Diffusion coefficients, radii of gyration, and second virial coefficients of short polystyrene chains have been measured by dynamic light scattering, small-angle neutron scattering, and static light scattering. Deviations from the established exponential laws at high molecular weights are observed in all cases. The hydrodynamic behavior can equally well be described by Kirkwood's diffusion equation, if the free draining term is properly taken into account, and by the Yamakawa-Fujii theory of cylindrical wormlike chains. The enhanced increase of A2 for short chains is caused by the inherent chain stiffness. Satisfactory agreement of the Stockmayer-Yamakawa theory with experiment is obtained if a 45% higher Kuhn length is assumed in toluene at 20 °C than in cyclohexane at 34.5 °C.
A modified photon correlation spectrometer that allows the simultaneous recording of dynamic and static light scattering is described. Details for a precise alignment are given. The utility of the equipment is demonstrated with four well-characterized polystyrene samples and two polystyrene latices. Excellent agreement with literature values is obtained for the linear, monodisperse polystyrene samples. The apparent diffusion coefficient, Z)app, of the large latex particle (481 nm) exhibits no angular dependence up to an angle of 120°. At larger angles a drastic drop of Z),™ is observed, which is shown to be caused by 2% reflection of the primary beam at the solution-glass boundary and at the refractive index matching bath-air boundary. For the smaller latex (91 nm) the back-scattering has a somewhat different influence on Z)app, which is almost negligible.
Starting with properly protected sugar alcohols, bioerodible polycarbonates having pendant hydroxy substituents at the main polymer chain (poly(hydroxyalkylene carbonatéis, (PHAC's)) have been synthesized for the first time. The PHAC's are the first examples of water-soluble polycarbonates. Due to water solubility, these polyols may replace PEG's in some applications. On derivatization of the hydroxy groups as a carboxylic or carbonic acid ester or as an ortho ester, additional bioerodible polycarbonates having quite different solubility and degradation properties were available.
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