Abstract
The photo-stabilisation of nylon 6,6 polymer by various hindered piperidine stabilisers has been examined by viscosity number, ultra-violet absorption and luminescence spectroscopy. Photo-oxidation of the polymer is inhibited to varying degrees depending upon the structure of the molecule and its ability to react with terminal carboxylic acid groups. Thus, the monomeric stabilisers impart more stability than the larger polymeric types and this is associated with improved solubility and compatibility of the former types in the polar and highly crystalline nylon 6,6 polymer. Reaction of terminal carboxylic acid groups with 2,2,6,6-tetramethylpiperidin-4-ol (TMP) markedly improves the photo-stability of the polymer and this is confirmed by extraction experiments with 2-propanol. In all cases changes in viscosity number of the polymer films correlate closely with changes in their ultra-violet absorption at 294 nm during irradiation. Analysis of the polymers initially by fluorescence and phosphorescence spectroscopy indicates some degree of correlation between polymer stability and the concentration of cyclic α,β-unsaturated carbonyl oxidation products absorbing and emitting light with wavelength maxima at 297 and 330 nm, respectively. These results are compared and discussed with regard to earlier work on the stability of nylon 6,6 polymers with high concentrations of terminal amine groups.
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