Lactam salts

Most of the work reported in the literature employs sodium lactamate salt as catalyst and isocyanate/lactam adducts as initiator. Gabbert and Hedrick [14] preferred to work with acyllactam as the initiator and Grignard salts of caprolactam as the catalyst in view of their ease of handling and fewer side reactions compared with the sodium lactamate and isocyanate system. 

A large number of compounds used as catalysts in acid-ion lactam polymerization are known. These include alkalis, alkali-earth metals, hydrates, Grignard reagents, lithium oxide, various hydroxides and carbonates, sulfates, halides, sodium zincate, alkaline salts of different acids, i.e., compounds that cause the formation of lactam acid ion in the reactive medium. The mechanism of polymerization in the presence of sodium-lactam- salt compounds is largely known. 

For the initiation of caprolactam polymerization, Grignard reagents [173] have been used as a source of lactamate salt. Tsuchiya and Tsuruta have described an interesting case of methyloxirane polymerization initiated with... 

At the beginning of polymerization, the concentration of lactam anions is determined by the dissociation of the lactam salt added as initiator, viz. 

Because of the lack of resonance stabilization, the amidium ion (XXIX) has an increased acylating ability and may acylate the nucleophiles present. At the beginning of the polymerization initiated with lactam salts of strong acids (e.g. lactam hydrochloride), the neutral lactam is a stronger nucleophile (pXb = 13.6) than the chloride anion (pXb = 21). Acylation of the lactam with the amidium cation (XXIX) results in the formation of an aminoacyllactam [178—181]... 

Kruissink [13, 220] demonstrated that the kinetics of the polyaddition is described satisfactorily by assuming two reactions, i.e. an uncatalysed addition of the lactam at the ammonium ion, reaction (118), and the carboxyl group catalysed addition of lactam at the neutral amine group. The catalysed reaction can be visualized as (92), in which the reactive species can be represented also by the undissociated lactam salt (or complex) [220] of increased acylating ability, viz. 

Ogata [244] found that the basicity of JV-substituted lactams is close to the basicity of the linear trans amide group. Therefore, it can be assumed that the basicity of the dialkylamide group and the ioni2ation constant of its salt is also the same for both the JV-alkyllactam and the corresponding open chain unit. The concentration of the lactam salt (XXX) or proto-nated lactam (XXXI) is then proportional to the lactam concentration, viz. 

Whereas the lactam salts reacted to form the target 2-mercapto-2H-l,4-benzoxazin-3 (4H)-onQ and 2-mercapto-2.W-1,4-benzothiazin-3 (4H)-om, respectively, their 4-hydroxy analogues underwent decomposition [126]. 

The above water-elimination reaction results in formations of amidines. Acylamidinium ions can also result from dehydration of the tetrahedral intermediates during the reactions of amino groups with acyllactams. Such groups could also be present within the polymer molecules. The water that is released in these reactions hydrolyzes the acyllactams, acylamidine salts, and lactam salts to yield carboxylic acids. ... 

The overall rates of polymerizations depend on the concentrations of acyllactams and diacy-lamine groups as well as on the lactam anions. The latter result form dissociations of the lactam salts, depending upon the nature of the metal ... 

Under conditions of complete dissociation, the concentration of the lactam anion, represented in the following discussions by -CO-N -, is equal to that of the lactam salt (II), denoted by LS. If LS is weakly dissociated, the concentration [-CO-N -J varies with [LS], since... 

The water released in these reactions subsequently hydrolyzes acyllactams, acylamidine salts and lactam salts to yield carboxylic groups. 

In the anionic polymerization, the monomer stmcture may have indirect efferts as well, influencing, for example, the dielectric properties of the reaaion medium and, thus, the course of the polymerization. Since lactam monomers and the resultant polyamides have polar amide bonds, their bulk polymerization rate is strongly affected by the changes in medium permittivity during polymerization. In anionic polymerization, high dielectric permittivities strongly favor the dissociation of the lactam salt (initiator) releasing the free lactam anion (Section 4.14.7.1). 

Fmnze et al proposed the participation of ion pairs of lactam salts in the propagation step and suggested an ion-coordination mechanism. According to this mechanism, a complex between the lactamate and the two carbonyl groups of the growing center is formed (Scheme 13). 

The lactam anion in the form of lactam salt (lactamate) can be obtained by in situ reaction with alkali metal compounds, or prepared ex situ and then introduced in the polymerization mixture. Some confusion may arise about the terms often used in the literature to identify the various compounds mentioned in previous sections (initiators, or catalysts, or precursors). In this chapter, we prefer to consider the lactamate as the tme initiator and the alkali metal compound as the precursor. A great niunber of precursors are able to generate... 

All of them have been studied in the anionic polymerization of CL, initiated with alkali metal lactam salts, and have found a more suitable application in the potymerization of 2-pyrrolidone at 30-50 °C, initiated by potassium 2-oxopyrro-lidin-l-ide. °... 

Thus, the initiation system of the activated polymerization has two components anionicaUy activated monomer (lactam salt) or its precursor are denoted nonuni-formly in the literature as, for example, the initiator, catalyst or activator similarly, the source of the nonionic growth center is called the promoter, catalyst, cocatalyst, chain initiator, initiator, coinitiator, activator, accelerator, and so on. In this chapter, the combined term initiator/activator wUl be used. 

An attempt to explain the mechanism of action of Synhydride has been made [34] wherein it was assumed that Synhydride first formed a classical lactam salt and A1H(0R)2 (Equation 7.13) ... 

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