High Performance Polymers

Imide-aryl ether phenylquinoxaline triblock copolymers were investi gated. A key feature of the copolymer systems is the preparation of a mono-functional amine-terminated aryl ether phenylquinoxaline oligomer via nucleophilic aromatic substitution. The oligomer was co-reacted with various compositions of 4,4'-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in an N- methylpyrrolidone/N-cyclohexylpyrrolidone (NMP/CIIP) solvent mixture in the pres ence of N-methylmorpholine. The resulting amic ester-aryl ether phenylquinoxaline copolymers were isolated and washed to remove homopolymer contamination. Co polymer compositions, analyzed by ¹H-NMR, showed good agreement with that charged. Solutions of the copolymers were cast and cured (350°C) to effect imidization, affording tough and clear films. Multiphase morphologies were observed for the copolymers prepared, and the ordered morphology characteristic of the polyimide homopolymer was retained in the copolymers. In addition, significant improvements in the adhesion characteristics were observed.

Titanium was evaporated onto PMDA-ODA polyimide surfaces at room temperature up to total thicknesses of about five monolayers. The polyimide backbone is ruptured at both the oxygen ether linkage in the ODA and at the nitrogen imide linkage. The first fraction of a monolayer reacts with oxygen atoms in both the carbonyl and ether functionalities, and forms a mixed oxide with titanium predominantly in the Ti⁺³ oxidation state. Near one monolayer coverage, a carbide or mixed oxy-carbide species forms. Above one monolayer, nitrogen is strongly attacked and ~50% of the nitrogen reacts with titanium. The deposited titanium begins to take on metallic character only after the coverage has reached several monolayers. Heating at 575 K causes additional reaction. Scanning tunelling microscopy images obtained in air following heating show that the composite surface is substantially roughened.

PBI (polybenzimidazole) is a thermally stable high performace polymer. In a variety of forms, e.g. fibers, neat resin and composites, PBI finds use in a wide range of high temperature applications. The synthesis of PBI, and properties, and applications of fiber and molded resin are discussed. Also included are recent developments in composite fabrication technology and PBI composite applications in carbonlcarbon composites.

The synthesis, characterization and development of a new generation of fluoro-containing polyamideimide (PAI) polymers are described in this paper. The polymers are generally prepared by forming the polycondensation product of an aromatic diamine, a trifunctional aromatic anhydride acid chloride and an aromatic dianhydride containing trifluoromethyl moieties. These new materials possess high glass transition temperatures, useful mechanical properties and outstanding thermoplastic flow behavior which render them readily melt processable into fibers, films, sheets and other molded articles. The as-precipitated fluoro-containing PAI materials are soluble in many organic solvents and are thus amenable to solution casting techniques. They also show excellent resistance towards thermooxidative degradation at temperatures to 450°F and have low moisture uptake. In addition, compatible blends with polybenzimidazole (PBI) resin have yield synergistic effects on the mechanical properties of the resulting polymer.

Investigation of the influence that monomer structure plays in determina tion of the nature of thermoset PMR polyimides has revealed new information regarding the cross linking reaction profile and resultant resin properties. Replacement of BTDE by ODPE as dianhydride shows reduced resin T _g values. Synthesis of a new series of alkylene dianilines, with increasing flexibility within the homologous series, evinces lowered cross-linking onset temperatures and T _g transitions. Increasing degrees of meta catenation in extended diamines also result in lowered T _g values.

A series of polyimide films prepared from 4,4'-oxydiphthalic anhydride (ODPA) and selected diamines were compared with those from pyromellitic anhydride (PMDA), 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA) and benzophenonetet racarboxylic dianhydride (BTDA). Mechanical, electrical and thermal properties, as well as the chemical resistance of these films, were measured. The data presented in the following paper demonstrate the excellent properties characteristic of ODPA polyimides and the versatility obtainable through the careful selection of the diamine.

Propargyl derivatives of biphenols and phenol-formaldehyde resins (propargyl-terminated resins—PTRs) are being evaluated as non-polar matrices for advanced polymeric composites. The dipropargyl ether of bisphenol A and its B-staged materials are the most attractive candidates. PTR monomers are available in a one-step, easy preparation in quantitative yield from inexpensive starting materials. They are suitable for industrial production in large scale at a potentially low price. PTR thermosets based on different biphenols have a glass transition temperature above 300°C (572°F), and excellent isothermal thermo-stability in air and nitrogen which corresponds to that of the acetylene-terminated resins. In addition, they have low water absorption, low dielectric constant and dissipation factor, excellent physico-mechanical properties, etc. B-staging of PTR proceeds with a rearrangement of the propargyl group into a chromene ring. The final thermosets cure through polymerization of the chromene group. PTRs are a potential low cost substitute for epoxy resins for composites, adhesives, coatings and electronic applications.