Films polyimide

VDP Polyimides. Polyimide films have also been prepared by a kind of VDP (16). The poly(amic acid) layer is first formed by the coevaporation and condensation of two monomers, followed by copolymerization on the substrate. The imidization is carried out in a separate baking step (see POLYIMIDES). 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Table 2. Properties of High Temperature Polyimide Films...

Commonly accepted practice restricts the term to plastics that serve engineering purposes and can be processed and reprocessed by injection and extmsion methods. This excludes the so-called specialty plastics, eg, fluorocarbon polymers and infusible film products such as Kapton and Updex polyimide film, and thermosets including phenoHcs, epoxies, urea—formaldehydes, and sdicones, some of which have been termed engineering plastics by other authors (4) (see Elastol rs, synthetic-fluorocarbon elastol rs Eluorine compounds, organic-tdtrafluoroethylenecopolyt rs with ethylene Phenolic resins Epoxy resins Amino resins and plastics). 

Kapton resin (5) (113) and Upilex (6) resin (114) are sold as films, partially polymerized resin coating solutions, and sinterable powders. Allied Signal also offers Apical polyimide film. 

The sizes and concentration of the free-volume cells in a polyimide film can be measured by PALS. The positrons injected into polymeric material combine with electrons to form positroniums. The lifetime (nanoseconds) of the trapped positronium in the film is related to the free-volume radius (few angstroms) and the free-volume fraction in the polyimide can be calculated.136 This technique allows a calculation of the dielectric constant in good agreement with the experimental value.137 An interesting correlation was found between the lifetime of the positronium and the diffusion coefficient of gas in polyimide.138,139 High permeabilities are associated with high intensities and long lifetime for positron annihilation. 

Figure 18. Dynamical optical absorption responses for (a,c) the polyimide film implanted with 5 x 10 Au /cm and for (b,d) the virgin film obtained upon different exposures to (a,b) methanol vapors (6000 ppm) or (c,d) to ethanol vapors (6000 ppm).

Fig. 6.13. The kinetics of bending of polyimide film with deposited silver (/) and emission of O-atoms (2) when oxygen is let inside the vial.

A polyimide film was made by heating a polyamide carboxylic acid at 300 °C for 30 min with azolides such as iV-acetylimidazole, iV-trifluoroacetylimidazole, or N-benzoy limidazole.[ 1633... 

The use of specialty substrates for labels have been driven by the market looking for materials with greater dimensional stability at higher temperature, improved mechanical performance under harsh environments, and resistance to scratching and tearing. Up until now, PET-based labels have been used where conditions are moderate, while polyimide-based labels have been employed in the most extreme environments. PEN films offer a unique performance advantage over PET and a considerable cost saving when compared to polyimide films. 

A representative sample of many of the polyimide films that were produced were subjected to thermo-mechanical analysis (TMA), torsional braid analysis (TBA), thermal gravimetric analysis (TGA), infrared spectral analysis and weight loss on prolonged heating (e.g. isothermal studies), TABLE II. The softening temperature as measured by TMA and TBA are in general... 

The residual thermal stress was investigated with a Plexus stress analyzer. The residual stress, was calculated from the radii of wafer curvatures before and after polyimide film deposition by the following equation ... 

Rothman (52) investigated the planarization of polyimide films over features tens of micrometers in size and separation. Bassous and Pepper (55) studied planarization of PMMA and AZ1350J over features pertinent to Si wafer processing. A mechanical stylus was used to determine the topography of the wafer and the corresponding surface variation of the resist thickness as shown in Figure 29 where a 1.7 - pm thick AZ1350J layer was spun on steps of different space and width combinations. 

As stated, the capability of plasma deposits to reduce the access of water to corrosion-sensitive surfaces may be an important motivation for their application in corrosion protection. In order to study this property, Kapton polyimide film was selected as the substrate because of its high inherent permeability to water and its ability to resist elevated temperatures. The response of Kapton film overcoated by PPHMDSO to the permeation of water vapor is shown in Fig. 1. Clearly, the presence of the organo-silicone plasma film greatly reduces water permeation. The magnitude of the effect is much enhanced when plasma polymers are produced at high T and p. 

Cobalt(II) chloride was dissolved in poly(amide acid)/ N,N-dimethylacetamide solutions. Solvent cast films were prepared and subsequently dried and cured in static air, forced air or inert gas ovens with controlled humidity. The resulting structures contain a near surface gradient of cobalt oxide and also residual cobalt(II) chloride dispersed throughout the bul)c of the film. Two properties of these films, surface resistivity and bullc thermal stability, are substantially reduced compared with the nonmodified condensation polyimide films. In an attempt to recover the high thermal stability characteristic of polyimide films but retain the decreased surface resistivity solvent extraction of the thermally imidized films has been pursued. 

Metal ion modified polyimide films have been prepared to obtain materials having mechanical, electrical, optical, adhesive, and surface chemical properties different from nonmodified polyimide films. For example, the tensile modulus of metal ion modified polyimide films was increased (both at room temperature and 200 0 whereas elongation was reduced compared with the nonmodif ied polyimide (i). Although certain polyimides are )cnown to be excellent adhesives 2) lap shear strength (between titanium adherends) at elevated temperature (275 0 was increased by incorporation of tris(acetylacetonato)aluminum(III) (2). Highly conductive, reflective polyimide films containing a palladium metal surface were prepared and characterized ( ). The thermal stability of these films was reduced about 200 C, but they were useful as novel metal-filled electrodes ( ). 

Extraction of Films. Cobalt modified polyimide films were extracted by one of several techniques (1) films on the casting plate were soaked in a tray of distilled water at room temperature, (2) films were soxhlett extracted with distilled water, (3) films were soaked in DMAc at room temperature, and (4) films were soxhlett extracted with DMAc. 

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