Acyl lactam

Anionic polymerization of lactams was shown to proceed according to what is called the activated monomer mechanism. With bischloroformates of hydroxy-terminated poly(tetramethyleneglycol) and poly(styrene glycol) as precursors for a polymeric initiator containing N-acyl lactam ends, block copolymers with n-pyrrol-idone and e-caprolactam were obtained by bulk polymerizations in vacuum at 30 and 80 °C, respectively361. ... 

F. P. Bonina, L. Montenegro, G. Trapani, M. Franco, G. Liso, In vitro Evaluation of N-Acyl Lactam Esters of Indomethacin as Dermal Prodrugs , Int. J. Pharm. 1995, 124, 45-51. 

Lactam polymerizations (nonassisted as well as assisted) are usually complicated by heterogeneity, usually when polymerization is carried out below the melting point of the polymer [Fries et al., 1987 Karger-Kocsis and Kiss, 1979 Malkin et al., 1982 Roda et al., 1979]. (This is probably the main reason why there are so few reliable kinetic studies of lactam polymerizations.) An initially homogeneous reaction system quickly becomes heterogeneous at low conversion, for example, 10-20% conversion (attained at a reaction time of no more than 1 min) for 2-pyrrolidinone polymerization initiated by potassium t-butoxide and A-benzoyl-2-pyrrolidinone. The (partially) crystalline polymer starts precipitating from solution (which may be molten monomer), and subsequent polymerization occurs at a lower rate as a result of decreased mobility of /V-acyl lactam propagating species. 

Successive addition of monomers to the end of macromolecular initiator is the usual technique for the synthesis of tailored blockcopolymers. Anionic polymerization of pivalolactone, a-pyrrolidone— and the NCA of T-methyl-D-glutamate -2 was started from the end group of a prepolymer consisting carboxylate group or acyl lactam group or amino group. Living polymer of C-capro-lactone was expected to be formed by the initiated polymerization from polymer carbanion under kinetic controlled condition. 

Sehring and Konz reported in 1956 that the reaction of lactim ethers with acid chlorides results in O-acyl lactims.105 In 1965, however, Stolle and Griehl108 stated that the earlier work was erroneous N-acyl lactams were formed (Scheme 17), and this certainly seems more likely. 

Polymerization of 2-pyrrolidone is also activated by various A-acyl lactams, especially by iV-acetyl-2-pyrrolidone, lower lactones, CO, and JV-benzoyllac-tams [211]. 

Cationic polymerization is the only route, however, for the polymerization of iV-substituted (N-alkyl and Af-acyl) lactams the resulting polyamides have much lower melting points than their unsubstituted analogs due to the absence of hydrogen bonding. 

This undesirable side reaction is avoided in the polymerization of N-substituted lactams i.e., N-alkyl, N-aryl, or N-acyl lactams. Polymerization of N-substituted lactams proceeds differently, thus in the presence of hydrogen chloride the following sequence of reactions takes place [217]. 

The acceleration at the start of the polymerization (Fig. 8, curve 1) represents an induction period in which certain active species are formed gradually. It has been established that the active chain growth centre is represented by an A/-acylated lactam [44, 83, 85—94] which is formed in the slow disproportionation reaction... 

The high speed of anionic polymerization is due to the fact that both reacting species are chemically activated and hence highly reactive the lactam anion represents an activated monomer with increased nucleo-philicity and the terminal N-acylated lactam unit represents an activated end group (growth centre) with increased acylating ability. 

A great variety of substances is capable of acting as activators. The first group comprises iV-substituted lactams with polar substituents at the nitrogen. These iV-substituted lactams must be able to acylate lactam anions with opening of the lactam ring of the activator at a rate comparable to the rate of polymerization. The main representatives of this group are acyllactams [84, 89, 107—110] (V), iV-substituted [111] (VI) or iV,Af-disubstituted [112] carbamoyllactams (VII), JV-carboxylic acid esters of lactams [112] (VIII) and salts of lactam-N-carboxylie acids [107] (IX), viz. 

However, it follows from the processes discussed so far that in some reactions growth centres are also regenerated. For example, decomposition of the anion of a substituted keto amide yields lactam anions as well as isocyanate which is an effective activator, reaction (35). Acyl-lactam growth centres are also generated from keto amide and isocyanate, scheme (45). At high temperatures, lactam anions are generated also from carbonate [130,145,146]... 

