Polystyrene small-molecule rotation

Gisser and Ediger(41) studied solvent and solute rotation with C and nuclear magnetic resonance. The selectivity of NMR allows separate measurement of reorientation times for multiple components of a mixture. Dilute polystyrene, polyisoprene, and polybutadiene were found to retard the rotational diffusion of the toluene solvent, polystyrene being modestly more effective as a retardant. Solvent Tr depends exponentially on polymer c, at least up to 90 g/1 of polymer. Gisser and Ediger also examined the small-molecule mixture chloronaphthalene ... 

Chapter 5 considers translation and rotation by solvent molecules in small-molecule liquids and polymer solutions. Correlations between solution properties are already more complex than might have been expected. At small rj, the diffusion coefficient and equivalent conductance of small-molecule probes in simple liquids scale as At larger rj, D and A are instead The boundary between small and large t] seen in the literature is uniformly near 5 cP. It is unclear why this particular value of r should not be system-specific. In contrast to smaU-molecule probes, mesoscopic probes such as polystyrene latex spheres in potentially highly viscous mixed solvents such as water glycerol retain D T/ri behavior over three or more orders of magnitude in rj. 

Fig. 8.1. Detail of a large polystyrene molecule as it might appear in a good solvent such as toluene. Each sphere represents a carbon atom and one or two small hydrogen atoms attached to it. The chemical bonds are superimposed on one repeating unit or monomer, and on a section of the chain backbone. The backbone bonds may rotate freely. A few successive backbone repeat units...

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