Polyimides thermal stability

Polyimides containing C—F bonds have been receiving strong attention (96—98). Fluorine-containing polyimides possess lower dielectric constant and dielectric loss because of reduced water absorption and lower electronic polarization of C—F bonds vs the corresponding C—H bonds. Fluorine-containing polyimides are often more soluble and readily processible without sacrificing thermal stabilities. The materials are appHed primarily iu... 

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. 

When Tg[(CH2)3NH2]8 reacts with aromatic dianhydrides, it forms hyper-branched polyimide nanocomposite networks having a high thermal stability (up to 500 °C) as shown recently by Se kin et al. (Figure 41). 

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... 

A,A -di(/>-dimethylamino-benzyl) derivatives of di(imidazolidinylidene)gold(i) salts were polymerized into polyimides by condensation with arene-tetracarboxylic anhydrides. The products are tough, but flexible, and have high glass transition temperatures and high thermal stability. Yellow films of the materials are transparent above 365 nm.279... 

N-halamines, 13 100-101 of ion-exchange resins, 14 401-402 of ionic liquids, 26 845-847 of olefin fibers, 11 229 of organic semiconductors, 22 209 of polyimides, 20 277 of silicones, 22 600 of Teflon AF, 18 340 Thermal stability tests, of organic peroxides, 18 491... 

The thermal stability of the polymer is an interesting criterion for one to develop because several authors have considered photoablation as proceeding through a purely thermal degradation. Polyimide and polyphenylquinoxaline, two polymers of the thermostable family, are stable up to a temperature of approximately 500. As seen in Figure 3a, they display quite... 

Aromatic polyimides are well known for their unusual array of favorable physical properties, including excellent thermal stability and excimer-laser processing characteristics. The polyimide structure possesses lower-energy transitions such as n —> n, n —> o, n —> n, and a — n (in order of increasing energy71). However, the w — n and o —> n transitions are forbidden by symmetry rules and related absorptions are significantly weaker than those for... 

Polyimides are high-performance technical polymers mainly used for their short- and long-term thermal stability. 

Thermal stability. The presence of side chains, cross-linking, and benzene rings in the polymer s "backbone increase the melting temperatures. For example, a spectrum of polymers with increasing melting temperatures would be polyethylene, polypropylene, polystyrene, nylon, and polyimide. 

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 ( ). 

The data indicate that the properties of the lower glass transition temperature metal ion modified polyimides are altered more than the properties of the higher glass transition temperature metal ion modified polyimides. Extraction removes both cobalt and chlorine from the films and slightly increases bulk thermal stability and both surface resistivity and bulk electrical resistivity. Details pertaining to the structure, analysis and properties of these novel gradient composites are discussed. 

Each sample was evaluated by thermogravimetry to determine if the thermal stability could be enhanced by removing some residual cobalt chloride. The BTDA-ODA polyimide film thermal stability is reduced about 50 C due to the cobalt chloride dopant. Soa)cing or extraction with water has no positive effect on the thermal stability whereas soxhlett extraction with DMAc severely degrades the polymer stability. For the BDSDA-ODA polyimide films the incorporation of cobalt chloride also reduces the bul)c polymer thermal stability. Soa)cing this film in water for 24 hours, however, increased the bul)c thermal stability slightly from 512 to 532 C. 

One way to cope with this problem is to use polymers that are inherently stable thermally, such as polyimides. A polymer with exceptional thermal stability is the copolymer (5.10), which is made from thermally stable polyimide and chromophore... 

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