Aliphatic polyamides caprolactam

The United States accounts for about a third of the world s consumption of cyclohexane, or 3.785 x 10 m /yr (about 1 biUion gallons per year). U.S. producers and their 1990 capacities are Hsted in Table 13. Texaco has aimounced that it is leaving the cyclohexane business, but the timing is not yet certain. Over 90% of all cyclohexane goes to the production of nylon through either adipic acid (qv) or caprolactam (qv). The balance is used to produce 1,6-hexamethylenediamine [124-09-4] (HMD A) and for various solvent uses (see Diamines and higher amines, aliphatic Polyamides). 

Aliphatic polyamides of e-caprolactam (Nylon-6) possess great importance as fibers and plastics. 

It has become the custom to name linear aliphatic polyamides according to the number of carbon atoms of the diamine component (first named) and of the dicarboxylic acid. Thus, the condensation polymer from hexamethylenedi-amine and adipic acid is called polyamide-6,6 (or Nylon-6,6), while the corresponding polymer from hexamethylenediamine and sebacoic acid is called polyamide-6,10 (Nylon-6,10). Polyamides resulting from the polycondensation of an aminocarboxylic acid or from ring-opening polymerization of lactams are indicated by a single number thus polyamide-6 (Nylon-6) is the polymer from c-aminocaproic acid or from e-caprolactam. 

Polyamides are obtained either by the condensation of a dicarboxylic acid and an alkylene diamine or by the head-to-tail condensation between an amino carboxylic acid or the corresponding lactam. Polyamides may have aliphatic or aromatic chain backbones. Aliphatic polyamides (nylon) have the most important commercial applications, mainly in the manufacture of fibres. Nylon-6 and nylon-6,6 account for around 85% of all nylon currently used. Nylon-6 is derived from the polymerization of e-caprolactam, whereas nylon-6,6 is obtained by the condensation of hexamethylene diamine and adipic acid. 

Cyclohexanone, a six-membered carbon ring with a ketone as functional group, is almost exclusively applied as a precursor for the production of aliphatic polyamides. Pure cyclohexanone is mainly converted, via cyclohexanone oxime and caprolactam, to nylon-6 (also called polycaprolactam) [1]. Mixtures of cyclohexanone and cyclohexanol, often called K4 oil, are converted via oxidation into adipic acid that reacts with hexamethylene diamine (HMDA) to nylon-6,6 (poly-hexamethylene adipamide). Other applications of these products can be found in the field of polyurethane and polyester production. 

The characteristics of the thermal degradation have been studied most fully for aliphatic polyamides [1-3], from which cyclic monomers are split rather readily. Thus, of the volatile products of the thermal degradation of polycaproamide at temperatures above 300 °C, mainly e-caprolactam is observed in a dry inert atmosphere. Simultaneously the molecular mass of the polycaproamide decreases. The monomer is supposed to be released via a depolymerisation reaction proceeding from terminal COOH groups ... 

In addition to caprolactam and water, considerable quantities of carbon dioxide, ammonia, carbon monoxide, methane, and so on, are released via secondary reactions during the thermal degradation of aliphatic polyamides. Thus decarboxylation of the terminal COOH groups of polyamides results in release of carbon dioxide. Ammonia forms because of the self-interaction of terminal amino groups [2, 6] ... 

Class 1 nylons are usually polymerized from a stoichiometrically balanced condensation reaction of a diacid with a diamine. Nylon 6,6 is the most common and is used in fiber, specialty plastic, and electrical applications. Class 2 nylons are usually synthesized from the ring-opening polymerization of cyclic amides or lactams. For instance, nylon 6 is polymerized from -caprolactam. Cyclic aliphatic polyamides normally have better thermal stability than their linear counterparts. 

Dynamic-mechanical and dielectric data have been widely reported for most aliphatic polyamides, especially poly(g-caprolactam) (nylon-6 or PA-6 rg 313K) and poly(hexamethylene adipamide) (nylon-6,6 or PA-6,6 Tg 323 K). Results of dynamic-mechanical and dielectric measurements of PA-6 and PA-6,6 (Table 13.8) provide evidence for three relaxations (/3, y, and 8) in these polymers at temperatures below their crystalline-melting temperature Tni (487-506 K for PA-6 and 523-545 K for PA-6,6) [8]. The /3 relaxation (located at above 310-347 K for PA-6,6 and 357-370 K for PA-6,6) is associated with high... 

Nylon A class of synthetic fibres and plastics, polyamides. Manufactured by condensation polymerization of ct, oj-aminomonocarboxylic acids or of aliphatic diamines with aliphatic dicarboxylic acids. Also rormed specifically, e.g. from caprolactam. The different Nylons are identified by reference to the carbon numbers of the diacid and diamine (e.g. Nylon 66 is from hexamethylene diamine and adipic acid). Thermoplastic materials with high m.p., insolubility, toughness, impact resistance, low friction. Used in monofilaments, textiles, cables, insulation and in packing materials. U.S. production 1983 11 megatonnes. 

