LaRC ™-SI: A Soluble Aromatic Polyimide

Abstract

LaRC^™-SI (NASA Langley Research Center-Soluble poly Imide) is a wholly aromatic, high-performance thermoplastic with a unique combination of physical, mechanical and adhesive properties. LaRC^™-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^™-SI is its initial solubility in conventional high-boiling aprotic solvents. However, when exposed to temperatures above its softening point of 250 °C it becomes insoluble yet retains its melt processability. This allows LaRC^™-SI to be solution processed as both a polyamic acid and a polyimide. In addition to this solubility characteristic and high softening point, LaRC^™-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^™-SI has been used as a 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 °C.

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