Semi-interpenetrating polymer network for tougher and more microcracking resistant high temperature polymers

This invention is a semi-interpenetrating polymer network which includes a high performance thermosetting polyimide having a nadic end group acting as a crosslinking site and a high performance linear thermoplastic polyimide. An improved high temperature matrix resin is provided which is capable of performing at 316 C in air for several hundreds of hours. This resin has significantly improved toughness and microcracking resistance, excellent processability and mechanical performance, and cost effectiveness

A tough high performance composite matrix

This invention is a semi-interpenetrating polymer network which includes a high performance thermosetting polyimide having a nadic end group acting as a crosslinking site and a high performance linear thermoplastic polyimide. An improved high temperature matrix resin is provided which is capable of performing in the 200 to 300 C range. This resin has significantly improved toughness and microcracking resistance, excellent processability, mechanical performance and moisture and solvent resistances

Optically transparent/colorless polyimides

Several series of linear aromatic polyimide films have been synthesized and characterized with the objective of obtaining maximum optical transparency. Two approaches have been used as part of this structure-property relationship study. The first approach is to vary the molecular structure so as to separate chromophoric centers and reduce electronic interactions between polymer chains to lower the intensity of color in the resulting polymer films. A second and concurrent approach is to perform polymerizations with highly purified monomers. Glass transition temperatures of thermally cured polyimide films are obtained by thermomechanical analysis and thermal decomposition temperatures are determined by thermogravimetric analysis. Transmittance UV-visible spectra of the polyimide films are compared to that of a commercial polyimide film. Fully imidized films are tested for solubility in common organic solvents. The more transparent films prepared in this study are evaluated for use on second-surface mirror thermal control coating systems. Lightly colored to colorless films are characterized by UV-visible spectroscopy before and after exposure to 300 equivalent solar hours UV irradiation and varying doses of 1 MeV electron irradiation. The effects of monomer purity, casting solvent and cure atmosphere on polyimide film transparency are also investigated

Recent developments in polyimide adhesives at NASA-Langley Research Center

Adhesive development is directed towards elevated temperature applications (200-300 C). Because of thermal stability considerations, the most attractive adhesives for this temperature range are linear and addition polyimides. The linear polymide adhesive research encompassed basic structure-property relationships, solvent studies and formulations to meet various requirements. The most recent research in linear polyimide systems was in the development of thermoplastic systems in an effort to eliminate the undesirable evolution of water classically associated with the cure going through an amide-acid intermediate step in the cure process. Addition polyimide adhesive research was undertaken in order to avoid water evolution during cure. Basic structure-property relationships for these materials led to an adhesive which was used extensively for high temperature adhesive needs. Since addition systems are of a highly crosslinked nature, they are not as resistant to impact as their linear counterparts. In order to overcome this problem, research was done in the area of elastomer-toughening these polymers

Process for lowering the dielectric constant of polyimides using diamic acid additives

Linear aromatic polyimides with low dielectric constants are produced by adding a diamic acid additive to the polyamic acid resin formed by the condensation of an aromatic dianhydride with an aromatic diamine. The resulting modified polyimide is a better electrical insulator than state-of-the-art commercially available polyimides

Tough, high performance, addition-type thermoplastic polymers

A tough, high performance polyimide is provided by reacting a triple bond conjugated with an aromatic ring in a bisethynyl compound with the active double bond in a compound containing a double bond activated toward the formation of a Diels-Adler type adduct, especially a bismaleimide, a biscitraconimide, or a benzoquinone, or mixtures thereof. Addition curing of this product produces a high linear polymeric structure and heat treating the highly linear polymeric structure produces a thermally stable aromatic addition-type thermoplastic polyimide, which finds utility in the preparation of molding compounds, adhesive compositions, and polymer matrix composites

Aluminum ion-containing polyimide adhesives

A meta-oriented aromatic diamine is reacted with an aromatic dianhydride and an aluminum compound in the presence of a water or lower alkanol miscible ether solvent to produce an intermediate polyamic acid. The polyamic acid is then converted to the thermally stable, metal ion-filled polyimide by heating in the temperature range of 300 C to produce a flexible, high temperature adhesive

Processing for maximizing the level of crystallinity in linear aromatic polyimides

The process of the present invention includes first treating a polyamide acid (such as LARC-TPI polyamide acid) in an amide-containing solvent (such as N-methyl pyrrolidone) with an aprotic organic base (such as triethylamine), followed by dehydrating with an organic dehydrating agent (such as acetic anhydride). The level of crystallinity in the linear aromatic polyimide so produced is maximized without any degradation in the molecular weight thereof

Methyl substituted polyimides containing carbonyl and ether connecting groups

Polyimides were prepared from the reaction of aromatic dianhydrides with novel aromatic diamines having carbonyl and ether groups connecting aromatic rings containing pendant methyl groups. The methyl substituent polyimides exhibit good solubility and form tough, strong films. Upon exposure to ultraviolet irradiation and/or heat, the methyl substituted polyimides crosslink to become insoluble

Converting water adsorption and capillary condensation in useable forces with simple porous inorganic thin films

This work reports an innovative humidity driven actuation concept based on Bangham effect using simple nanoporous sol-gel silica thin films as humidity responsive materials. Bilayer shaped actuators, consisting on a humidity-sensitive active nanostructured silica film deposited on a polymeric substrate (Kapton) were demonstrated as an original mean to convert water molecule adsorption and capillary condensation in useable mechanical work. Reversible silica surface energy modifications by water adsorption and the energy produced by the rigid silica film contraction, induced by water capillary condensation in mesopores, were finely controlled and used as the energy sources. The influence of the film nanostructure (microporosity, mesoporosity) and thickness, and of the polymeric support thickness, on the actuation force, on the movement speed, and on the amplitude of displacement are clearly evidenced and discussed. We show that the global mechanical response of such silica-based actuators can be easily adjusted to fabricate a humidity variation triggered tailor-made actuation systems. This first insight in hard ceramic stimulus responsive materials may open the door toward new generation of surface chemistry driven actuation systems.Comment: 17 pages, 7 figure