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Handbook of Size Exclusion Chromatography and Related ...

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By measuring the scattered intensity at more than one angle, both the radius<br />

<strong>of</strong> gyration <strong>and</strong> the molecular weight can be determined for each elution volume.<br />

Jackson et al. (212) used multi-angle LS to determine the radius <strong>of</strong> gyration <strong>of</strong><br />

monodisperse <strong>and</strong> polydisperse polystyrenes. For the nearly monodisperse<br />

st<strong>and</strong>ards, measurements for radii greater than 10 nm were possible. For the<br />

polydisperse sample the lower limit was 18 nm. A similar LS detector was used to<br />

determine the relationship between radius <strong>of</strong> gyration <strong>and</strong> molecular weight for<br />

linear polyethylene (87), cross-linked polystyrene (213), <strong>and</strong> polyamic acid (214).<br />

Figure 14 shows a plot <strong>of</strong> Rg vs. Mw for a polyamic acid.<br />

The combination <strong>of</strong> a light-scattering detector <strong>and</strong> an on-line viscometer<br />

with SEC provides a method <strong>of</strong> directly measuring MWD <strong>and</strong> intrinsic viscosity<br />

distribution, as well as MWD, from universal calibration in a single experiment.<br />

Such a combined instrument has been used by Lesec <strong>and</strong> Volet (215,216) to<br />

characterize a range <strong>of</strong> linear <strong>and</strong> branched synthetic polymers. Tinl<strong>and</strong> <strong>and</strong> coworkers<br />

(217) used an SEC-viscometry-LS instrument to characterize xanthan <strong>and</strong><br />

dextran. Grubisic-Gallot et al. (66) added a second concentration detector to an<br />

SEC-viscometry-LS instrument to characterize block copolymers. Pang <strong>and</strong> Rudin<br />

(48) showed how each detector (light-scattering, viscometer, <strong>and</strong> DRI) provided<br />

Figure 14 Radius gyration Rg vs. weight-average molecular weight <strong>of</strong> a diethyl ester <strong>of</strong> a<br />

polyamic acid as determined using SEC with an on-line multi-angle laser light-scattering<br />

detector. The line through the data is the linear regression fit for molecular weight greater<br />

than 10 5 g/mol. (Adapted from Ref. 213, with permission from John Wiley <strong>and</strong> Sons, Inc.)<br />

© 2004 by Marcel Dekker, Inc.

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