Nile Red was used as a solvatochromic probe to measure the solvent strength of 85 pure liquids and the results were compared to solvent strength scales from the better known Relchardt's E^) and E^d yes. Nile Red Is also soluble in some pure supercritical fluids and In polar mixtures of supercritical fluids and modifiers. The solvent strength of mixtures of organic modifiers In C02, Freon-13, and Freon-23 was measured as a function of modifier concentration with Nile Red and other solvatochromic dyes. Nile Red exhibits large shifts In the wavelength of Its absorption maximum allowing subtle changes In solvent strength with fluid composition to be quantified, and It Is stable In very strong acids. Relative scales of solvent strength comparing different modifiers added to C02 are presented and compared to a wide range of normal liquids.

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Derivatives of 2,2,5,5-tetraalkylimidazolidin-4-one-1-oxyl have been found to offer significant advantages over many of the nitroxides previously employed in nitroxide-mediated polymerization:  homopolymers [e.g., polystyrene and poly(alkyl acrylate)], statistical copolymers [e.g., poly(styrene-co-acrylonitrile)], and block copolymers [e.g., poly(4-methylstyrene)-block-polystyrene and poly(n-butyl acrylate)-block-polystyrene] can be synthesized with controlled molecular weight, narrow molecular weight distribution, and defined end group functionality. The effect of substituents α to the nitroxide nitrogen and at the transannular nitrogen on the outcome of polymerization is explored. Appropriate selection of these substituents provides polymers of lower polydispersities than, for example, 2,2,6,6-tetramethylpiperidin-2-oxyl and derivatives. The nitroxides are synthesized from readily available precursors by a simple experimental route. Moreover, they are subject to fewer side reactions. In particular, disproportionation between the propagating radical with nitroxide appears to be of lesser significance.