Substitution at the nitrogen atom decreases the polymerizability of small and medium lactams much more than substitution at any other ring atom (see Section 3) and, therefore, only the highly strained four-, eight-and nine-membered N-substituted lactams have been polymerized so far [53,241—243] (Table 11). Because of the lack of a dissociatable hydrogen at the amide group, A/ -substituted lactams cannot form the chemically activated species required for the anionic polymerization, i.e. lactam anions and AT-acylated lactam an anionic propagation could proceed only... 

Number of polymer molecules formed per acyl lactam as a function of initiator concentration in the case... 

Recently, however, Sebenda3) has proposed that in polymerization of the highly reactive N-acyl lactams initiated with salts bearing stable complex anions like AsF chain growth proceeds with polymeric acylium cations by attack at the N-atom and not at the O-atom as usually proposed ... 

Spectroscopic (NMR, IR) studies show, that protonation (or coordination with Lewis acids) occurs predominantly at the oxygen atom as depicted in Eq. (11-3)5,6). In the absence of other strong bases the positively charged C-atom in the protonated monomer is attacked by the N-atom of another lactam and primary amino- and N-acyl lactam end-groups are formed (11-3) ... 

Sodium or magnesium caprolactam salt is produced by reaction of sodium hydride or a Grignard reagent with caprolactam. A rapid polymerization occurs when the acylated lactam, the catalyst, and monomer are mixed at temperature at or greater than 140°C. This polymerization is usually carried out in a two-stream reactor in which one stream contains the catalyst dissolved in the monomer and the second stream contains the initiator dissolved separately in the monomer ... 

Coupling of iV-Acyl Lactams with Aldehydes or Ketones. 

Treatment of IV-acyl lactams with samarium iodide leads to an acylsamarium species that is trapped by ketones or aldehydes (eq 56). ... 

Care must be taken with this reaction, and an alternative procedure is to use a two-component catalyst system by reacting the lactam with a base to produce an activated monomer. This then reacts with a promoter such as the acyl lactam, which initiates the ring-opening growth of the linear polymCT. For a series of cychc lactams, the reaction rates are a function of ring size and are in the order of 8- > 7- > 11- 5- or 6-membered rings. These are important commercial processes, and nylon-4 is also prepared vising this type of reactioiL... 

The initiation reaction yields an imide moiety, which constitutes a growth center for propagation reaction. Addition of certain imides such as acyl lactams as coinitiators essentially eliminates the initiation reaction and makes possible the polymerization at relatively low reaction temperatures. Mechanistic and kinetic aspects of the anionic polymerization of lactams have been treated quite extensively [16b]. The discussed subjects relate to the various equilibria governing the polymerization process. They comprise equilibria allied to monomer conversion, to the formation of cyclic oligomers, and to the effect of initiator concentrations. 

Generally, the initiators activate the inactive amide groups, causing them to react with other lactams through successive transamidations that result in formations of polyamides. Both acids and bases catalyze the transamidation reactions. The additions of electrophiles affect increases in the electrophilicity of the carbonyl caibon of the acylating lactam. The nucleophiles, on the other hand, increase the nucleophilic character of the lactam substrate (if they are bases). 

The third step is propagation. It consists of addition of a unit to the chain end and takes place upon reaction of the terminal acyl lactam with a sodium salt of 2(dialkoxyaluminoxy)-l-azacycloheptane shown above... 

Thus the lactam polymerization with strong bases can be strongly accelerated by addition of activators such as, for example, acyl lactams. Additionally, the acyl lactam may be formed in situ by adding acetic anhydride or ketenes to the polymerization mixture. 

Polymerization via monomer anions without added activator behaves quite differently. In this case, theo>-amino acyl lactam activator is first formed in a slow reaction, and then, the polymer chain is started in a fast subsequent reaction. Further a>-amino acyl lactam molecules are formed continuously during the polymerization. Only when all base molecules react with monomer molecules before the other monomer molecules are consumed by formation of polymer chains is the degree of polymerization given by the ratio of monomer to base concentration. Since this is mostly not the case, there is no relationship between the ratio [monomer]/[base] and the degree of polymerization. Similar relationships occur for the polymerization of iV-carboxy anhydrides of a-amino acids with strong bases. 

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] ... 

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