Miscibility studies in blends of poly(methyl methacrylate) with poly(styren e-co-methacrylonitrile) using solid-state NMR and fluorescence spectroscopy

The miscibility in blends of poly(methyl methacrylate) (PMMA) with poly(styrene-co-methacrylonitrile) (SMAN) was examined by solid-state NMR and fluorescence spectroscopy. The value of the excimer/monomer fluorescence intensity (I(E)/I(M)) in the blends provides a sensitive measure of phase separation. A miscibility window in the blends of PMMA and SMAN containing about 30-65 mol % methacrylonitrile (MAN) monomer has been observed by fluorescence experiments. Measurements of T1pH by solid-state NMR have shown that blends containing 50:50 wt % PMMA blended with each of polystyrene, poly(methacrylonitrile), SMAN (MAN: 18.9 mol %), and SMAN (MAN: 87.6 mol %) are phase-separated. There is an intermolecular penetration between PMMA and copolymers in the blends of PMMA with SMAN (MAN: 43.8 mol %) and SMAN (MAN: 70.9 mol %) at a level of less than about 6 nm. However, the fluorescence data would indicate that intimate mixing does occur below this level. An analysis of the T1pH values for SMAN has indicated that the sequence distribution has an important effect on the interactions in the copolymer system

Riboflavin triplet quenchers inhibit lightstruck flavor formation in beer

We report that the primary photophysical event that leads to the formation of lightstruck flavor in beer exposed to visible light is the excitation of riboflavin to its triplet state followed by electron transfer from iso-alpha-acids. This conclusion is based on laser flash photolysis measurements that quantitatively characterize the action of various triplet state quenchers combined with sensory analysis. Our findings rationalize the effect of triplet quenching on the lightstruck reaction and provide commercially acceptable methods of control. Beer has an inherent ability to quench the riboflavin triplet, and hence, provide some protection against lightstruck character formation. Now we show how this information could be used to stabilize beer. The concentrations of the naturally occurring quenchers, catechin and tryptophan, required to quench the riboflavin triplet have been determined. The effect of ascorbic acid, a known riboflavin triplet quencher and powerful antioxidant, was also examined. Sensory analysis showed that when dosed at high enough concentrations, riboflavin triplet state quenchers are able to inhibit the formation of lightstruck character