C) and pressure (> 20 MPa) due to the low fluidity. In this work , the relationship between structure and single lap shear bond strengt h of various polyimides were studied for developing the polyimides sui ted as film-adhesives with good processability and adhesive strength. It was found that the polyimides derived from 4,4'-carbonyl-diphthalic anhydride (CDPA) and bis[4-(3-aminophenoxy)phenyl]sulfone (BAPSM) exh ibit excellent lap shear strength at room temperature. In addition, va rious kinds of polysiloxane-block-copolyimides were synthesized and ex amined as film-adhesives to study the effects of polysiloxane incorpor ation into aromatic polyimides on the initial lap shear strength. The all of copolyimides containing 10 wt% of polysiloxane were found to ha ve excellent lap shear strength, despite the difference in aromatic co mponents. Their adhesive durability under a highly humid condition (25 degrees C, 90%RH) was also improved mainly due to their lower moistur e sorption and lower moisture permeability. However, further incorpora tion of polysiloxane into polymer backbone gradually lowered the initi al lap shear strength and the durability.