Polystyrene blend with poly , diffusion

The dependence of retention on thermodiffusion imparts an additional dimension to the thermal FFF separation that is not present in SEC. Although our understanding of thermodiffusion in solids and liquids is incomplete, certain aspects are clear. For example, thermodiffusion is very sensitive to the chemical composition of the polymer. As a result, thermal FFF is capable of separating components that differ in composition, even though they may have the same molecular-weight or diffusion coefficient. An example [4] of the separation of polystyrene and poly(methyl methacrylate) standards by thermal FFF is illustrated in Fig. 1. This separation cannot be accomplished with SEC because the diffusion coefficients (or hydrodynamic volumes) of the two materials are virtually identical. The ability of thermal FFF to separate materials by chemical composition has spurred additional research designed to increase our understanding of thermodiffusion [5], which, in turn, has led to the application of thermal FFF to polymer blends and copolymers [6]. 

Figure 26 8 Cyclic poly(oxyethylene) (as 30-crown-10) can be threaded and trapped onto linear polystyrene by polyrotaxanation. Diffusion-ordered NMR spectra of (a) poly[(styrene)-/o/flia-(30-crown-10)] (PS-roroxfl-30cl0, structure shown at top), and (b) blend of 30-crown-lO with PS-zo/oia-30c 10 (4/96, w/w) The polystyrene sports bulky ferf-butyl-containing end groups (labeled in spectra as t-Bu). The 30-crown-10 (3.7 ppm) in the polyrotaxane exhibits the same diffusion coefficient as the polystyrene (dashed horizontal line), which means it must be threaded. This is confirmed when some 30-crown-10 is added to the polyrotaxane and exhibits a separate, larger diffusion coefficient at the same chemical shift. (Reprinted with permission from T. Zhao and H.W. Beckham, Quantitative determination of threading in rotaxanated polymers by diffusion-ordered NMR spectroscopy, Macromolecules, 36, 4833 837, 2003. 2003 American Chemical Society.)...

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