Phosphorus-containing oligoamides obtained by a novel one-pot degradation of polyamide-6

This paper describes a novel strategy for the recycling of polyamide materials and their transformation into functional reactive oligomers with new properties. The method is illustrated by the heating of polyamide-6 (20,000 Da) in the presence of diesters of the phosphonic acid, (RO)₂P(O)H, where R could be -CH₃, -C₂H₅ or -C₆H₅. It is found that the reaction proceeds in several parallel processes: (i) phosphorylation of the amide group by the alkyl esters of the phosphonic acids and (ii) degradation of the main chain through an exchange reaction between the amide and phosphonic acid ester groups. Alternatively the depolymerization could be induced via a radical reaction with the participation of the polyamide moieties and the P-H group. The proceeding of the abovementioned reactions and the structure of the phosphorus-containing oligoamides are confirmed by ³¹P, ¹H and ¹³C NMR spectroscopy. Their molecular weights are determined by size exclusion chromatography.