Ring-opening polymerization nylon production

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 ... 

Among the more common thermoplastics from ring opening polymerization of interest in composite processing are polylactams, polyethers, polyacetals, and polycycloolefins. It has also been shown that polycarbonates can be produced from cyclic carbonates [22], Anionic ring opening polymerization of caprolactam to nylon 6 is uniquely suited to form a thermoplastic matrix for fiber-reinforced composites, specifically by the reaction injection pultrusion process [23-25]. The fast reaction kinetics with no by-products and the crystalline... 

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. 

Nylon 6,6 and nylon 6 are polyamides. These polymers are used in carpets, in hosiery, and in certain cases as engineering plastics. Nylon 6,6 8.19, is the condensation product between adipic acid and 1,6-diamino hexane. Nylon 6 8.20 is made from caprolactam by ring-opening polymerization. 

Polyamides are produced commercially by two routes. First is the polycondensation of aminoacids or diamines with diacids, and the second route is the ring-opening polymerization of lactams l. The ring-opening process can be accomplished with anionic or cationic initiators and also in the presence of water by a hydrolytic process. Nylon-6 (poly-e-caprolactam) and Nylon-12 (poly-co-dodecanelactam) are commercially produced mostly by the hydrolytic process, in which the reaction control is easier and the properties of the product better than in polycondensation. 

Commercial production of nylon-6,6 and its conversion into fibers was started by the Du Pont Company in 1939. In a parallel development in Germany, Schlack developed polyamides by ring-opening polymerization of cyclic lactams, and nylon-6 derived from caprolactam was introduced in 1939. Today nylon-6,6 and nylon-6 account for nearly all of the polyamides produced for fiber applications. 

The primary commercial route for nylon 6 production involves the ring-opening polymerization of caprolactam. The first stage of this process involves hydrolysis of the caprolactam monomer ... 

Nylon 4 or polypyrrolidone is an attractive polymer for use in fibers. The original syntheses of nylon 4 from 2-pyrroUdone were carried out by alkaline catalyzed ring opening polymerizations promoted by N-acylpyrrolidone [49]. The products from these reactions melt between 260 and 265°C. 

They are unstable at these temperatures and cannot be melt spun. Fibers, however, were prepared by dry spinning from hydrocarbon suspensions [49]. Later, it was found that when the anionic ring opening polymerizations of 2-pyrrolidone are activated by CO2 in place of the iV-acyl derivative, the resultant higher molecular weight product has much better heat resistance [54]. This new nylon 4, reportedly, can be melt spun. 

They include natural polymers such as silk and synthetics such as nylons. Nylon polymers first were synthesized by Wallace Carothers and CO workers at Du Point in the late 1920s and 1930s. They are derived from carboxylic acid and amine precursors by both condensation and ring opening polymerization. They are commonly named by adding to the word nylon, a number equal to the number of carbons in the parent compounds. Thus, nylon 6.6 is the product of the condensation reaction between hexamethylenediamine, NH2(CH2)eNH2, or HMD A, and adipic acid or its acid halide and methyl ester. 

The processing requirements for RIM are very stringent (a) the reactive streams must be effectively mixed by impingement (b) the system must not produce molding defects due to turbulence or advance polymerization (c) completion or near-completion of the polymerization must be achieved in an economically acceptable time and without excessive exotherms and (d) the reaction must be free of undesirable by-products. To date, very few polymerization systems have been used commercially with RIM. Polyurethanes account for over 90% of RIM materials produced. Other RIM systems include the anionic polymerization of caprolactam to produce nylon-6, and the ring opening polymerization of dicyclopen tadiene. Fillers are often incorporated into RIM formulations to lower raw material costs and to improve certain properties such as stiffness. 

Polyamides are produced by the reaction between a dicarboxylic acid and a diamine (e.g., nylon 66), ring openings of a lactam, (e.g., nylon 6) or by the polymerization of w-amino acids (e.g., nylon 11). The production of some important nylons is discussed in the following sections. 

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... 

Polymerization by a ring-opening reaction is confined to cyclic monomers which contain at least one heteroatom. The mechanism is very often a polyaddi-tion-type with a product which has a polycondensation-type character. For example, ethylene oxide and other cyclic esters can be polymerized into linear chains by this type of reaction. An even more complicated example of this type of polymerization reaction is the polymerization of e-caprolactam into Nylon 6 (PA 6). 

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