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Handbook of Size Exclusion Chromatography and Related ...

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condition, as is explained in this chapter. The injected solution is concentrated,<br />

as is the eluent. Therefore, it is easy to recover solid polymer in each <strong>of</strong> the<br />

fractions. With minimal consumption <strong>of</strong> <strong>of</strong>ten hazardous organic solvents,<br />

HOPC is an environmentally friendly separation method for a wide variety <strong>of</strong><br />

polymers.<br />

The first half <strong>of</strong> this chapter explains the separation principle <strong>of</strong> HOPC in a<br />

good solvent condition. A couple <strong>of</strong> examples <strong>of</strong> separation are given. The second<br />

half focuses on recent extension <strong>of</strong> HOPC into theta solvent condition. The latter<br />

solvent allows a superior resolution <strong>and</strong> a greater processing capacity compared<br />

with the good solvent. In particular, use <strong>of</strong> weakly adsorbing porous packing<br />

makes it possible to produce narrow-distribution fractions from early to late eluent,<br />

yet rejuvenating the column at the end <strong>of</strong> each batch.<br />

2 SEPARATION PRINCIPLE: HOPC IN A GOOD SOLVENT<br />

The separation in HOPC is based on partitioning <strong>of</strong> a concentrated solution <strong>of</strong><br />

polymer between a pore space (stationary phase) <strong>and</strong> a surrounding unconfined<br />

space (mobile phase). When the polymer is monodisperse <strong>and</strong> the solution is<br />

dilute (much lower than the overlap concentration c*), the partition coefficient<br />

K is a sharply decreasing function <strong>of</strong> MW <strong>of</strong> the polymer (dashed line in Fig. 1).<br />

This principle is widely used in size exclusion chromatography (SEC). As in<br />

Figure 1 Partition coefficient K is schematically drawn as a function <strong>of</strong> MW in a<br />

logarithmic scale. Dashed lines, low concentrations; dash-dotted lines, higher<br />

concentrations; monodisperse polymer, solid lines; higher concentrations, polydisperse<br />

polymer.<br />

© 2004 by Marcel Dekker, Inc.

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