Nylon chemical structure

The family of polymers that we refer to as nylons consists of molecules composed of amide groups alternating with short runs of methylene units. These molecules are also known as polyamides, which may be shortened to PA. The generic chemical structure of a nylon molecule is shown in Fig. 23.1. Variations on this basic structure include the length of the polymethylene sequences and the orientation of the amide groups relative to their neighbors. Figure 23.2 shows the chemical structures of nylon 6 and nylon 66, which are the two most common types of nylon. 

Figure 23.1 Generic chemical structure of a nylon molecule...

Other commercially important polyamides include nylon 11, nylon 12, nylon 46, nylon 610 ( nylon six ten ) and nylon 612 ( nylon six twelve ), the chemical structures of which are shown in Fig. 23.5. 

Figure 23.5 Chemical structure of repeat units of various commercial nylons a) nylon 11,b) nylon 12,c) nylon 46, d) nylon 610, and e) nylon 612...

Nylon (polyamide fibers). The chemical structure of the nylon fiber looks just like the nylon resin. The polymerization processes are the same the numbering systems are the same and the two most important nylon fibers are the same nylon, 6 and 66. The difference is the length of the molecule in comparison to the cross-section. Thats regulated by the polymerization process conditions. 

Nylon-6,6 and nylon-6 have competed successfully in the marketplace since their respective commercial introductions in 1939 and 1941, and in the 1990s share, about equally, 90% of the total polyamide market. Their chemical and physical properties are almost identical, as the similarity of their chemical structure might suggest the amide functions are oriented in the same direction along the polymer chain for nylon-6, but are alternating in direction for nylon-6,6. 

Dyeing Mechanism. Nylon i.s. similar in its general chemical structure to the natural fiber wool, and therefore all the previously described processes lor wool are applicable to dyeing nylon with acid, metallized, and other dyes. There are. however, significant differences. Nylon is synthetic, it has delined chemical structure depending on the manufacturing process, and it is hydrophobic. 

Reactive Dyes. These dyes form a covalent bond with the fiber, usually cotton, although they are used to a small extent on wool and nylon. This class of dyes, first introduced commercially in 1956 by ICI, made it possible to achieve extremely high washfastness properties by relatively simple dyeing methods. A marked advantage of reactive dyes over direct dyes is that their chemical structures are much simpler, their absorption spectra show narrower absorption bands, and the dyeings are brighter. The principal chemical classes of reactive dyes are azo (including metallized azo), triphendioxazine, phthalocyanine, formazan, and anthraquinone (see Section 3.1). 

The manufacture of the large variety of polyamides (commonly referred to as nylons) occurs through polycondensation of amino carboxylic acids (or functional derivatives of them, e.g. lactams) and from diamines and dicarboxylic acids. Labeling the amino groups with A and the carboxyl groups with B allows differentiation of the different chemical structures between the two types AB (from amino carboxylic acids) and AA-BB (from diamines and dicarboxylic acids). The number of C atoms in the monomers acts as a code number for the identification of the polyamides. The polycaprolactam manufactured from caprolactam (type AB) is then called polyamide 6 (PA 6). The number of carbon atoms in the diamine is given first for type AA-BB followed by the number of atoms in the dicarboxylic acid, e.g. PA 66 for polyhexamethylenedia-dipic amide from hexamethylenediamine and adipic acid. For copolymers the components are separated by a slash, e.g. PA 66/6 (90 10) is a copolymer composed of 90 parts PA 66 and 10 parts PA 6. 

Figure 25 shows the 13C CPM AS NMR spectrum of SGC nylon 46 together with the chemical structure. There are five chemically non-equivalent carbons in nylon 46. The carbonyl carbon peak appears at 173 ppm. Four methylene carbons, aB, aa, / B and (ja, correspond to 42, 36, 27 and 26 ppm, respectively.70... 

In much the same way, natural polymeric fibers like wool, cotton, silk, etc., are often touted as superior to anything that is man-made or synthetic. But is this fair There is no doubt that natural fibers have a unique set of properties that have withstood the test of time (e.g., it is difficult, but not impossible, to match silk s feel or cotton s ability to breathe ). On the other hand, consider Lycra , a completely synthetic fiber produced by DuPont (Figure 1-12) that has a truly amazing set of properties and is the major component of Spandex (a material that keeps string bikinis on ). Or consider the wrinkle-free polyester fibers used in clothing and the stain proof nylon and polyacrylonitrile polymers used in carpets. The point here is that polymers, be they natural" or synthetic, are all macromolecules but with different chemical structures. The challenge is to design polymers that have specific properties that can benefit mankind. 

The chemical structure of a polymer determines whether it will be crystalline or amorphous in the solid state. Both tacticity (i.e., syndio-tactic or isotactic) and geometric isomerism (i.e., trans configuration) favor crystallinity. In general, tactic polymers with their more stereoregular chain structure are more likely to be crystalline than their atactic counterparts. For example, isotactic polypropylene is crystalline, whereas commercial-grade atactic polypropylene is amorphous. Also, cis-pol3nsoprene is amorphous, whereas the more easily packed rans-poly-isoprene is crystalline. In addition to symmetrical chain structures that allow close packing of polymer molecules into crystalline lamellae, specific interactions between chains that favor molecular orientation, favor crystallinity. For example, crystallinity in nylon is enhanced because of... 

Natural silk has a high value of 7 x 10 spins/cm. From these data it is clear that very similar amounts of molecular fracture can be obtained in polymers with widely different chemical structures, values approaching 10 spins/g being recorded for CIS PI, CIS PBD, nylon 6 and natural silk under appropriate conditions. Secondly, the lower values obtained for other polymers seem to relate more to their morfdiolo-gy or state rather than their chemical structure e.g. the very low figures for glassy polymers). 

Fig. 1. Chemical structures of barrier polymers, (a) Vinylidene chloride copolymers (b) hydrolyzed ethylene—vinyl acetate (EVOH) (c) acrylonitrile barrier polymers (d) nylon-6 (e) nylon-6,6 (f) amorphous nylon (Selar PA 3426), y = x + 2 (g) nylon-MXD6 (h) poly(ethylene terephthalate) and (i) poly(vinyl...

Nylon is a crystalline polymer with high strength, modulus, and impact resistance. The general chemical structure of Nylon is as follows ... 

For each of the following polymers, indicate whether they are addition or condensation polymers LLDPE, nylon 6,6, PVC, PC, PAN, PP, HDPE, PET, LDPE, and PVDC. Write their chemical structures. 

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