High temperature adhesives other polymers

Polyphenylquinoxalines (PPQ s) were first prepared in 1967 by Hergenrother (56). In 1975, Koval et al. (57,58) introduced the acetylene-terminated PPQ (ATPQ) (Pig. 10), which is the addition type of PPQ. Resembling ATPI, ATPQ also has shortcomings. The ethynl group hinders the flow of the polymer chain, and the cured ATPQ is less thermal-oxidatively stable than the comparable PPQ. The detailed status of PPQ, as well as other high-temperature adhesives, is discussed by Hergenrother (45). ... 

To achieve maximum adhesive properties at the higher temperatures (e.g. 538 0 PBI like other high temperature adhesives, must be postcured. The final postcure temperature depends upon the maximum use temperature. Postcure temperatures as high as 454 C have been employed. The high temperature postcure induces cross-linking in the polymer which is generally reflected in lower room temperature TSS (more brittle) but improved short term performance at elevated temperatures. A PBI similar to Imidite 850 is available in experimental quantities and is still under evaluation as an adhesive (4). ... 

There are several other classes of polymers being examined for high-temperature adhesive and composite applications, such as phthalo-cyanines, " aromatic nitriles,polytriazines, ladder polymers such as poly-bis(benzimidazophenanthroline) (BBP polymers), " and polyphenylene." Many of these materials are not commercially available and much more work is needed before successful applications will be found. 

Future developments will undoubtedly attempt to correct these deficiencies, so that high-temperature adhesives may become an attractive alternative to other joining methods. The introduction of addition-type polymers has gone some way toward improving and making the bonding of large areas feasible new cure chemistries could offer further improvements. The adhesive systems evaluated to date have all relied on the application of... 

Much attention has been paid to the synthesis of fluorine-containing condensation polymers because of their unique properties (43) and different classes of polymers including polyethers, polyesters, polycarbonates, polyamides, polyurethanes, polyimides, polybenzimidazoles, and epoxy prepolymers containing pendent or backbone-incorporated bis-trifluoromethyl groups have been developed. These polymers exhibit promise as film formers, gas separation membranes, seals, soluble polymers, coatings, adhesives, and in other high temperature applications (103,104). Such polymers show increased solubility, glass-transition temperature, flame resistance, thermal stability, oxidation and environmental stability, decreased color, crystallinity, dielectric constant, and water absorption. 

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