Effect of molecular weight on processing and adhesive properties of the phenylethynyl-terminated polyimide LARC™-PETI-5

Three different molecular weight versions of the phenylethynyl-terminated polyimide LARC(TM)-PETI-5 were synthesized. The materials synthesized had theoretical number average molecular weights of 2500, 5000,and 10000 g/mol. Differential Scanning Calorimetry (DSC) was performed on the dry powder form of these materials to establish cure conditions which result in high glass transition temperatures. Lap shear specimens were prepared from adhesive tape made from each material and with the thermal cure conditions determined from the DSC data. The tensile shear data established which processing conditions provided the best adhesive strengths. Titanium tensile shear strengths as high as 52.6 MPa (7630 psi) al RT and 35.2 MPa (5100 psi) at 177 degrees C were determined. Processing temperatures as low as 316 degrees C and pressures as low as 0.17 MPa (25 psi) resulted in good adhesive properties. The tensile shear properties of these materials were unaffected by hydraulic fluid. The molecular weight of LARC(TM)-PETI-5 has an important effect on the bonding pressures required to obtain good tensile shear strengths. The effect of molecular weight on the utility of PETI-5 to be used as a primer to maintain surface quality for bonding was also investigated.