Polyimide, properties thermal

Polyimide-clay nanocomposites constitute another example of the synthesis of nanocomposite from polymer solution [70-76]. Polyimide-clay nanocomposite films were produced via polymerization of 4,4 -diaminodiphenyl ether and pyromellitic dianhydride in dimethylacetamide (DMAC) solvent, followed by mixing of the poly(amic acid) solution with organoclay dispersed in DMAC. Synthetic mica and MMT produced primarily exfoliated nanocomposites, while saponite and hectorite led to only monolayer intercalation in the clay galleries [71]. Dramatic improvements in barrier properties, thermal stability, and modulus were observed for these nanocomposites. Polyimide-clay nanocomposites containing only a small fraction of clay exhibited a several-fold reduction in the... 

Polyimides are thermally stable, heterocyclic aromatic materials of desirable engineering properties. They are, however, insoluble. A typical mode of preparation1 18 11is given in Fig. 29 where reactants (a) as well as the polyamic acid or pyrrone prepolymers (b) are maintained in solution. 

Polymer properties are highly sensitive to temperature with transitions between physical states typically occurring over many tens of degrees Celsius (A). Additionally, the properties are sensitive to the rate at which the temperature changes. For example, the apparent glass transition temperature of a given polymer sample increases with the rate of temperature scan. For thermosets (such as epoxies and polyimides) the thermal history is especially important because of its coupled effect on the physical state of the polymer and the reaction kinetics (11). 

Bending beam theory calculation of elastic modulus, 361-362 calculation of glass temperature, 362 calculation of thermal expansion coefficient, 362 layer stress determination, 361 Benzophenone-3,3, 4,4 -tetracarboxydi-anhydride-oxydianiline-m-phenylenediamine (BTDA-ODA-MPDA) polyimide, properties, 115-116 Bilayer beam analysis schematic representation of apparatus, 346,348/ thermal stress, 346 Binary mixtures of polyamic acids curing, 116-124 exchange reactions, 115 Bis(benzocyclobutenes) heat evolved during polymerization vs. 

Sulfonated aromatic polymers have been widely studied as alternatives to Nafion due to potentially attractive mechanical properties, thermal and chemical stability, and commercial availability of the base aromatic polymers. Aromatic polymers studied in fuel cell apphcations include sulfonated poly(p-phenylene)s, sulfonated polysulfones, sulfonated poly(ether ether ke-tone)s (SPEEKs), sulfonated polyimides (SPIs), sulfonated polyphosphazenes, and sulfonated polybenzimidazoles. Representative chemical structures of sulfonated aromatic polymers are shown in Scheme 3. Aromatic polymers are readily sulfonated using concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, or sulfur trioxide. Post-sulfonation reactions suffer from a lack of control over the degree and location of functionalization, and the... 

PBO membranes prepared by the thermal rearrangement of the hydroxyl-containing polyimides or polyamides at elevated temperature were used for membrane-based gas separation. Lee s group has done considerable work on the thermally rearranged (TR) PBO membrane (TR-PBO) (Figure 5.38) for gas separation [67,80]. They had studied the effect of imidization methods on the properties of TR-PBO membranes. The final properties of the TR-PBO membranes depended on the synthetic methods to prepare polyimide precursors. There are three different routes for the synthesis of the polyimides (1) thermal, (2) chemical, and (3) solution thermal imidization using an azeotrope. They demonstrated the effect of these routes on the final properties of the PBOs. The precursor ort/jo-functional polyimides were synthesized from 4,4 -hexafiuoroisopropyli-dene diphthalic anhydrides and 2,2 -bis(3-amino-4-hydroxyphenyl)hexafiuoropropane. 

Whilst their molecular structure gives polyimides outstanding thermal properties, under certain conditions some degradation may still occur. At temperatures below 300°C, polyimides are susceptible mainly to hydrolytic types of reaction, whilst above 300°C in air the material decomposes by a free radical initiated oxidation process. In inert atmospheres at high temperatures, pyrolysis occurs yielding carbon monoxide and carbon dioxide as the major decomposition products. The nature of any substrate materials (particularly metals) in contact with a polyimide may have a profound influence on the decomposition rate. 

