Soluble and thermoplastically processable fully cyclized BTDA-DDS based polyimide homopolymers and multiphase poly(imide-siloxane) segmented copolymers with controlled molecular weight and non-reactive end groups were synthesized via solution imidization. Adhesive properties were investigated using melt-laminated, single-lap-shear samples prepared from surface-treated Ti-6A1-4V adherends and compression-molded adhesive films. Tests were conducted at room temperature, 100, 150, 200, and 250°C. The room-temperature adhesive bond strengths increased with poly(dimethylsiloxane) oligomer incorporation up to 30 weight percent and were optimum with the lowest controlled molecular weight range investigated (20,000 gm/mole). Lap shear values at 25[ddot] C as high as 50 MPA (7,000 psi) were obtained. The results suggest that melt flow and bond consolidation were critical parameters directly correlated with the lap shear strength. TMA penetration-temperature measurements were consistent with this view. As the test temperature was increased, the homopolymer and 10%-siloxane copolymer showed maximum bond strengths at 200 and 150°C, respectively, while 20% and 30% siloxane-modified copolymers demonstrated decreasing bond strength, relative to their room temperature values.
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Yoon et al. (1992) studied this question.
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