Polypyromellitimides

Uses. Pyromellitic dianhydride imparts heat stabUity in applications where it is used. Its relatively high price limits its use to these applications. The principal commercial use is as a raw material for polyimide resins (see POLYIMIDES). These polypyromellitimides are condensation polymers of the dianhydride and aromatic diamines such as 4, -oxydianifine ... 

The first commercial applications of polypyromellitimides were as wire enamels, as insulating varnishes and for coating glass-cloth (Pyre.ML, Du Pont). In film form (Kapton) many of the outstanding properties of the polymer may be more fully utilised. These include excellent electrical properties, solvent resistance, flame resistance, outstanding abrasion resistance and exceptional heat resistance. After 1000 hours exposure to air at 300°C the polymer retained 90% of its tensile strength. 

Photoconductivity of Kapton, (polypyromellitimide where R is oxygen) was investigated in detail [224-234]. Frenkel, Onsager, hopping and other models were used by different authors for explanation of the photoconductive properties. The photoconductivity spectra of Kapton film for various directions of the electric field are presented in Fig. 29 [230]. The high anisotropy depending on... 

To improve the solubility of polyimides, Korshak and co-workers used l,l-dichloro-2,2-bis(4-aminophenyl)-ethylene as the starting nucleophile [17] (Scheme 3.2). The resulting polymers turned out to be of relatively high molecular weight (r = 1.2-1.4 dl/g), heat resistant > 270 °C) and fire resistant (oxygen index (OI) = 36-39) (Table 3.2). Polypyromellitimide was soluble in H2SO4 only, but polyimides based on the dianhydrides of benzophenone-3,3, 4,4 -tetracarboxylic acid and diphenyloxide-3,3, 4,4 -tetracarboxylic acid were also soluble in w-cresol and a trichloroethane (TCE)/phenol (3 1) mixture. Diphenyloxide-3,3, 4,4 -tetracarboxylic acid was soluble even in N-methyl-2-pyrrolidone (NMP) (Scheme 3.2). 

For thermal stability polypyromellitimides are somewhat inferior to polyimides based on the anhydrides of other aromatic tetracarboxylic acids. This is apparently due to the higher chlorine content per unit polymer weight in the former. 

The effect of aromatic diamine residues on the heat resistance of polyimides is less clear cut. It was only by comparing thermomechanical curves of polypyromellitimides obtained from 3,3-diamino-4,4 -dichlorodiphenylmethane, and l,l-dichloro-2,2-di(3-amino-4-chlorophenyl)-ethylene that the system containing the 1,1-dichloroethylene group was found to be less heat resistant. With polyimides prepared from other dianhydrides this rule holds true as well but is less distinct. 

On passing from polyimides constructed from l,l-dichloro-2,2-di(p-aminophenyl)-ethylene to systems prepared from 3,3 -diamino-4,4 -dichlorobenzophenone and 3,3 -diamino-4,4 -dichlorodiphenylmethane, solubility somewhat decreases. The resulting polypyromellitimides are insoluble in phenolic solvents and chloroform, while they remain soluble in NMP. 

Polyimides based on l-amino-3-phenoxy-5-(4-aminophenoxy)-benzene and snch dianhydrides as dianhydride of diphenyloxide-3,3 4,4 -tetracarboxylic acid, dianhydride A and dianhydride 6F are soluble in NMP, dimethylformamide (DMF), w-cresol, THF and chloroform. The polyimide based on benzophenone-3,3, 4,4 -tetracarboxylic acid dianhydride is partially soluble in w-cresol and NMP it is insoluble in chloroform, THF and DMF. Polypyromellitimide is insoluble in all the solvents tested. 

Polypyromellitimide films based on cyclotriphosphazene and bisaspartimide-derived diamines have shown thermal stabilities up to 800°C and char yields of 56—68% in N2 and 24% in air (29). High strength fire- and heat-resistant imide resins containing cyclotriphosphazene and... 

We might expect catalytic action by materials containing paramagnetic centres, and interesting correlations have indeed been found between the electromagnetic properties of organic polymers and their catalytic activity for this reaction103 1061. Two classes of polymers were studied, the polypyromellitimides,... 

Hie polyimides made from aromatic diamines are more stable but the decreased flexibility of an aromatic ring raises the glass transition temperature (Tg) of the polymer quite significantly, and no Tg can be measured for, say, the polyimide based on phenylene diamine. Thus flexibilizing units must be introduced, but these tend to raise the price of the diamine, and decrease the temperature stability. A compromise must be reached, and the best known polypyromellitimide is Kapton/Vespel made by du Pont this is based on oxydianiline. 

Example 2.3 Polyimides have been prepared from aromatic anhydrides and aliphatic diamines by melt fusion of salt from the diamine and tetracid (dianhydride). Ahphatic polypyromellitimide derived from straight-chain aliphatic diamines containing more than nine carbon atoms gave thin, flexible films, whereas those from shorter chain aliphatic diamines allowed the preparation of only thick, brittle moldings. Explain this observation. 

Thermo-oxidative Degradation of Polypyromellitimide, Poly(phenyl-quinoxaline) and Copoly(imidophenylquinoxalines) [1-11]... 

The aromatic polyimide (PI) of Fig. 3.49 is a relatively stable polymer, such as a polypyromellitimide, that is usable for high-temperature applications such as needed for insulation. It finally decomposes to small fragments that carry away most H-atoms and leave highly cross-linked, high-carbon chars. 

Polyimides (Pis) represent a broad class of high-Jg polymers derived from the polycondensation of an aromatic dianhydride and diamine. The most widely investigated polyimide is polypyromellitimide or poly(4,4 -oxydipheny-lenepyromellitimide) (Kapton ) whose repeat tmit structure is given below... 

PI, polypyromellitimide (Kapton polyimide) or poly(4,4 -oxydiphenylenepyromellitimide) PEI, poly(ether-imide) PAI, poly-... 

Vespel-SP Polyimide (polypyromellitimide) electrical parts E. I. du Pont de Nemours... 

Polypyromellitimide (PPM) n. The original polyimide family of polymers, having enhanced heat resistance and formed from polyamide carboxylic acids derived by reacting pyromellitic dianhydride with 4,4 -diaminophenyl ether. Grades of the polymer are used for forming films, paint components, and are processable as thermoplastics under special conditions. More easily processed co-polymers have enjoyed greater commercial success. 

The conductivity of metallopolymeric nanocomposites is substantially affected by the dispersity of an inorganic component. Different nanocomposites are characterized by different relationships between the conductivity and the metal content. The percolation threshold of composites containing layered polypyromellitimide films filled by inserted silver particles is attained at a filler content >9 wt%. When nanosize silver particles (10-15 nm), were prepared by thermolysis of a solution of silver acetate in poly(pyromellitamide acid), they became uniformly distributed over a film. This composite does not exibit conducting properties at the same filler content. The dielectric characteristics of films (o = 10 - 10 Sm ) are retained at a high... 

Bruck, S. D., Thermal degradation of aromatic polypyromellitimide in air and vacuum. III. Pyrolytic conversion into a semiconductor. Polymer, 6, 319-332 (1965). 

The basic chemistry of aromafic polyimides was first disclosed in patents filed by Du Pont de Nemours [5] for polypyromellitimides and later on by Edwards [6, 7] for polyimides prepared with various aromatic dianhydrides and diamines. They compose... 

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