Analysis of the fluorescent and phosphorescent species in nylon-6,6 in relation to aldol condensation products of cyclopentanone

Abstract

Fluorescence analysis of nylon-6,6 polymer indicates the presence of a number of chromophoric species. One of the main species has excitation maximum at 290 nm with a corresponding emission maximum at 326 nm and is extractable from the polymer by 2-propanol; another has an excitation maximum at 340 nm and corresponding emission maximum at 390 and 420 nm and is virtually non-extractable. The latter, as established by other workers, is associated with the presence of α-ketoimide structures formed by thermal oxidation of the molecular backbone of the polymer. The former, after isolation from cyclic nylon monomer using silica TLC, is shown to possess two excitation maxima at 228 and 284 nm and regenerates on exposure of the extracted polymer to pure oxygen and is attributed to a slow ambient oxidation process and not absorption of naphthalene from the “urban atmosphere”. This is confirmed by hydroperoxide analysis of the polymer before and after regeneration. Despite large scale extraction procedures (∼ 2 kg polymer), only trace amounts of the fluorescent species could be isolated after TLC analysis. However, using GC-mass spectrometry interfaced to a computer library (courtesy of ICI Organics Division plc, Manchester) the presence of cyclic enone dimer and dienone trimer of cyclopentanone amongst other products was confirmed in the 2-propanol extract. The phosphorescence emission from the polymer is shown to correspond to a complex mixture of these products and is little affected by 2-propanol extraction. Both the fluorescent and phosphorescent species in nylon-6,6 polymer are shown to originate from aldol condensation products of cyclopentanone. This is confirmed through a detailed luminescence/GC-mass spectrometry analysis of the products of the latter process. Feasible mechanisms, based on earlier nylon oxidation studies, are discussed.