Polyamides from lactams

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 ... 

Lactams -from bromine [BROMINE] (Vol 4) -polyamides from [POLYAMIDES - GENERAL] (Vol 19)... 

The third major method for achieving difunctionality involves the ring-opening polymerization of a cyclic monomer, typified for example by the synthesis of polyamides from cyclic lactams. Reactions of this type proceed by chain-reaction mechanisms but yield polymers more typical of step-reactions, in that they contain functional groups within the chain. 

There is an alternative naming system for synthetic polyamides from unsubstituted nonbranched aliphatic monomers. A polyamide made from either an amino acid or a lactam is called nylon x, where x is the number of carbon atoms in the repeating unit. A nylon made from a diamine and a dibasic acid is designated by two numbers, in which the first represents the number of carbons in the diamine chain and the second the number of carbons in the dibasic acid. 

In addition to step and chain polymerizations, another mode of polymerization is of importance. This is the ring-opening polymerization of cyclic monomers such as cyclic ethers, esters (lactones), amides (lactams), and siloxanes. Examples of commercially important types are given in Table 10.1. Of those listed, only the polyalkenes are composed solely of carbon chains. Those that have enjoyed the longest history of commercial exploitation are polyethers prepared from three-membered ring cyclic ethers (epoxides), polyamides from cyclic amides (lactams), and polysiloxanes from cyclic siloxanes. 

In addition to the polymerisation of pure lactones, these cyclic [di] esters have already been included as co-monomer to improve the properties of closely related polymers like polyamide obtained starting from lactams [86]. 

In the early days of macromolecular chemistry, synthetic polymers were simply labeled according to the monomer from which they were prepared. Thus, ethylene polymers became poly(ethylenes), styrene polymers became poly(styrenes), and those from lactams became poly (lactams). In other cases, the choice of name was provided by a characteristic group occurring in the final polymer. Thus, polymers from diamines and dicarboxylic acids were called polyamides, and those from diols and dicarboxylic acids were called polyesters. This phenomenological nomenclature fails, of necessity, when more than one kind of monomeric unit can be formed from a given monomer. 

Polyamide the abbreviation PA is normally followed by a number, a combination of numbers, a letter, or a combination of letters and numbers. A single number refers to the polyamide from an a,co-amino acid or its lactam. A combination of two numbers is often separated by a comma. The first number following the symbol PA indicates the number of methylene groups of aliphatic diamines and the second number the number of carbon atoms of aliphatic dicarboxylic acids. An I stands for isophthalic acid and a T for terephthalic acid. For example, co-polyamide from caprolactam, hexamethyle-nediamine condensed with isophthalic and terephthalic acids... 

During the course of these studies, W.H. Carothers and G.J. Berchet in 1930, extending the early work of von Braun, investigated the self-condensation of e-aminocaproic acid [ ]. They obtained a low-molecular polyamide. From cryoscopic measurements in phenol they inferred a degree of polymerization of at least 10. In the same paper they stated that caprolactam "does not polymerize under the conditions of formation of the polyamide either in the presence or absence of catalysts". As practically no experimental details were given, one can only speculate about the reason of this failure. Perhaps they were influenced by the fact that the corresponding 5- and 6-membered lactams did not polymerize either - an explanation offered later by P. Schlack [s]. 

Polyamides made from lactams and amino acids. 

When lactams are homopolymerized or short chain dibasic acids are reacted with diamines, high melt point polyamides suitable for fibers or engineering plastics are obtained. Nylons derived from lactam or amino acids are designated by the number of caibon atoms in the amino acids, while the nylons derived from the reaction of dibasic acids and diamines are given two numbers, the number of carbon atoms in the diamine and dibasic acid respectively ... 

P-lactams. Monomers having a low rate constant of propagation are preferable for the synthesis of uniform polyamides. Drawbacks in the preparation of uniform polyamides from P-lactams are the very frequent occurrence of depolymerization and transamidation (at the acyl lactam chain end and on the polyamide chain), both causing broadening of molar mass distribution of the resultant polyamide. The latter reaction occurs more frequentiy at high conversion. Therefore, it is advisable to stop the polymerization at low to intermediate... 

On the basis of the results obtained so far using the three methods mentioned above, a relevant conclusion can be drawn the accurate temperature control (S 170 ° C) permits to mn polymerizations of CL in quasi-isothermal conditions and very efficiently contribute to the minimization of side reactions, the other relevant factor in this respect being the use of very fast activator/initiator pairs. Only the simultaneous effect of both factors, that is, temperature control and very fast catalytic systems, allows to reach both optimum process conditions and excellent polymer properties. The use of slow activators, such as N-acetyl-CL, on the contrary, strongly limits possible advantages of the method. Moreover, it should be taken into account that in general, solution polymerizations (methods 1 and 3) ate characterized by lower reaction rates as compared to suspension processes (method 2). On the other hand, these latter methods have to face more difficult and expensive purification procedures of the polyamide from the reaction mixture. The only other lactam-based polyamide synthesized in powder form in laboratory by a suspension process is poly(2-pyrrolidone). A description of its synthesis is given in Section 4.14.11.1. 

The AB polyamides are made from either >-amino acids or cyclic lactams, derivatives of the oj-amino acids (Table 3.1). In these polymers, the amino and acid groups are inherently balanced and the polymer also contains one amino and one acid endgroup. There are a number of different routes available for polymerizing these AB-type polyamides ... 

In common with all the higher AB polyamides, PA-12 can be made from either die amino acid or the lactam.12 In practice, PA-12 is made from the cheaper 12-laurolactam (12-dodecane lactam or laboratory-scale synthesis it is advisable to start with the amino acid or a combination of amino acid and lactam. 

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... 

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. 

A chiral p-polyamide 83 of the Nylon 3 type was also synthesized [68, 69] by Galbis et al. by ring-opening polymerization of the p-lactam derived from 3-amino-3-deoxy-2,4,5,6-tetra-(9-methyl-D-altronic acid. 

Some other chiral Nylon 3 analogs have also been prepared by the same authors applying ring-opening polymerization of chiral p-lactams 84 derived from D-glyc-eraldehyde [70,71], The enantiomerically pure (2R,3R) and the racemic (2R,3R and 2S,3S) p-polyamides were obtained, and their properties compared. 

Nylon 6 is also a polyamide, but is made from the monomer e-caprolactam, which is a cyclic amide of e-aminocaproic acid. Heat opens the lactam ring to give the amino acid salt, which forms amide bonds with other molecules by eliminating water. 

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