Mechanism of accelerated photofading of thioether anthraquinone dyes in styrene butadiene resins

Abstract

SynopsisMany anthraquinone dyes fade in visible light up t o 100 times faster in styrene butadiene copolymers than in polyester resins or polystyrene. A mechanistic investigation of the photofading of 1,5-dihydroxy-2,6-diisobutyl-4-thiophenylanthraquinone has established that the dye sensitizes formation of singlet oxygen, a very reactive species, which attacks the double bonds in the styrene butadiene, resulting in extensive chain cleavage and peroxide formation. The major process is the oxidation of the polymer, and the dye fading is a minor process whereby the dye is apparently attacked by polymeric peroxides. The mechanism appears to be general for anthraquinone dyes, especially those with thioether, amino, hydroxy, or double-bond functionality. Unfortunately the fading is unaffected by most antioxidant stabilizers: the best result achieved was a doubling of half-life with 1 wt% Spinuvex A-36. This is still insufficient to give colored styrene butadiene copolymer resins the intrinsic dye stability available in other polymers, rendering styrene butadiene unsuitable for applications requiring high photostability of anthraquinone dyes.

Physico-Chemical Principles of Color Chemistry

“…They indicate that the process proceeds by hydrogen atom abstraction from the solvent and polymer to produce the leuco structure (36). In other work involving anthraquinone dyes in polymers, Paine et al 194 found that 1,5-dihydroxy-2,6-diisobutyl-4-thiophenylanthraquinones (37) faded up to 100 times faster in styrene-butadiene copolymer than in (35) c.l. characterized by mass (FAB) spectrometric-.…”