Processable polyimides

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). 

The relationships between structures and properties are well documented, and tlte different approaches to get processable polyimides have been discussed in Section 5.2.2. 

The competition at 200°C between an aliphatic and an aromatic amine toward the formation of an imide is a very selective reaction (Fig. 5.1) for the formation of an aliphatic imide.141 This reaction suggests that the reactive processing in extruder, for example, could be used to transform a melt-processable polyimide with an oligomer end capped with an aliphatic amine. In order to get a perfecdy alternate block polyimide-block siloxane, Rogers et al. used low-temperature transimidization.142 An oligomeric aromatic imide was end capped... 

Of especially great interest are processable polyimides e.g., polymers soluble in organic solvents or demonstrating large windows between their softening and degradation temperatures. Usually such polyimides are based on expensive and not easily available monomers such as systems containing... 

Of the various alternatives to design novel processable polyimides, some general approaches have been universally adopted ... 

Since the pioneering works of the Russian researchers, many attempts have been made to prepare new monomers, diamines and dianhydrides, with bulky pendent groups for novel processable polyimides. Table 5 shows some of these monomers. Monomers with small side substituents, like methyl, methoxy, tri-fluoromethyl or halogen, have not been included. In this respect, it is worth noting that many monomers derived from biphenyl, containing small side substituents, have been discovered and used in the synthesis of soluble polyimides in the last few years. They are not going to be discussed in depth in this chapter as they are considered in other parts of this book. 

An easily processable polyimide was prepared by Mercado [2] from the condensation of bisphenol A dianhydride and bis[4-(4-amino-phenoxy)phe-noxyjsulfone that had a Mj, of 76,300 daltons and was used in making thin films. 

In case of ultrafiltration membranes, resistance of membrane is owing to membrane material. Therefore, selection of membrane material is the most important. Figure 9 shows comparison of engineering plastics which have ever investigated for ultrafiltration membranes with solvent and high temperature resistance. It is the most difficult to find materials which satisfy both excellent resistivity and excellent processibility. Polyimide is an only material commercialized for a rather resistant ultrafiltration membrane. 

Deets GL, Xiong J. RTM and RI processable polyimide resins. US patent 7129318, assigned to l.S.T. Corporation, Indian Orchard, MA 2006. 

In an attempt to circumvent the volatile problem. Freeman and coworkers (10) were the first to process polyimides as thermoplastics, above the TgS. Generally,... 

All of these approaches to making processable polyimides reduce several types of polymer interchain interactions, chain packing, and charge transfer electronic polarization interactions or charge transfer complex (CTC) formation. The current chapter presents a comprehensive review focusing on -C(CF3)2-and -CF3-based aromatic polyimides that have been developed between 2000 and 2010, such as low dielectric constant polymers, and well as membrane-based applications such as pervaporation, fuel cell, and gas separation. 

K. Wang, L. Fan, J.-G. Liu, M.-S. Zhan, S.-Y. Yang, Preparation and properties of melt-processable polyimides based on fluorinated aromatic diamines and aromatic dianhydrides, J. Appl. Polym. Sci. 107 (4) (2008) 2126-2135. 

The key to developing a truly melt-processable polyimide was to build more flexible hnkages into the polymer backbone. This had to be done in such a way that the polyimide stiU retained other desirable features (e.g., heat resistance, strength, high use temperatiure, and low flammability). Scientists at the General Electric Corporate Research and... 

An A-B polyimide is also obtained from 4-isocyanatophthalic anhydride (49). Processable polyimides 21 are obtained from the diisocyanate 20 and pyromellitic dianhydride (96). 

Autoclave molding usually involves heat (up to 260°C), pressure (35-50 psi) and vacuum. This method is particularly attractive for processing condensation-type polyimides and some processable polyimides. ... 

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