LaRC(TM)-SI: A soluble aromatic polyimide

LaRC(TM)-SI (NASA Langley Research Center-Soluble polylmide) is a wholly aromatic, high-performance thermoplastic with a unique combination of physical, mechanical and adhesive properties. LaRC(TM)-SI is synthesized from equimolar amounts of the dianhydrides 4,4'-oxydiphthalic anhydride (ODPA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA); 3,4'-oxydianiline (3,4'-ODA) and phthalic anhydride (PA) as an endcapping reagent. The most unique property of LaRC(TM)-SI is its initial solubility in conventional high-boiling aprotic solvents. However, when exposed to temperatures above its softening point of 250 degrees C it becomes insoluble yet retains its melt processability. This allows LaRC(TM)-SI to be solution processed as both a polyamic acid and a polyimide. In addition to this solubility characteristic and high softening point, LaRC(TM)-SI is extremely tough and fracture resistant with G(1c) and K-1c values of 4.6 kJ m(-2) and 4.4 MN m(-3/2) respectively. As a melt extruded film, LaRC(TM)-SI has been used asa hot melt adhesive to bond titanium and aluminium with lap shear strengths for titanium and cleavage strengths for aluminium exceeding 43 MPa and 16.9 MPa respectively at 23 degrees C.