Lajos Avar

Polymer bound HALS—expectations and possibilities

This study confronts the traditional opinion on the physical aspects of the HALS efficiency with the available experimental reality. The results indicate that the generally accepted importance of additive migration may need to be reconsidered. Based on the experimental evidence, three empirical requirements for an effective stabiliser are formulated: high solubility, minimal diffusion and high homogeneity of distribution of active species. Chemical grafting of a low molecular stabiliser is suggested to meet the defined empirical requirements. The results achieved with polymer bound HALS (PBH) prepared by reactive processing technology confirm the expectations. The stabilisation efficiency of PBH significantly outperforms the conventional low molecular and oligomeric stabilisers.

Photo-physics and photo-chemistry of aromatic oxanilides used as polymer light stabilizers

Abstract Aromatic oxanilides, used as polymer light stabilizers, show a remarkably low photo-reactivity both in oxygen-free and in air-saturated solutions. Their photo-physical properties have been investigated by a combination of experimental and theoretical methods: photo-electron spectroscopy, electron energy loss spectroscopy, ultraviolet-visible and luminescence spectroscopy, laser flash photolysis and MINDO/3 calculations. In fluid solvents, and even in a polymer at room temperature, the lifetime of the excited singlet state is of the order of a few ps; this is ascribed tentatively to a reversible intramolecular proton transfer. Aromatic oxanilides protect photo-degradable polymers largely by their inner filter effect. Their role as quenchers of excited species is relatively unimportant and they have no action as radical scavengers, although they are not easily attacked by free radicals in solution.