Polyamide synthesis from nylon salts

Polyamide Synthesis from Nylon Salts. The polycondensation of nylon salts was also accelerated by the microwave irradiation (Eq 2). 

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 ... 

Acid anhydride-diol reaction, 65 Acid anhydride-epoxy reaction, 85 Acid binders, 155, 157 Acid catalysis, of PET, 548-549 Acid-catalyzed hydrolysis of nylon-6, 567-568 of nylon-6,6, 568 Acid chloride, poly(p-benzamide) synthesis from, 188-189 Acid chloride-alcohol reaction, 75-77 Acid chloride-alkali metal diphenol salt interfacial reactions, 77 Acid chloride polymerization, of polyamides, 155-157 Acid chloride-terminated polyesters, reaction with hydroxy-terminated polyethers, 89 Acid-etch tests, 245 Acid number, 94 Acidolysis, 74 of nylon-6,6, 568... 

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... 

In the synthesis of nylon 66, hexanedioic acid and 1,6-hexanediamine are dissolved in aqueous ethanol, in which they react to form a one-to-one salt called nylon salt. This salt is then heated in an autoclave to 250 °C and an internal pressure of 15 atm. Under these extreme conditions, —COO groups from the diamine and —NHs" groups from diamine react by the loss of HgO to form a polyamide. Nylon 66 formed under these conditions melts at 250 to 260 °C and has a molecular weight ranging from 10,000 to 20,000 g/mol ... 

In the series of papers, synthesis of aliphatic polyamides and polyimides under microwave irradiation was described by Imai et al. [67-71]. The reactions were carried out in a modified domestic microwave oven with a small hole on the top of the oven so that nitrogen was introduced to a 30 ml wide-mouth vial adapted as a reaction vessel. In the case of polyamides synthesis, they were prepared of both CO-amino acids and nylon salt type monomers while polyimides were obtained from the salt form of monomers composed of aliphatic diamines and pyromellitic acid or its diethyl ester in the presence of a small amount of a polar organic medium (Fig. 11). 

Fig. 11. Microwave-assisted synthesis of various polyamides from co-amino acids and nylon salts. Reprinted from (1996) React Funct Polym 30 3 [70] with permission...

The synthesis of aliphatic polyamides under microwave irradiation has already been reported in a number of papers. " Polyamides were prepared from both co-amino acids and diamines together with dicarboxylic acids (i.e., the nylon salt-type monomers) in the presence of a small amount of a polar organic medium (Figure 32). 

Table 2. Microwave-Assisted Synthesis of Various Polyamides from Both (o-Amino Acids and Nylon Salts ...

Imai (1996a) developed a new facile method for the rapid synthesis of aliphatic polyamides and polyimides from polycondensation of ra-antino acids and nylon salts. The polymerization reactions were carried out in domestic nticrowave oven in the presence of a small amount of a polar organic medium. Suitable organic media for the polyamide synthesis are tetramethylenesulfone (TMS) amide-type solvents such as N-cyclohexyl-2-pyrrolidone (CHP), 1, 3-dimethyl-2-imidazoUdone (DMI), phenolic solvents like m-cresol and o-chlorophenol, etc. and for the polyimide synthesis amide-type solvents such as N-methyl-2-pyrrolidone (NMP), CHP and DMI. In polyamide synthesis, the polycondensation was almost complete within 5 min, producing a series of polyamides with inherent viscosities aroimd 0.5 dL/g, and the polyimides having the viscosity values above 0.5 dL/g were obtained within 2 min. 

Another example of bulk (or melt) polymerization is the synthesis of polyamides through the direct interaction between a dicarboxylic acid and a diamine. Nylon 66, for example, can be produced from the reaction between hexamethylenediamine and adipic acid. In practice, it is preferable to ensure the existence of a 1 1 ratio of the two reactants by prior isolation of a 1 1 salt of the two. The overall procedure is summarized by the reaction scheme ... 

---