PHOTOINITIATOR PROPERTIES OF 2-SUBSTITUTED AMIDO AND ACRYLOXYANTHRAQUINONES

The photophysical and photoinduced polymerization activities of 2-acry lamido, 2(2-ethylhexyl)amido and 2-acryloxyanthraquinones have been de termined in solution media. The photoinduced polymerization activities of the two amido derivatives in methyl methacrylate (MMA) are greater than that of the acryloxy derivative. This is consistent with two for mer derivatives exhibiting longest wavelength absorption maxima some 5 0 nm red shifted from that of the 2-acryloxy derivative. The shorter w avelength absorption band of the latter exhibits a small blue shift wi th increasing solvent polarity indicative of an n pi configuration. A ll three compounds appear to show little evidence of any charge-transf er interaction with the solvent environment. Fluorescence and phosphor escence analysis of the three compounds confirm the existence of low l ying n pi excited states and rapid intersystem crossing to the next l owest lying triplet n pi excited states. Photoinduced polymerization of MMA monomer gave polymers with a higher molecular weight for the tw o acrylated derivatives. Second derivative u.v. analysis showed the an thraquinone chromophore for each of the molecules to be incorporated i n the polymer (PMMA) to the same extent indicating the absence of any copolymerization with the acrylated groups of the anthraquinones. Inco rporation of the anthraquinone through the semiquinone radicals may be an important mechanism in all cases. In the case of the 2-(2-ethylhex ylamido) anthraquinone, alkylamido radicals formed by inter or intra-m olecular hydrogen atom abstraction may be formed which can behave as i nitiators of the polymerization. The role of the triplet state in phot oinduced polymerization was confirmed by the observation of a strong i nhibiting effect in air. Furthermore, the use of both a radical trap ( nitroxyl free radical) and an electron trap (tetracyanoethylene) also strongly inhibited the polymerization of MMA indicating the role of bo th radical and electron transfer processes in the photopolymerization reaction.