Polyamide transamidation reaction

The molecular weight increases with increasing conversion. Regulation of the molecular weight can be achieved by adding small amounts of substances (e.g., benzoic acid) that can react with the polyamide chains by transamidation. Because of the transamidation reaction and hydrolysis of amide bonds, an equilibrium molecular-weight distribution is finally attained (see Sect. 4.1). 

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). 

H2N< C00H Polyamides 1. Amine (PA) + anhydride or acid (modifier) 2. Amine/carboxyl (PA) + epoxy (modifier) 3. Amine/carboxyl (PA) + isocyanate (modifier) 4. Carboxyl (PA) + oxazoline (modifier) 5. Carboxyl (PA) + nitrile (modifier) 6. Transamidation reactions (between PA and usually diamine type modifier)... 

Examples of copolymer formation by redistribution reactions in PA/PA blends are given in Table 5.5. In related work Liu and Donovan [1995] failed to find evidence for transamidation in PA-6 blends with an aromatic polyamide during molding and aimealing. 

Examples of copolymer formation by redistribution reactions (sometimes referred to as transreactions) in PA/PA blends are given in Table 5.8. In related work, Liu and Donovan (1995) failed to find evidence for transamidation in PA-6 blends with an aromatic polyamide during molding and annealing. Aspects of transreactions in PA/PA blends have been described in Eersels et al. (1999) and in portions of other chapters included in Fakirov (1999) (transreactions in condensation polymers). 

The reaction of an initiator with an amide group of the polymer chain, instead of that of the monomer, may result in the breaking of the macromolecule. Intermolecular transamidations can also modify the length of the polyamide chains and may generate cyclic stmctures. These exchange reactions result in a modification of the molar mass distribution. 

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... 

For instance, the synthesis of segmented poly(ether ester amide) copolymers with an aromatic polyamide block was attempted in N,N-dimethylacetamide solution, using a dihydroxy-terminated poly(oxyethylene) oligomer, >phenyl-enediamine, and isophthaloyl chloride [30]. Unfortunately, only low viscosity materials were obtained, probably due to side reactions involving the amide solvent (transamidation and acylation). 

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