Soluble polyimide

Both polyimide and epoxy possess a number of unusually valuable characteristics that make them amenable for use in a vast array of applications. Until quite recently, however, the two compounds have not been concurrently fabricated into a material that combines their desirable properties. Recently advances in polyimide solubility and have made the fabrication of polyimide-epoxy composites possible. This chapter reports the various fabrication strategies and problems encountered in synthesis and characterization of the formed composites and opens up the possibility of further endeavor in this field of research. 

The purpose of this investigation was to observe the effects on solubility of changing isomeric points of attachment of phenoxy units in the diamine portion of several all-aromatic polyimide systems. Hexafluoropropane- and oxygen-containing dianhydrides were used in this study because of their known value at contributing to polyimide solubility.(6-7)... 

S.A. Sydlik, Z. Chen, T.M. Swager, Tripty-cene polyimides soluble polymers with high thermal stability and low refractive indices. Macromolecules 44 (4) (2011) 976-980. 

As the introduction of asymmetric bulky groups was the method to improve the solubility of the polyimides, soluble polyimides with norbornene [58], phenylphthalide [59], and adamantine moieties [60] were prepared (Figure 7.20). 

Polyimides for use ia molded products and high temperature films can be produced by the reaction of pyromelHtic dianhydride [89-32-7] and 4,4 -diaminodiphenyl ether [13174-32-8] ia DMAC to form a polyamide that can be converted iato a polyimide (13). DMAC can also be used as a spinning solvent for polyimides. AdditionaUy, polymers containing over 50% vinyHdene chloride are soluble up to 20% at elevated temperatures ia DMAC. Such solutions are useful ia preparing fibers (14). 

Synthesis and Properties. Several methods have been suggested to synthesize polyimides. The predominant one involves a two-step condensation reaction between aromatic diamines and aromatic dianhydrides in polar aprotic solvents (2,3). In the first step, a soluble, linear poly(amic acid) results, which in the second step undergoes cyclodehydration, leading to an insoluble and infusible PL Overall yields are generally only 70—80%. 

Diesters of Tetracarboxylic Acids with Diamines. Dianhydrides react with alcohols at a moderate temperature, producing the tetracarboxyhc acid diesters. Ben2ophenonetetracarboxyhc acid diester (BTTA diester) is obtained from B I DA as a mixture of three positional isomers. Partiy because it is an isomeric mixture, the diester of BTTA is soluble in methanol at high concentrations. A state-of-the-art thermoset polyimide,... 

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). 

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... 

The reaction product of 4,4 -bismaleimidodiphenylmethane and 4,4 -diaminophenylmethane, known as Kerimide 601 [9063-71-2] is prepolymerized to such an extent that the resulting prepolymer is soluble in aprotic solvents such as /V-methy1pyrro1idinone [872-50-4] dimethylformamide [68-12-2] and the like, and therefore can be processed via solution techniques to prepreg. Kerim ide 601 is mainly used in glass fabric laminates for electrical appHcations and became the industry standard for polyimide-based printed circuit boards (32). 

For convenience of application it is usual to utilise the two-stage preparation shown above. Initially the soluble polymer (I) is formed which is then converted into the insoluble thermally stable polyimide (II) Figure 18.35). Suitable solvents for the high molecular weight prepolymer (I) include dimethylformamide and dimethylacetamide. 

Basically, the first approach to correlate the polyimide chain organization to the monomer structure was to take into consideration the electron affinity of the anhydride and the ionization potential of the diamine,10 as shown in Fig. 5.3. The strongest interactions between the polymeric chain are expected when the polyimide is prepared with the dianhydride having the highest electron affinity and die diamine with the lowest ionization potential. The strongest interchain interaction leads to high Tg and low solubility. 

Figure 5.5 Bulky substituents used for preparation of soluble high-Tg polyimides.

This method is being increasingly used for the preparation of soluble polyimides, and the rate is faster than in aprotic solvents. This method allows for preparation of block copolyimides.78... 

Optical properties, of colorless polyimides, 277-279 Optical rotation, 490 Opto-electronic targets, 271-272 Organic phase-soluble aromatic polyesters, 77... 

Solid-state synthesis, of polyimides, 304 Solid stating technology, 530 Solid waste disposal, 27 Solubility, 3... 

Acetylene terminated polyimide prepolymers have many advantages over conventional polyimides in the areas of processing and solvent resistance. In addition, the presence of the isoimide structure further extends the the utility of these systems by modification of the solubility properties and glass transition temperature. 

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