Gregory R. Yandek

Synthesis of Aromatic Polyhedral Oligomeric SilSesquioxane (POSS) Dianilines for Use in High-Temperature Polyimides

A series of novel aromatic Polyhedral Oligomeric SilSesquioxane (POSS) dianiline molecules has been synthesized for use in the preparation of high temperature aromatic polyimides. A general synthetic strategy was devised to improve the structure, yield, and utility of POSS dianilines over those currently available. Peripheral aromatic functionality was specifically incorporated in order to improve thermal properties and to increase compatibility with aromatic polymers. Silyloxy and/or aromatic functional groups were used to link the aniline groups to the POSS cage in order to ensure that this linkage was not a thermal weak point. Additionally, the stereochemistry of the aniline functionality has been varied to produce both meta- and para- isomers. The new dianiline monomers can be used to produce high molecular weight polyimide polymers. These dianilines have been incorporated both as pendants to the polymer backbone, and in a “bead-on-a-string” fashion by insertion into the polymer main-chain. In addition to producing POSS polyimides with superior thermal stability, these new monomers will allow full characterization and comparison of POSS-polyimides with differing structures in order to delineate the structure-property relationships of POSS and polymer architectures.

Polyimides with attached chromophores for improved performance in electro-optical devices

A method of chemical synthesis that allows for the facile attachment of a wide variety of chemical compounds, including highly active nonlinear optical chromophores, to polyimides has been developed recently at the Naval Air Warfare Center, Weapons Division. The synthesis of these compounds is presented, along with a discussion of their relevant physical and chemical properties, alone and in comparison to equivalent guest/host materials. Examples of attached chromophores include the well-known Disperse Red 1, along with high-activity chromophores of more recent interest such as FTC and CLD. The synthesis of structures that contain both attached chromophores and chemical functionalities that enable thermal cross-linking of the polyimides is also discussed.

Synthesis and characterization of a high temperature thermosetting polyimide oligomer derived from a non-toxic, sustainable bisaniline

PMR-15 is a high temperature thermosetting polyimide oligomer widely used in aircraft engines, rocket casings, bushings, and bearings. Unfortunately, PMR-15 is prepared from the mutagenic and hepatotoxic compound methylene dianiline (MDA). To develop a safer alternative to PMR-15, an alternative thermosetting polyimide oligomer (PMR-PCy) was prepared from a less toxic bisaniline, 4,4′-methylenebis-(5-isopropyl-2-methylaniline) (CDA), derived from the renewable aromatic compound p-cymene. The thermoset network prepared from PMR-PCy had a glass transition temperature (Tg) of 323 °C as measured by differential scanning calorimetry (DSC), good thermo-oxidative stability, and water uptake of only 3% after immersion in boiling water for 24 h. The Quantitative Structure Activity Relationship (QSAR)-predicted low toxicity of CDA was confirmed by in vitro testing for mutagenicity, acute toxicity, and aquatic toxicity. CDA was found to be non-mutagenic in the Ames test, had a predicted LD50 of 725 mg kg−1 in rats, and an EC50 of 299.3 mg L−1. These results suggest that CDA is not acutely toxic to humans and has minimal to no aquatic toxicity. The combination of exceptional material properties coupled with the low toxicity of CDA suggest that PMR-PCy may be a viable non-toxic replacement for PMR-15 in a variety of aerospace applications.

Bis-phenylethynyl polyhedral oligomeric silsesquioxanes: new high-temperature, processable thermosetting materials

Bis-phenylethynyl polyhedral oligomeric silsesquioxane (bis-PE-POSS) compounds were synthesized and thermally cured yielding crosslinked materials. After curing at 370 °C, thermal decomposition occurs near 600 °C under nitrogen. These materials were synthesized by condensation of a new phenylethynyl-functional dichlorosilane onto tetrasilanol phenyl POSS, yielding two geometric isomers.

Multifunctional polyimides for tailorable high-performance electro-optical devices

Progress in the development of a new class of multi-functional polyimides for use in electro-optical devices is reported. These polyimides contain hydroxymethyl-functional side-groups attached to the polymer backbone, allowing for the attachment of a wide variety of molecular species. It is shown that multiple types of organic molecules may be attached to the polymer simultaneously, with a quantitatively controllable distribution, to tailor the physical properties of the material. Methods for cross-linking the polyimides are presented, based on both modification to the backbone and the addition of difunctional additives (such as isocyanates) to solutions of the polymer during spin casting. Processing studies using spectroscopy to track the cross-linking reaction and its effects on organic nonlinear optical materials indicate that the latter method is compatible with poling processes for polymer guest/host systems with high nonlinear optical activities. Further studies using a novel thermomechanical analysis method demonstrate that the cross-linking reactions increase the glass transition temperature and inhibit physical relaxation processes in the cross-linked guest/host films.