Special terminology based on trade names has been employed for some polymers. Although trade names should be avoided, one must be familiar with those that are firmly established and commonly used. An example of trade-name nomenclature is the use of the name nylon for the polyamides from unsubstituted, nonbranched aliphatic monomers. Two numbers are added onto the word nylon with the first number indicating the number of methylene groups in the diamine portion of the polyamide and the second number the number of carbon atoms in the diacyl portion. Thus poly(hexamethylene adipamide) and polyfhexamethylene sebacamide) are nylon 6,6 and nylon 6,10, respectively. Variants of these names are frequently employed. The literature contains such variations of nylon 6,6 as nylon 66, 66 nylon, nylon 6/6, 6,6 nylon, and 6-6 nylon. Polyamides from single monomers are denoted by a single number to denote the number of carbon atoms in the repeating unit. Poly(e-caprolactam) or poly(6-aminocaproic acid) is nylon 6. 

Aliphatic and alicyclic molecules such as cyclohexane undergo photosubstitution with nitrosyl chloride (Pape, l%7). The reaction is of considerable industrial importance in the synthesis of 6-caprolactam, an intermediate in the manufacture of polyamides (nylon 6). (Cf. Fischer, 1978.) At long wavelengths a cage four-center transition state between alkane and an excited nitrosyl chloride molecule is involved, as indicated in Scheme 63. In contrast to light-induced halogenation, photonitrosation has a quantum yield smaller than unity, and is not a chain reaction. 

Since 1935, when Carothers discovered the fiber-forming properties of polyamides, many chemists in the world have studied the synthesis of the raw materials for various polyamides, aliphatic diamines, aliphatic dibasic acids, caprolactam, and the w-amino fatty acids. The known synthetic routes to polyamides from w-amino fatty acids are as follows ... 

Commercial products are frequently referred to as nylons without further differentiation, and are distinguished from each other by numbers or letters. The numbers indicate the number of carbon atoms per aliphatic monomeric unit. Thus, nylon 6 or polyamide 6 is poly( -caprolactam). In the authentic nylon series, there are two numbers the first number refers to the number of carbon atoms in the diamine component and the second number to the number of carbon atoms in the dicarboxylic acid component. Consequently, nylon 6,6 or nylon 66 is poly(hexamethylene adipamide). Letters are often used to designate cyclic units, i.e., T for the terephthalic acid residue. 

The two main commercial polyamides are nylon 6,6, produced by condensation polymerization of HMD and adipic acid (see Table 7.1), and nylon 6, an AB-type polymer, which is produced from caprolactam. Other commercial polyamides include nylons 4,6, nylon 6,12 (which are AA- and BB-type polymers) and nylon 11 and nylon 12 (which are AB polymers made from linear aliphatic amino acids containing 11 and 12 carbons, respectively) [1]. Polyamides are also produced using monomers with aromatic, rather than aliphatic segments. Polyamides that contain 85% or more of the amide bonds attached to aromatic rings are called aramids. Commercial examples include poly(p-phenyleneterephthalamide) or Kevlar and poly(m-phenyleneisoterephthalamide) or Nomex [23]. 

Polyamides are abbreviated as PA, followed by the number of carbons in a diamine and dicarboxylic acid, viz., PA-66 has six carbons in each component, etc. Poly-E-caprolactam or polyamide-6 (PA-6) was first studied by Von Brown in 1905-1910, and 30 years later commercialized as PerloriP. In the year 1936, PA-66 and several other aliphatic and semi-aromatic polyamides were disclosed (Carothers 1937). Two years later, du Pont introduced Nylon . PA-11 was commercialized in 1955, PA-12 in 1966, PA-612 in 1970, and PA-46 in 1987. In 1976 du Pont started production of the super tough PA blends (Damm and Matthies 1990). In 1991 consumption of the thermoplastic PAs was estimated at 1.2 Mt. Comparative properties of the better-known PAs are listed in Table 1.54. 

Polyamide the abbreviation PA is normally followed by a number, a combination of numbers, a letter, or a combination of letters and numbers. A single number refers to the polyamide from an a,co-amino acid or its lactam. A combination of two numbers is often separated by a comma. The first number following the symbol PA indicates the number of methylene groups of aliphatic diamines and the second number the number of carbon atoms of aliphatic dicarboxylic acids. An I stands for isophthalic acid and a T for terephthalic acid. For example, co-polyamide from caprolactam, hexamethyle-nediamine condensed with isophthalic and terephthalic acids... 

In the rich assortment of polyamides an important position is held by aliphatic unsubstituted linear pdyamides, known under the current name of nylons. They are prepared either by polycondensation of aliphatic diadds and diamines or of aliphatic co-amino adds, or by pofyaddition of their lactams. The numera](s) following the term nylon indkate(s) the number of carbon atoms in the monoiiKric unit thus, e the pdymer of pytrolidone is called nylon 4, that of caprolactam is nylon 6, the copolycondensate of hexamethyienedhimine and adipic add is nylon 6,6 and the copolycondensate of hexamethylenediamine and sebadc add is nylon 6,10. 

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