Ring caprolactam

This group of polyesters is made by the opening of the caprolactam ring. Caprolactam is also used in the production of nylon. Their structure appears to provide a degree of protection from hydrolytic attack. They are formed by the reaction shown in Figure 2.13 (Barbier-Baudry and Braachais, 2003). Their hydrolytic properties fall between those of PTMEG and other polyesters. 

Nylon-6 is the polyamide formed by the ring-opening polymerization of S-caprolactam. The polymerization of S-caprolactam can be initiated by acids, bases, or water. Hydrolytic polymerization initiated by water is often used in industry. The polymerization is carried out commercially in both batch and continuous processes by heating the monomer in the presence of 5—10% water to temperatures of 250—280°C for periods of 12 to more than 24 h. The chemistry of the polymerization is shown by the following reaction sequence. 

HO—R—COOH, or an amino acid, H2N—R—COOH. In some cases, such monomers self-condense to a cycHc stmcture, which is what actually polymerizes. For example, S-caprolactam (1) can be thought of as the self-condensation product of an amino acid. Caprolactam undergoes a ring-opening polymerization to form another... 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Caprolactam was first successfully polymerized to Pedon in 1938 by I. G. Farben and the associated technology was acquired as a part of postwar reparations by the Western AUies and the former USSR (1). By 1965 other countries, eg, Italy and Japan, had developed their own caprolactam processes, each involving nitrosation of an aUphatic ring. 

Reaction-Injection Molding and Reactive Casting. Reaction-iajection molding (RIM) (22) and reactive casting (23) have been demonstrated on nylon-6, which is polymerized by catalytic ring opening and linear recondensation of S-caprolactam (qv) (24). 

The preparation of nylon resins from lactam precursors involves ring opening, which is facihtated by a controlled amount of water in the reaction mixture. The salt complex condenses internally to produce the polyamide (57). The synthesis of nylon-6 [25038-54-4] from S-caprolactam is as follows ... 

Action of catalytic amounts of vanadium compounds on oxaziridine (52) yields caprolactam almost quantitatively. Reductive opening of the oxaziridine ring and /3-scission yield radical (118), which recyclizes with elimination of the metal ion to form the lactam (63) (77JPR274). 

One variation of rearrangement polymerisation is ring-opening polymerisation. Important examples include the polymerisation of trioxane, ethylene oxide and e-caprolactam Figure 2.8 (a) to (c) respectively). It is to be noted that... 

The opening of the caprolactam ring for nylon 6 involves an equilibrium reaction which is easily catalysed by water. In the case of nylon 12 from dodecanelactam, higher temperatures, i.e. above 260°C, are necessary for opening the ring structures but since in this case the condensation is not an equilibrium reaction the process will yield almost 100% of high polymer. ... 

The major aromatics (organics having at least one ring structure with six carbon atoms) manufactured include benzene, toluene, xylene, and naphthalene. Other aromatics manufactured include phenol, chlorobenzene, styrene, phthalic and maleic anhydride, nitrobenzene, and aniline. Benzene is generally recovered from cracker streams at petrochemical plants and is used for the manufacture of phenol, styrene, aniline, nitrobenzene, sulfonated detergents, pesticides such as hexachlorobenzene, cyclohexane (an important intermediate in synthetic fiber manufacture), and caprolactam, used in the manufacture of nylon. Benzene is also used as a general purpose solvent. 

Ring opening polymerization produces a small number of synthetic commercial polymers. Probably the most important ring opening reaction is that of caprolactam for the production of nylon 6 ... 

Although no small molecule gets eliminated, the reaction can be considered a condensation polymerization. Monomers suitable for polymerization by ring opening condensation normally possess two different functional groups within the ring. Examples of suitable monomers are lactams (such as caprolactam), which produce polyamides, and lactons, which produce polyesters. 

Nylon resins are important engineering thermoplastics. Nylons are produced by a condensation reaction of amino acids, a diacid and a diammine, or by ring opening lactams such as caprolactam. The polymers, however, are more important for producing synthetic fibers (discussed later in this chapter). 

Nylon 6 is produced by the polymerization of caprolactam. The monomer is first mixed with water, which opens the lactam ring and gives w-amino acid ... 

Ring-opening reactions may also be used in order to make polymers by the step polymerisation mechanism. One commercially important example of this is the manufacture of nylon 6, which uses caprolactam as the starting material and proceeds via the ring-opening reaction shown in Reaction 2.15. 

Step growth polymerization can also take place without splitting out a small molecule. Ring-opening polymerization, such as caprolactam polymerization to nylon 6, is an example. Polyurethane formation from a diol and a diisocyanate is another step growth polymerization in which no small molecule is eliminated. 

Nylon 66 is a condensation polymer made from adipic acid and iiexamethylenediamine. Nylon 6 is made by ring-opening polymerization of caprolactam. 

Activated carboxylic acids served as versatile precursors in lactam synthesis. Robl described some a-amino-c-alkyl-c-caprolactam syntheses, Eqs. (4-7)] [12]. Ring closure was induced after an EDC/HOBt activation of the acid function of 31 to form the 6-propyllactam 32 in 51 % yield, Eq. (4). The cyclization of... 

Dutton reported on the synthesis of an e-caprolactam analog of an anthelmintic cyclic peptide. The a-hydroxy-e-caprolactam 44 was generated in an ex chiral pool synthesis staring from malic acid. The a-hydroxy carboxylic acid unit was protected as a dioxolanone in 43. The protective group served simultaneously as the reactive function during cyclization lactam 44 formation succeeded by ring opening of the dioxolanone 43 by the nucleophilic attack of the amino function, Eq. (8) [14]. 

Rhodium carboxylates have been found to be effective catalysts for intramolecular C—H insertion reactions of a-diazo ketones and esters.215 In flexible systems, five-membered rings are formed in preference to six-membered ones. Insertion into methine hydrogen is preferred to a methylene hydrogen. Intramolecular insertion can be competitive with intramolecular addition. Product ratios can to some extent be controlled by the specific rhodium catalyst that is used.216 In the example shown, insertion is the exclusive reaction with Rh2(02CC4F9)4, whereas only addition occurs with Rh2(caprolactamate)4, which indicates that the more electrophilic carbenoids favor insertion. 

The polymerization process for nylon 6 consists primarily of the three types of reaction illustrated in Fig. 23.6. Each of the reactions is reversible, tvith the equilibrium of the products being controlled primarily by the concentration of water in the reaction vessel. The reaction is initiated by the hydrolytic ring opening of caprolactam to form 6-aminohexanoic acid, as shown in Fig. 23.6 a). Chain extension of the type shotvn in Fig. 23.6 b) dominates when water is abundant (10 to 20%) in the reaction mixture. At lower water levels (2 to 5%) chains grow primarily by the mechanism shown in Fig. 23.6 c). In order to limit the average molecular... 

Why does water content affect the chain extension step of the hydrolytic ring opening of caprolactam ... 

Polyamide 6 is produced by ring opening polycondensation of e- caprolactame. If no other reactants are used, the polymer chains contain one carboxylic acid and one amine end group. 

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