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Handbook of Size Exclusion Chromatography and Related ...

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exclusion chromatography with low-angle laser light scattering (SEC/LALLS)<br />

<strong>and</strong> SEC with universal calibration (Table 8). The molecular weights (relative to<br />

polyethylene oxide st<strong>and</strong>ards) <strong>of</strong> nonionic copolymers <strong>of</strong> vinyl pyrrolidone <strong>and</strong><br />

vinyl acetate, anonionic terpolymer <strong>of</strong> vinyl pyrrolidone, dimethylaminoethyl<br />

methacrylate,<strong>and</strong>vinylcaprolactam,<strong>and</strong>anioniccopolymers<strong>of</strong>vinylpyrrolidone<br />

<strong>and</strong> acrylic acid were also reported in 1991 (6) by Wu et al. (Tables 6<strong>and</strong> 7).<br />

3 MOLECULAR WEIGHT DISTRIBUTION OF VP-BASED<br />

POLYMERS BY SIZE EXCLUSION CHROMATOGRAPHY<br />

Many important properties <strong>of</strong> polymers depend not only on molecular weight but<br />

also on molecular weight distribution. For example, both viscosity <strong>and</strong> its<br />

dependence on the shear rate <strong>of</strong> polymer melt <strong>and</strong> concentrated polymer solution are<br />

dependent on molecular weight distribution. SEC is the most practical <strong>and</strong> the best<br />

method for determining the molecular weight distribution <strong>of</strong> a polymer without going<br />

through the tedious classic fractionation procedure using nonsolvent precipitation.<br />

3.1 SEC <strong>of</strong> PVP: Historical Review<br />

The SEC <strong>of</strong> PVP is not straightforward because <strong>of</strong> the polar nature <strong>of</strong> the polymer.<br />

Various interactions between PVP <strong>and</strong> columns, such as adsorption, partition, <strong>and</strong><br />

electrostatic interactions, must be eliminated by prudent choice <strong>of</strong> column <strong>and</strong><br />

mobile phase to obtain true separation by size with 100% recovery <strong>and</strong> compliance<br />

with universal calibration.<br />

The SEC behavior <strong>of</strong> PVP has been <strong>of</strong> interest to many researchers. In the<br />

10-year period from 1975 to 1984, seven papers, using seven different kinds <strong>of</strong><br />

columns with various surface modifications <strong>and</strong> in both aqueous <strong>and</strong> nonaqueous<br />

mobile phases with <strong>and</strong> without modifiers <strong>and</strong> salts, were reported for the SEC <strong>of</strong><br />

PVP with different degrees <strong>of</strong> success. Some <strong>of</strong> the columns used are<br />

commercially available; others are specially made.<br />

Belenkii et al. reported in 1975 (7) the SEC <strong>of</strong> PVP with unspecified<br />

molecular weight using Pharmacia Sephadex G-75 <strong>and</strong> G-100 columns <strong>and</strong> a 0.3%<br />

sodium chloride solution as the mobile phase. Deviations from universal<br />

calibration behavior were noticed from PVP, dextran, polyethylene oxide (PEO),<br />

<strong>and</strong> polyvinyl alcohol. With the development <strong>of</strong> the important semirigid polymer<br />

gel, Toyo Soda TSK-PW columns for water-soluble polymers, Hashimoto et al.<br />

reported in 1978 (8) the SEC <strong>of</strong> PVP K-30 <strong>and</strong> K-90 using TSK-PW 3000 <strong>and</strong> two<br />

5000 columns an 0.08 M Tris–HCl buffer (pH ¼ 7.94) as mobile phase <strong>and</strong> PEO<br />

<strong>and</strong> dextran as calibration st<strong>and</strong>ards.<br />

By using an E. Merck LiChrospher SI300 column, modified with an amide<br />

group chemically bonded to the surface, Englehardt <strong>and</strong> Mathes reported in 1979<br />

(9) the SEC <strong>of</strong> PVP with molecular weights from 10,000 to 360,000 AMU. A 0.1 M<br />

© 2004 by Marcel Dekker, Inc.

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