Nylon salts

This compound is sometimes called a nylon salt. The salt polymer equilibrium is more favorable to the production of polymer than in the case of polyesters, so this reaction is often carried out in a sealed tube or autoclave at about 200°C until a fairly high extent of reaction is reached then the temperature is raised and the water driven off to attain the high molecular weight polymer. 

Reaction (5.N) describes the nylon salt nylon equilibrium. Reactions (5.0) and (5.P) show proton transfer with water between carboxyl and amine groups. Since proton transfer equilibria are involved, the self-ionization of water, reaction (5.Q), must also be included. Especially in the presence of acidic catalysts, reactions (5.R) and (5.S) are the equilibria of the acid-catalyzed intermediate described in general in reaction (5.G). The main point in including all of these equilibria is to indicate that the precise concentration of A and B... 

The reaction of diamines with dicarboxylic acids, via a nylon salt (Figure 18.1). 

Tankwater, Bright dip acid (phosphoric), Cyanide rinse hath, Pickle Liquor, Sodium AJuminate Liquor, N.S.S.C. Liquor, Kraft Liquor, Soda Liquor, Sulfite Liquor, Stillage, Corn Syrup, Gelatin, Salt, Soybean Oil, Steepwater, Sugar, Whey, Mercerizing Caustic, Nylon Salt, Rayon Spin Bath, and Sodium Sulfate. 

Processing and storage equipment for many chemicals, including acetaldehyde, formaldehyde, nylon salt, methyl methacrylate, carbon tetrachloride, glycerol, triacetin, proprionic acid, acetic acid and acetic anhydride, is manufactured from aluminium alloys, primarily because of their excellent corrosion resistance. 

PA-6,1 salt is made by adding 33.2 g of isophthalic acid to a reaction vessel with a reflux cooler filled with a 100-mL mixture of methanol and water (9 1). To this suspension, which is under nitrogen, 23.2 g of hexamethylene diamine in 20 mL of methanol is added slowly. The reaction mass is then allowed to cool whereby the nylon salt crystallizes. The precipitated salt is filtered, washed with methanol, and air dried. 

To a 50-mL straight-wall three-necked flask (Fig. 3.18b) equipped with a magnetic stirrer, nitrogen inlet/outlet, and condenser unit in a heating block are added 11.29 g of nylon salt and 0.093 g of hexamethylene diamine (2 mol % excess). This mixture is reacted for 2 h at 210° C and 3 h at 270°C. The resultant polymer is colorless and transparent and has a r/rei of 2.54 (1% solution in m-cresol, 25°C). 

In 1930, DuPont launched the synthetic fiber industry with the discovery of nylon-6,6.2 In 1938, a pilot plant for nylon-6,6 production was put into operation, and in 1939, production was commenced at a large-scale plant in Seaford, Delaware. The classical method for the synthesis of nylon-6,6 involves a two-step process. In the first step, hexamethylene diamine (HMDA) is reacted with adipic acid (AA) to form a nylon salt. Polymerization of the aqueous salt solution is carried out at temperatures in the range of about 210-275°C at a steam pressure of about 1.7 MPa. When 275°C is reached, the pressure is reduced to atmospheric pressure and heating is continued to drive the reaction to completion. 

For condensation polymerization, it is necessary to have two functional groups on each monomer and to mix stoichiometric amounts of the reactants. In polyamide production, the starting materials first form nylon salt by proton transfer ... 

At this point, the excess acid or amine can be removed. Then, when the nylon salt is heated, the condensation begins, just as in the preparation of simple amides. The first step is... 

Jmai", Y.i Rapid Synthesis of Polyimides from Nylon-Salt Monomers. Vol. 140, pp. 1-23. 

There are three methods by which we commercially manufacture nylons. We make nylons of the AB type by hydrolytic ring opening reactions of lactams and the self condensation of co-amino acids. Nylons of the AABB type are made from diamines and diacids via an intermediate know as a nylon salt. 

Manufacture of Type AABB Nylons via an Intermediate Nylon Salt... 

The diamine and diacid monomers used to make type AABB nylons are typically rather difficult to handle in their pure form. Diamines are liquids or semisolids at room temperature, while the diacids are crystalline solids. These monomers become much more manageable when they are combined to form nylon salts, as shown in Fig. 23.7 a). Nylon salts are solids that can be easily handled and ensure a stoichiometric balance between the diacid and diamine, which is necessary to produce high molecular weight polymers. In the case of nylon 66, the precursor salt is made by boiling adipic acid and hexamethylene diamine in methanol, from which the nylon salt precipitates. 

Figure 23,7 Reactions occurring during the polymerization of type MSB nylons via a nylon salt a) production of the nylon salt and b) condensation reaction...

What advantages are realized by the intermediate nylon salt method over direct polymerization of the diamines with the diacids ... 

EFFOL A process for making nylon salt (hexamethylenediamine di-adipate). Developed by Rhone-Poulenc in the 1980s and now used in its plant at Chalampe, France. It produces much less effluent than the earlier process. 

For the first method exact equivalence of reactants are used to obtain high Molecular weight polymer. In the first step an aqueous solution of adipic acid is neutralised with hexamethylene diamine to form nylon salt. 

Nylon salt can also be obtained by boiling methanol. 

The synthesis of polyamides follows a different route from that of polyesters. Although several different polymerization reactions are possible, polyamides are usually produced either by direct amidation of a diacid with a diamine or the self-amidation of an amino acid. The polymerization of amino acids is not as useful because of a greater tendency toward cycliza-tion (Sec. 2-5b). Ring-opening polymerization of lactams is also employed to synthesize polyamides (Chap. 7). Poly(hexamethylene adipamde) [IUPAC poly(iminohexanedioylimi-nohexane-l,6-diyl) or poly(iminoadipoyliminohexane-l,6-diyl)], also referred to as nylon 6/6, is synthesized from hexamethylene diamine and adipic acid [Zimmerman, 1988 Zimmerman and Kohan, 2001]. A stoichiometric balance of amine and carboxyl groups is readily obtained by the preliminary formation of a 1 1 ammonium salt (XU ) in aqueous solution at a concentration of 50%. The salt is often referred to as a nylon salt. Stoichiometric... 

A new commercial use for butadiene is its employment in the nylon synthesis joining furfural, benzene, and cyclohexane as raw materials for nylon salt components. Amother olefinic hydrocarbon, which has found large scale application in recent years, is propylene tetramer, widely employed in reaction with aromatic nuclei to yield an alkylated aromatic base used in synthetic detergent production. 

The mechanism for the production of nylon-12 from the lactam is similar to that for nylon. However, in the case of nylon-12, the ring opening is more difficult and the rate of polymerization is slower, at least in part owing to the lower solubility of the lactam in water. A catalyst such as an acid, amino acid, or nylon salt can serve as a ring-opening agent. Nylon-12 can also be produced via anionic polymerization, ie, polymerization using an anhydrous alkali catalyst. This process can be quite fast even at low temperatures, eg, a few minutes at 130°C. 

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