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Handbook of Size Exclusion Chromatography and Related ...

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5<br />

Characterization <strong>of</strong><br />

Copolymers by<br />

<strong>Size</strong> <strong>Exclusion</strong><br />

<strong>Chromatography</strong><br />

Gregorio R. Meira <strong>and</strong> Jorge R. Vega<br />

INTEC (Universidad Nacional del Litoral <strong>and</strong> CONICET)<br />

Santa Fe, Argentina<br />

1 INTRODUCTION<br />

Copolymers are characterized by a chemical composition distribution (CCD) that<br />

is represented by the mass fraction <strong>of</strong> molecules <strong>of</strong> a given copolymer composition<br />

vs. the copolymer composition. This characteristic considerably complicates<br />

the determination <strong>of</strong> the molecular weight distribution (MWD) <strong>of</strong> a copolymer by<br />

size exclusion chromatography (SEC) (1–7). However, there are two situations<br />

where copolymers can be almost treated as homopolymers from the point <strong>of</strong> view<br />

<strong>of</strong> the MWD estimation: (1) when the CCD is very narrow, or (2) (more generally)<br />

when the average composition does not change with hydrodynamic volume.<br />

Copolymers with narrow CCDs are in general desirable from the point <strong>of</strong> view <strong>of</strong><br />

their end properties, <strong>and</strong> a control <strong>of</strong> the chemical composition along the<br />

copolymerization may be necessary for producing narrow CCDs. More normally,<br />

however, the average composition changes along the polymerization, <strong>and</strong> also<br />

© 2004 by Marcel Dekker, Inc.

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