Polyimide films are used in a variety of interconnect and packaging applications including passivation layers and stress buffers on integrated circuits and interlayer dielectrics in high density thin film interconnects on multi-chip modules and in flexible printed circuit boards. Performance differences between poly-imides are often discussed solely in terms of differences in chemistry, wiAout reference to the anisotropic nature of these films. Many of the polyimide properties important to the microelectronics industry are influenced not only by the polymer chemistry but also by the orientation and structure. Properties such as the linear coefficient of thermal expansion (CTE), dielectric constant, modulus, strength, elongation, stress and thermal conductivity are affected by molecular orientation. To a lesser extent, these properties as well as properties such as density and volumetric CTE are also influenced by crystdlinity (molecular ordering). 

Aromatic polyimides have found wide application in the microelectronics industry as alpha particle protection, passivation, and intermetallic dielectric layers, owing to their excellent thermal stability, mechanical properties and dielectric properties (7-5). Many microelectronic devices, such as VLSI semiconductor chips and advanced multi-chip modules (5), are composed of multilayer structures. In multilayered structures, one of the serious concerns related to reliability is residual stress caused by thermal and loading histories generated through processing and use, since polyimides have different properties (i.e., mechanical properties, thermal expansion coefficient, and phase transition temperature) from the metal conductors and substrates (ceramic, silicon, and plastic) com-... 

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. 

Du Pont produces this polymer under the trade names of Kapton, Pyrafin, Vespel, and Pyre-ML. The trade names refer to polyimides used for film, semiconductor coatings, mol ding applications, and wire enamel, respectively. They have exceUent thermal, electrical, and physical properties. 

Relatively few processible polyimides, particularly at a reasonable cost and iu rehable supply, are available commercially. Users of polyimides may have to produce iutractable polyimides by themselves in situ according to methods discussed earlier, or synthesize polyimides of unique compositions iu order to meet property requirements such as thermal and thermoxidative stabilities, mechanical and electrical properties, physical properties such as glass-transition temperature, crystalline melting temperature, density, solubility, optical properties, etc. It is, therefore, essential to thoroughly understand the stmcture—property relationships of polyimide systems, and excellent review articles are available (1—5,92). 

Phthalazinone, 355 synthesis of, 356 Phthalic anhydride, 101 Phthalic anhydride-glycerol reaction, 19 Physical properties. See also Barrier properties Dielectric properties Mechanical properties Molecular weight Optical properties Structure-property relationships Thermal properties of aliphatic polyesters, 40-44 of aromatic-aliphatic polyesters, 44-47 of aromatic polyesters, 47-53 of aromatic polymers, 273-274 of epoxy-phenol networks, 413-416 molecular weight and, 3 of PBT, PEN, and PTT, 44-46 of polyester-ether thermoplastic elastomers, 54 of polyesters, 32-60 of polyimides, 273-287 of polymers, 3... 

More recently, St. Clair and co-workers176) reported the use of aromatic amine terminated polydimethylsiloxane oligomers of varying molecular weights in an effort to optimize the properties of LARC-13 polyimides. They observed the formation of two phase morphologies with low (—119 to —113 °C) and high (293 to 318 °C) temperature Tg s due to siloxane and polyimide phases respectively. The copolymers were reported to have improved adhesive strengths and better thermal stabilities due to the incorporation of siloxanes. 

PI nanocomposites have been prepared by various methods with different fillers. The nanocomposites might have many applications starting from barrier and thermal resistance to a compound with low coefficient of thermal expansion (CTE) [154-167]. These hybrid materials show very high thermal and flame retardation as well as barrier resistance and adhesion. Tyan et al. [158] have shown that depending on the structure of the polyimide the properties vary. Chang et al. [159] have also investigated the dependency of the properties on the clay modifiers. 

However, fluorocarbon compounds might be of considerable interest for LB-layer fabrication. Their dielectric and mechanical characteristics and thermal and chemical stability are not inferior to those of polyimides, and highly developed synthesis technology makes it possible to create systems with various predictable properties. Such films have been found to demonstrate a high degree of perfection and excellent dielectric characteristics.69,70... 

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