Kevlar, synthesis

Fibers in which the basic chemical units have been formed by chemical synthesis, followed by fiber formation, are called synthetic fibers. Examples include nylon, carbon, boron fibers, organic fibers, ceramic fibers, and metallic fibers. Among all commercially available fibers, Kevlar fibers exhibit high strength and modulus. (Kevlar is a DuPont trademark for poly [p-phenylene diamine terephthalamide].) It is an aromatic polyamide (aramid) in which at least 85% of the... 

The first synthesis of Kevlar by solution polymerization was reported by S. L. Kwolek, P. W. Morgan, and W. R. Gorenson of DuPont in U. S. Patent 3,063,966 (1962). In 1980, Stephanie Kwolek won the American Chemical Society s Award for Creative Invention, and on July 22, 1995, she was inducted into the National Inventors Hall of Fame in Akron, Ohio. In 1996 Stephanie Kwolek was awarded... 

A more recently published example of organic microwave synthesis under CF conditions is the 1,3-dipolar cycloaddition chemistry in the CEM CF Voyager system (Fig. 11). Savin and coworkers presented the cycloaddition of dimethyl acetylene dicarboxylate with benzyl azide in toluene, which was first carefully optimized with respect to solvent, temperature, and time under batch conditions. The best protocol was then translated to a CF procedure where a 0.33 M solution of both building blocks was pumped through a Kevlar-enforced Teflon coil (10 mL total capacity) heated in the single-mode reactor at 110 °C (10 min residence time) [66]. This method provided a 91% conversion to the desired triazole product (Scheme 12). 

Peroxidases belong to the class of oxidoreductases containing iron (111) and protoporphyrin IX as the prosthetic groups. Peroxidases catalyze the reduction of peroxides and the oxidation of many organic and inorganic compounds. These enzymes are widely used for the removal of phenolic compounds, decolorization of synthetic dyes, deodorization of swine manure, in enzyme immunoassays, for biofuel production and organic and polymer synthesis (Hamid and Rehman, 2009). Peroxidases have also been used for the surface modification of poly-p-phenylene-2,6-benzo-bisthiazole (PBO), polyethylene, and grafting of acrylamide onto kevlar fibers. 

The synthesis of step-growth polymers—polytimides such as nylon and Kevlar, polyesters such as Dacron, polyurethanes such as spandex, and polycarbonates such as Lexan (Section 30.6)... 

The most important development in lyotropic liquid crystalline polymers after Kevlar is probably the synthesis of poly [benzo(l,2-d 4,5-d ) bisthiazole-2,6-diyl]-l,4-phenylene, or for short, poly(p-phenylene benzo-bisthiazole) ( PBT Wolfe and Loo, 1980 Wolfe et al., 1981), and the closely related poly [benzo(l,2-d 5,4-d )bisoxazole-2,6-diyl]-l,4-phenylene or poly(p-phenylene benzobisoxazole) ( PBO Helminiak and Arnold, 1977 Wolfe and Arnold, 1981). Both PBT and PBO are lyotropic liquid crystalline and can be spun into fibers with mechanical properties even superior to that of Kevlar fibers. The molecular structures of these polymers are shown in Figure 5.2. 

PET wastes can be converted via ammonolysis to paraphenylenediamine, which is a basic raw material for the high-modulus-fiber Kevlar or for high-value hair dyes. The chemical basis for this process is a modified Hoffman rearrangement. The synthesis may be done via the following three stages [33] ... 

Figure 5 Commercial polyamide polymers, (a) General synthesis and structure, (b) Example of the strong regular hydrogen-bond interactions in Kevlar.

Kevlar is synthesized by the condensation of 1,4-phenylenediamine and terephthaloyl chloride. The synthesis is shown in Figure 13.5. NMP is used as a solvent, together with CaCl2 as an ionic component [15], The process is performed at 0 °C. Before the usefulness of CaCl2 was discovered, a mixture of hexameth-ylphosphoramide and NMP had been proposed [16]. 

Aerogels are quasi-stable, low-density, three-dimensional assemblies of nanoparticles, which have usually poor mechanical properties. A facile one-pot synthesis of Kevlar-like aerogels based on the reaction of multifunctional isocyanates and carboxylic acids has been reported [57]. The materials exhibit an ultimate compressive strength, a high specific energy absorption, and a thermal conductivity like foamed PS. By a pyrolysis process at 800 °C, the materials can be converted to a porous, electrically conducting carbon with a high surface area. 

The same catalyst system was applied for the synthesis of poly(l,3-imino) phenylene ketones, which are isomers of the paro-aramide polymer, known as Kevlar (Scheme 13.63) [112]. 

Bakelite was a thermoset that is, it did not flow after the synthesis was complete (20). The first synthetic thermoplastics, materials that could flow on heating, were poly(vinyl chloride), poly(styrene-5t t-butadiene), polystyrene, and polyamide 66 see Table 1.8 (20). Other breakthrough polymers have included the very high modulus aromatic polyamides, known as Kevlar (see Section 7.4), and a host of high temperature polymers. 

The synthesis of the polyaniline used in this study was reported elsewhere[8,9]. Poly(p-phenylene terephthalamide) with inherent viscosity of 7.43 dl/g was obtained from Du Pont as Kevlar powder. 

One very important chemical activity is the synthesis of new substances. Nylon, the artificial sweetener aspartame (Nutra-Sweet ), Kevlar used in bulletproof vests and the body parts of exotic cars, polyvinyl chloride (PVC) for plastic water pipes. Teflon, Nitinol (the alloy that remembers its shape even after being severely distorted), and so many other materials that make our lives easier—all originated in some chemist s laboratory. Some of the new materials have truly amazing properties such as the plastic that listens and talks, described in the Chemistry in Focus on page 213. When a chemist makes a new substance, the first order of business is to identify it. What is its composition What is its chemical formula ... 

In 1976, the Teijin Co. began with production of a copoly(p-aramide) containing a smaller amount of 4,4 -diamono diphenyl ether in addition to p-pheny-lene diamine. The incorporation of the second diamine slightly reduced the strength of the fiber, but it also had two benefits, first, only one solvent was needed for the synthesis (see below) and second, a patent war with DuPont was avoided. Later Teijin also acquired the Twaron production from the Dutch AKZO. Twaron is the trademark of a Kevlar - like poly(p-aramide) developed by AKZO in the years 1968-1978 [35, 36]. It was commercialized in 1978 under the name Arenka and later renamed. 

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