Polymer polyimide materials

Polymer-matrix materials include a wide range of specific materials. Perhaps the most commonly used polymer is epoxy. Other polymers include vinyl ester and polyester. Polymers can be either of the thermoset type, where cross-linking of polymer chains is irreversible, or of the thermoplastic type, where cross-linking does not take place but the matrix only hardens and can be softened and hardened repeatedly. For example, thermoplastics can be heated and reheated, as is essential to any injection-molding process. In contrast, thermosets do not melt upon reheating, so they cannot be injection molded. Polyimides have a higher temperature limit than epoxies (650°F versus 250°F or 350°F) (343°C versus 121°C or 177°C), but are much more brittle and considerably harder to process. 

Like most aromatic polymers, polyimide(fig. 1) absorbs strongly UV radiation in the wavelength region below 200 nm (absorption coefficient a =4.10 cm-l) (ILL. Therefore, the penetration depth of the UV light in this material is very small about two thirds of the radiation intensity is absorbed in the first 300 A of the polyimide film. 

The bonding of metals onto polymer surfaces has received considerable attention these last few years, especially with polyimide materials. Interfacial reactions are quite dependent on the nature of the metallic deposit. For instance Ag (1), Cu (2-3) and Pd (4) do not react with polyimide while Cr (1, 3-5), Ni (1) and Ti (6) do easily react. 

Swift heavy ion beams with extremely high LETs are used to degrade strongly polymer chains within tracks over a range of a few tens of micrometers. After irradiation, the top surface of bulk thermoplastics such as polyethyleneterephtalate, polycarbonate, polyvinylidene fluoride or polyimide materials as well as thin films made of the same material are subsequently etched by a wet chemical treatment that reveals pores of which the shape, surface density and dimensions can be controlled by choosing appropriate conditions. High aspect ratio cylindrical or conical traces of diameter ranging from a few nanometers to some... 

PANI has been doped with poly(amic acid) in order to obtain an all-polymer conducting material, by Angelo-poulos el a . [337]. Its structure has not been investigated, but the authors present x-ray diffraction results for cured specimens, in which polyimide formation has taken place at the expense of the carboxylic acid groups. The diffraction is structureless there is no indication that the elimination of the ionic interaction leads to phase separation of the polymers. 

Polyimide materials can be used as unfilled base polymers or have graphite, PTFE and molybdenum disulphide added to further enhance the low frictional properties and can be used to replace metal and ceramic parts. Material is available as moulded stock shapes, e.g. rod, rings and plate, which can be machined to the final dimensionally accurate product. Some grades can be processed by compression moulding while other grades can be processed to produce a finished product by direct forming. 

On the one hand, linear aromatic polyimides have been generally used as electronic and aerospace materials because of their excellent mechanical strength, thermal, chemical and electronic/optic properties compared with other common amorphous polymers. Polyimides are also excellent membrane materials for gas separation due to their rigid chemical structures, allowing the production of larger functional free volume. Over the... 

In addition to conventional materials engineering polymers include materials as diverse as polyether ether ketone, polyimide, polyetherimide and polysulfides. 

Solvent-Soluble Polyimides. Materials in this class are also termed preimidized polyimides because the film-forming polymer is a polyimide rather than a polyimide precursor such as a polyamic acid. Thus, the curing process for these materials involves only removal of solvent. In some instances, a high... 

To obtain good initial alignment, varieties of polyimide materials for the alignment layer were investigated.The mmetry of the polymer molecules is critically important. In Table 6.2.1 [11], the molecular structures of polyimide materials, the evaluation of the alignment state and the contrast ratios of AFLCDs using the polyimides are shown. 

Fig. 19.1 The plastics pyramid according to thermal literature data of common polymers preferred materials for HT-PEM applications are in the upper right region TPI thermoplastic polyimide, PES polyether sulfone, P P)SU poly(phenylene)sulfone, PE E)K polyether(ether) ketone, LCP liquid crystal polymer, e.g., Vectra, PPS polyphenylene sulfide, PTEE polytetrafluoroethylene.

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