David M. Rice

Miscibility of syndiotactic polystyrene/poly (vinyl methyl ether) blends

Abstract The dependence of miscibility on blend composition and temperature for syndiotactic polystyrene/poly(vinyl methyl ether) (SPS/PVME) blends, was investigated by solid state n.m.r. spectroscopy and d.s.c. and compared with that of the blend containing atactic polystyrene (APS). The temperature dependence of 13 C cross polarization/magic angle spinning intensities for the resonance of SPS/PVME blends indicates that these blends are phase separated, whereas for the APS/PVME blends, there is evidence of extensive mixing. These results are supported by the presence of one and two glass transition temperatures for the SPS/PVME and APS/PVME blends, respectively, on the d.s.c. thermograms.

Investigation of H2SO4-doped, ring-deuterated poly(p-phenylene vinylene) using solid state 2H quadrupole echo n.m.r. spectroscopy

Abstract Ring-deuterated poly( p -phenylene vinylene) has been doped with concentrated sulphuric acid and examined with 2 H quadrupole echo nuclear magnetic resonance spectroscopy. Doping is observed to change the relative population of fast versus slow flipping p -phenylene rings. This relationship has been investigated over a range of temperatures. Modelling this system as a two-site chemical exchange shows that the change in the relative populations of fast versus slow ‘flippers’ corresponds to an increase in the activation energy for the 180° ring flip. The width of the distribution of flip rates is also observed to increase upon doping. At elevated temperatures the samples studied undergo a significant loss of mass which corresponds to a loss of dopant. The chemistry of this process is examined.

A multitechnique investigation of sodium-doped poly(p-phenylene vinylene)

Abstract Dopant uptake in sodium-doped poly( p -phenylene vinylene) (PPV) has been measured, and e.s.r. spectroscopy has been used to follow the changes in unpaired spin concentration as the doping reaction proceeds. 2 H n.m.r. line shapes of sodium-doped, ring-deuterated PPV (PPV-d 4 ) have also been studied to observe the effects of doping. They contain two distinct components, one of which is attributed to hydride formation. The overall pattern is insensitive to temperature changes.

Intracellular pH Does Not Change during Phytochrome-Mediated Spore Germination in Onoclea

Abstract Calcium ions may act as a “second messenger” in phytochrome-mediated spore germination in Onoclea sensibilis L. In this study we determine whether changes in intracellular pH also contribute to the signal transduction chain. Using 31 P nuclear magnetic resonance spectrometry, in which we are able to resolve changes as small as 0.2 pH units, we fail to observe any change in pH associated with red light irradiation. In addition artificially inducing an intracellular change in pH of greater than 1 pH unit (5.8-7.2) has no effect on germination. These data indicate that a sustained increase in intracellular pH does not contribute to the signal transduction chain in phytochrome-mediated fern spore germination.

Preparation of poly(p-phenylene vinylene) deuterium labelled in the vinylene positions

Abstract The preparation of poly( p -phenylene vinylene) specifically labelled at the vinylene positions is herein described. The extent of deuteration is estimated by i.r. spectroscopy, and the mechanism of hydrogen/deuterium exchange during the polymerization process is discussed.