Tertiary phosphine complexes of nickel(II) thiocyanate: an evaluation of the photostabilisation of polystyrene

Polystyrene films have been prepared incorporating zinc stearate and nickel(II) thiocyanate complexes of methyldiphenyl- and alkenyldiphenyl-phosphines (alkenyl=vinyl, allyl, but-3-enyl, pent-4-enyl). Investigation of the thermal and fluorescence properties of the nickel complexes indicates high thermal stability and minimal photochemical activity. Polymer films containing the zinc and nickel complexes were photodegraded under artificial conditions and referenced to a similarly exposed nickel-free standard. The degradation of films containing nickel additives and the nickel-free standard was assessed using diffuse reflectance IR spectroscopy, CIELab colour space and 31P{1H} NMR. Within the polymer films nickel complexes do not degrade at a significantly greater rate than the polymer matrix, and whilst those containing vinyl, but-3-enyl and pent-4-enyl functions appear passive (displaying neither photosensitisation nor photostabilisation), methyl and allyl substituted complexes do offer significant stabilisation. Phosphine oxide species are identified by 31P{1H} NMR as the principal decomposition products, suggesting that peroxide oxidation of co-ordinated phosphines may represent the principal mode of photostabilisation. Assessments of colour space fastness on exposure to aqueous, acidic and alkaline media were made. These indicate comparable decomposition of nickel(II) thiocyanate and zinc stearate complexes in all three environments, suggesting that hydrolytic processes predominate in complex decomposition.