Adhesive properties of low-viscosity phenylethynyl (PE) end-capped co-oligomides and co-oligomide blends

Abstract Phenylethynyl (PE) end-capped co -oligomides of molecular weight equal to 4000 g/mol based on 4,4′-(hexafluoroisopropylidene) biphthalic anhydride (6FDA) and para and meta phenylene diamine containing 80/20 and 70/30 molar ratios of para -to- meta - substituents in the repeat unit were synthesized for thermal, rheological and adhesive properties. On the basis of minimum melt viscosity and glass transition temperature, T g , several co -oligomides and co -oligomer/reactive blend systems were selected for adhesive measurements. The co -oligomide PE-6F-PDA-4K (70 p /30 m ) (PE-PI-4 joint system) exhibited the highest tensile lap shear strength (3582) psi of all systems investigated, while joint system PE-PI-8a containing a 80/20mole% blend of PE-6F-PDA-4K (80 p /20 m ) with reactive diluent PE-6F- m -PDA exhibited the lowest tensile lap shear strength (2392 psi). Optical micrographs showed that bonded specimens containing glass scrim cloth between both titanium adherents fail cohesively at the primer/glass scrim cloth interface, while titanium joints which contained no glass scrim cloth failed mostly at the titanium-primer-adhesive interface region. The results clearly demonstrate that titanium to titanium adhesive joints can be fabricated at low pressure (14.7 psi under vacuum) at 370 °C for 1 h from low-viscosity phenylethynyl end-capped co -oligomides.