Ring opening polymerization of lactams

K. Hashimoto, Ring-Opening Polymerization of Lactams. Living Anionic Polymerization and Its Applications , Prog. Polym. Sci. 2000, 25, 1411-1462. 

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... 

Hydrolytic polymerization of e-caprolactam to form nylon 6 (Sec. 2-8f) is carried out commercially in both batch and continuous processes by heating the monomer in the presence of 5-10% water to temperatures of 250-270°C for periods of 12 h to more than 24 h [Anton and Baird, 2002 Zimmerman, 1988]. Several equilibria are involved in the polymerization [Bertalan et al., 1984 Sekiguchi, 1984]. These are hydrolysis of the lactam to e-amino-caproic acid (Eq. 7-56), step polymerization of the amino acid with itself (Eq. 7-57), and initiation of ring-opening polymerization of lactam by the amino acid. The amino acid is... 

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. 

Chemistry of Anionic Ring Opening Polymerization of Lactams. 8... 

Anionic ring opening polymerization of lactams to generate polyamides has been studied quite extensively by Sebenda [8-10], Sekiguchi [11], and Wichterle [12-13], among others, in academia, and by Gabbert and Hedrick [14] and by us [23-25] in industry. By far, caprolactam is the most studied lactam and the nylon 6 prepared by this route compares favorably in properties with that prepared by conventional hydrolytic polymerization. 

Polymerization of oxirane (and of its derivatives) by the mechanism of activated monomer is so far exclusively cationic and can be represented by schemes (27) and (28) of Chap. 4. In contrast to the ring-opening polymerization of lactams, both the classical and the activated monomer mechanisms are operating in this case. Conditions can be found where one or the other mechanism predominates [339]. 

The formation of polyamides by ring-opening polymerization of lactams can proceed through several types of reversible transacylation reactions in which the lactam amide bond is cleaved while a polymer amide bond is formed, viz. 

Synthetic PAs are produced by polycondensation of bifunctional monomers or by cationic and anionic ring-opening polymerization of lactams. Polymers obtained with the first technique are linear, whereas chain branching may occur with anionic polymerization. Based on their chemical structure, synthetic polyamides may be classified into two categories [1] ... 

Cationic ring-opening polymerization of lactams 85MI16. 

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. 

Lactams are cyclic amides formed by the intramolecular amidation of amino acids. The ring-opening polymerization of lactams [Eq. (10.34)], especially caprolactam (m = 5), provides a valuable noncondensation route to the synthesis of nylons q... 

Memeger, W., Jr, Campbell, G.C. and Davidson, F. (1996) Poly(aminophosphazene)s and protophosphatranes mimic classical strong anionic base catalysts in the anionic ring-opening polymerization of lactams. Macromolecules, 29, 6475-6480. 

Equation 2.2 and Equation 2.3 pertain to the polycondensation of amino acids and to the ring-opening polymerization of lactams for the synthesis of AB-type nylons, respectively ... 

J. Sebenda, Chapt. 8 in Polymerization ofHeterocyclics (O. Vogl and J Furukawa, eds.), Dekker, New York, 1973 J. Sebenda, Anionic Ring-Opening Polymerizations of Lactams, Chapt. 35 in Comprehensive Polymer Science, Vol. 3 (G.C. Eastmond, A. Ledwith, S. Russo, and P. Sigwaldt, eds.), Peigamon Press, London, 1989. M. Rothe, H. Boenisch, and D. Essig, Makromol. Chem., 91,24 (1966). 

In this case, the monomeric unit is not structurally identical with the initial monomer consequently, there are no monomer-polymer equilibria, and so it differs from the normal ring-opening polymerization of lactams. 

Several reaction mechanisms were offered to explain the mechanism of anionic ring-opening polymerizations of lactams. One mechanism is based on nucleophilic attacks by the lactam anions at the cyclic carbonyl groups of N-acylated lactams. This leads to formations of intermediate symmetrical mesomeric anions that rearrange with openings of the rings [133, 134] ... 

The nylons are named by the number of carbon atoms in the repeat units. The materials formed by ring opening polymerizations of lactams, therefore, carry only one number in their names, Uke, for instance, nylon 6 that is formed from caprolactam. By the same method of nomenclature, a nylon prepared by condensing a diamine with a dicarboxylic acid, like, for example, hexamethylene diamine with adipic acid, is called nylon 6,6. It is customary for the first number to represent the number of carbons in the diamine and the second number to represent the number of carbons in the diacid. A discussion of various individual nylons follows. Not all of them are industrially important. 

Hashimoto, K. 2000. Ring-opening polymerization of lactams. Living anionic polymerization and its applications. Progress in Polymer Science 25(10) 1411-1462. 

Scheme 7.7. Activated anionic mechanism for ring-opening polymerization of lactams.

Luisier A, Bourban P E and Manson J A E (2002) Initiation mechanisms of anionic ring-opening polymerization of lactam-12, J Polym Sci Polym Chem Ed 40 3406-3415. Yamashita Y, Matsui H and Ito K (1972) Block copolymerization V. Block anionic polymerization of lactams, J Polym Sci Polym Chem Ed 10 3577-3587. 

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