Aromatic polyamides, See

Both m- and -phenylenediamine react with ben2enedicarbonyl dichlorides to give linear, fully aromatic polyamides (see High performance fibers). 

Unusual properties of fully aromatic polyesters are observed if they have at least partially a rigid planar chain structure. In particular, they can form thermotropic liquid crystalline states (see Example 4-5). As already discussed in Sect. 1.2.4 an important structural prerequisit for LCPs of Type A in order to attain the liquid crystalline state of aromatic polyesters (and aromatic polyamides, see Example 4-14), is a rigid main chain according to the following construction principle ... 

Aramid Fibers. Aromatic polyamide fibers exhibiting a range of mechanical properties are available from several manufacturers, perhaps the best known being Du Pont s proprietary fiber Kevlar. These fibers possess many unique properties, such as high specific tensile strength and modulus (see Fig. 4). Aramid fibers have good chemical resistance to water, hydrocarbons, and solvents. They also show excellent flame retardant characteristics (see High PERFORMANCE fibers Polyamdes). 

The successful development of polyfethylene terephthalate) fibres such as Dacron and Terylene stimulated extensive research into other polymers containing p-phenylene groups in the main chain. This led to not only the now well-established polycarbonates (see Chapter 20) but also to a wide range of other materials. These include the aromatic polyamides (already considered in Chapter 18), the polyphenylene ethers, the polyphenylene sulphides, the polysulphones and a range of linear aromatic polyesters. 

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

Aliphatic iodine derivatives, 14 376 Aliphatic ketones, 14 563, 571, 581-585 reactions of, 16 331-332 Aliphatic monothiopolyesters, 23 739 Aliphatic nitration, 12 187 Aliphatic peroxyacids, 13 464 Aliphatic peroxycarboxylic acids, 18 463 Aliphatic phosphines, 19 60 Aliphatic polyamides (PA), 10 207-210 19 713, 739. See also Aromatic polyamides PA entries producers of, 10 210 properties of, 10 208, 209t Aliphatic polycarbonates, 24 703 preparation of, 19 798 Aliphatic polyketones (PK), 10 197 costs of, 10 222 properties of, 10 198t Aliphatic poly(monosulfide)s, 23 702-704 Aliphatic polyphosphonate dyes, 9 480 Aliphatic poly(polysulfide)s, 23 711 Aliphatic polysulfides, 23 734 Aliphatic polysulfoxides, 23 733 miscibility of, 23 735 Aliphatic polyurea preparation, carbonyl sulfide in, 23 625... 

Aromatic nitrations, 17 160-161 by-products of, 17 161 kinetics of, 17 162 Aromatic nitriles, 17 243 Aromatic nucleophilic displacement, polyimide synthesis via, 20 273 Aromatic phosphines, 19 60, 62 Aromatic poly(monosulfide ketone)s, 23 709 Aromatic poly(monosulfide)s, 23 706 Aromatic polyamide copolymers, laboratory synthesis of, 19 720 Aromatic polyamide fibers, 24 614 Aromatic polyamides, 10 210-212 19 713-738. See also Aliphatic polyamides (PA)... 

Thermal properties. See also Temperature of aromatic polyamides, 19 718 of asbestos, 3 300-304 of diesel fuel, 12 423 of ethylene—tetrafluoroethylene copolymers, 18 319-321 of fibers, 11 167 of filled polymers, 11 309—310 of gallium, 12 342 of glass, 12 588... 

Feast et alJ68-70al reported the convergent construction of a series of aromatic polyamide dendrimers exactly analogous to the amide-based macromolecules described by Miller and NeenanJ3 The synthetic transformations employed for wedge construction were also similar except that reduction of the aromatic nitro group was effected by treatment with NaBFL and SnC -I O instead of catalytic reduction (see Scheme 5.22). 

K. 1971 - Richter-Hoehn at DuPont patents aromatic polyamide membrane (see Chapter 4.2.2)... 

In 1971, E. I. Du Pont De Nemours Company, Inc. (DuPont) patented a linear aromatic polyamide with pendant sulfonic acid groups, which they commercialized as the Permasep B-9 and B-10 membranes (Permasep is a registered trademark of DuPont Company, Inc. Wilmington, DE). These membranes exhibited higher water flux at slightly lower operating pressures than cellulose acetate membranes. The membranes were cast as unique hollow fine fibers rather than in flat sheets or a tubes (see Chapter 4.3.4). 

An example of how ab initio calculations may be applied to the study of fragments of polymer chains is given by Jaffe, Yoon, and McLean, who studied a series of mono- and diphenyl molecules containing up to 35 atoms. These compounds are models for a variety of important polymers such as polycarbonates (see Figure 1), polyimides, aromatic polyamides, aromatic polyesters, and polyether sulfone. A variety of basis sets, representing linear combination of Gaussian functions to approximate Slater-type orbitals (STOs) as compiled in Table 1, were employed. 

The range of polymers which were found to be able to form liquid crystalhne systems has been considerably extended. Poly(Y-benzyl-L-glutamate) and its analogs, as well as para-aromatic polyamides, exhibit this property in solutions, which served the basis for relating them to lyotropic liquid crystals (see Sect. 2.1). Subsequently, the classes of polymers were found which exhibited such a transition during a change of temperature thermotropic liquid crystals). 

For para-aromatic polyamides, the experimental results have also been obtained that confirm the existence of phase transitions from isotropic solutions to anisotropic ones via the region of coexistence of the two phases. This is illustrated by Fig. 5 (see also... 

Fig. 44. [nj/lT l vs. Z plot (Z = relative (xrntent of mete-phenyl rings in the chain) for solutions of some aromatic polyamide in copolymers in sulfuric acid (points indicate experimental data). Curves 1, 2 see text... 

Aliphatic polyamides are extensively studied by natural abundance 15NNMR spectroscopy in solution. However, characterization of polyamides in solution is limited by the insolubility of many (particularly aromatic) polyamides. On the other hand, chemical shifts of amide nitrogens are strongly dependent on the nature of a solvent, and for a particular polyamide, could cover approximately 20 ppm, as in the case of fluorosulfonic acid and trifluoroethanol (see Fig. 2). Since the important properties of solid polyamides such as crystalline structure and hydrogen bonding cannot be studied by solution spectra, the various solid state 15N NMR techniques have been used for structural and dynamical characterization of these polymeric materials. 

Commercial polymers based on the principle of synthesis of polyaromatic compounds include the previously discussed commercial polymers—aromatic polyamides, polyimides, polyfphenylene oxide), polysulfone, and polybenzimidazole (see Chapter 4). 

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