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This paper is concerned with (a) the thermodynamic and kinetic binding sites for Cr(0) in polyimides, and (b) the application of the binding of metals to specific sites on the polyimide backbone to the synthesis of polymer trapped chromium and iron oxide nanoclusters (size < 1.5 nm). In the first part, the organometallic products obtained by the reaction of Cr(CO)3(MeCN)3 or Cr(CO)6 with a number of compounds that mimic the polyimide backbone were identified. A π-arene complex was formed in each case indicating that Cr(0) prefers to form π-arene complexes (even with electron deficient arene rings) rather than react with the oxygen functionalities present. Furthermore, the tendency to form a π-arene complex increases with increasing electron density on the ring. The first part also describes the synthesis and x-ray crystal structure of a charge-transfer complex of Cr(CO)6 with pyromellitic dianhydride — one of the building blocks of polyimides. The second part outlines the synthesis of polyimide-trapped metal oxide nanoclusters. Cr(C6H6)2 or Fe3(CO)12 was added to polyamic acid solutions. Following thermal curing, polyimide films containing a homogeneous dispersion of nanoclusters (size < 1.5 nm) of Cr2O3 or α-Fe(O)(OH) were obtained. Both SEM and SIMS depth profile indicated that the usually observed migration of the dopant to the polymer surface had not occurred.

A series of polyamic-acid polymers with varying molecular weight have been prepared by condensation of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) in N-methylpyrrolidone (NMP). Polyamic-acid solutions between 10 – 20 wt% total solids content were prepared under highly controlled conditions.

Phenylated aromatic polyimides have been prepared in two steps by the Diels-Alder polymerization of biscyclopentadienones with dimaleimides followed by dehydrogenation and in one step by the polymerization of phenylated bis(phthalic anhydrides) with diamines. Although the polymers prepared by both routes were soluble in chlorinated-hydrocarbon solvents, the latter afforded considerably higher molecular weight materials. Polyimides obtained in this manner had intrinsic viscosities as high as 4.0 dl/g and glass transition temperatures that ranged from 238 to 466°C. Thermogravimetric analysis thermograms of the polymers in air and nitrogen atmospheres showed no weight loss until near 530°C. Two new ethynyl-substituted diamines, 4(2,4-diaminophenoxy)phenylacetylene (1) and 3,5-diaminodiphenylacetylene (2), have been synthesized and polymerized with a phenylated bis(phthalic anhydride). The polymer prepared with diamine 1 underwent cross-linking at 250°C without the evolution of volatile byproducts, while the polymer prepared with diamine 2 underwent an analogous cure at 350°C. A phenylated bis(phthalic anhydride) has also been copolymerized with pyromellitic dianhydride (PMDA) and 4,4’-diaminodiphenyl ether to afford soluble copolymers that contain as high as 50 mole % PMDA.

Scanning electron microscopy, electron spectroscopy for chemical analysis (ESCA) and specular reflectance infra-red spectroscopy were employed to characterize titanium alloy (Ti-6A1-4V) surfaces before and after bonding with polyimide resins. Water contact angles on the titanium alloy surface were shown to correlate with surface contamination. Diglyme and DMAC contact angles correlated with fracture strength of the completed adhesive joints formed by the condensation polymerization of benzophenone tetracarboxylic acid dianhydride (BTDA) and m, m’-diaminobenzophenone (m, m’ DABP). Octane/water interfacial contact angles were used to show the presence of polar forces at the adhesive/adherend interface. Variations in adhesive strength were noted for condensation polymers formed in diglyme solutions of (i) BTDA and m, m’ DABP, (ii) BTDA and m, p’ DABP and (iii) m, m’ DABP and pyromellitic dianhydride (PMDA). Scanning electron microscopy was used to observe the titanium alloy surfaces after various pretreatments and the surfaces of fractured joints. ESCA spectra were obtained for the cleaned alloy surface and for fracture surfaces. The intensity of the titanium peak in the ESCA spectra was related to the presence of thin polyimide films. Specular reflectance infrared spectroscopy was also used in the analysis of the fracture surfaces.