Acyllactam structure

In the copolymerization of lactams of different ring size, the relative rate of incorporation of the two lactams is not necessarily determined by the reaction in which the lactam ring is cleaved. Vofsi et al. [167] showed that in the anionic copolymerization of caprolactam and pyrrolidone (Table 9), the acylation of lactam anions with the exocyclic carbonyl of the growing acyllactam structure (i.e. exchange of monomer units) occurs faster than acylation with the cyclic carbonyl (propagation), viz. 

The consumption of one amine group in reaction (93) increases the acidity of the medium. In order to establish the equilibria (90) and (91), new amine groups and acyllactam structures are formed. As soon as at least one lactam molecule or lactam cation is involved in the disproportionation reaction (90), the sequence of disproportionation (90) and bimolecular aminolysis (93) results in the incorporation of one or two monomer units into the polymer molecule. The participation of this type of chain growth in cationic lactam polymerization, suggested by Doubravszky and Geleji [182—184], has been confirmed both for polymerization [185—188] as well as for model reactions [189, 190]. The heating of an equimolar mixture of acetylcaprolactam with cyclo-... 

In polymerizations initiated with salts of tertiary amines, the growth centres (i.e. primary amine groups and acyllactam structures) must be formed first, before propagation can start. Due to the low concentration of protonated lactam, the rate of polymerization is much lower than in polymerizations initiated with salts of lactams or primary and secondary amines (Fig. 21). 

As soon as polymer amide groups are formed, they can take part in both types of transacylation reactions (23) and (24). The disproportionation reactions involving polymer amide groups and/or anions produce acyllactam and diacylamine structures entering into the polymerization process... 

Decay of imide groups (acyllactam and diacylamine structures) during anionic caprolactam polymerization 1125]... 

The open chain structure (X) is formed in the condensation of diacylamine groups. The JV-acyllactam growth centres can undergo condensation at the cyclic as well as exocyclic methylene and carbonyl groups... 

However, even activated polymers contain basic (amine) groups resulting both from disproportionation and from side reactions [135,151], e.g., reaction (49). The end groups in anionic polymers are represented by primary amine, activator residue, acyllactam (both N- and a-) and carboxyl groups [134]. In addition, some basic groups other than primary amine are present [126]. A certain fraction of basic groups are ketimine structures resulting from intramolecular cyclization of a terminal amino ketone unit [124]... 

Whereas structure (113) prevails in cationic caprolactam polymers prepared at low temperature and short reaction periods, the fraction of amidine groups increases with temperature and time of polymerization. However, only small fractions of carboxyl groups were found in cationic polymers [180]. Only fractionated polymers contained equivalent amounts of basic and carboxylic groups which could also arise from hydrolysis of acyllactam groups [213]. 

The result Is an alternating block copolymer or A(BA) Instead of ABA which would occur If caprolactam polymerization occurred only from the acyllactam Initiating end groups. The structure Is presented more clearly In schematic. See page 147. 

The amount of caprolactam available for copolymerization Is equally divided between the active prepolymer ester and acyllactam groups so that the resulting nylon blocks are all the same molecular weight within the normal distribution curve for condensation polymers (i.e., Mw/Mn = 2/1). The elucidation of the alternating structure Is described more fully by J. E. Kurz. (14) Kurz used a method of selective degradation of the polyol blocks of nylon block copolymer and analyzed the resulting nylon residues. 

Simllcurly, acylamidinium ions result from dehydration of the tetrahedral intermediates formed during the reaction of acyllactams with cunmonium groups. Such groups arise inside the polymer.molecules two structures being possible, as shown in Equation 7. 

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