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Handbook of Size Exclusion Chromatography and Related ...

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Table 1 Measurement <strong>of</strong> Molecular Weight Distribution by SEC-Viscometry: Selected<br />

Applications<br />

Macromolecule References<br />

Homopolymers<br />

Polystyrene 34,44–46<br />

Polymethyl methacrylate 34,45–47<br />

Polyolefins 48<br />

Polyvinyl chloride 34,45<br />

Polyvinyl acetate 45<br />

Polyvinyl alcohol 49<br />

Polyallylamine 50<br />

Polyethylene oxide 51<br />

Polyamides 52,53<br />

Polyphenylene sulfide 54<br />

Copolymers<br />

Ethylene-vinyl acetate 55<br />

Natural polymers <strong>and</strong> derivatives<br />

Lignin 56–58<br />

Cotton 59<br />

Starch 60<br />

Pectin 61,62<br />

Biopolymers<br />

Proteins 63,64<br />

strains by determining the relationship between molecular composition <strong>and</strong> fiber<br />

strength <strong>and</strong> length.<br />

4.1.2 Copolymer Molecular Weight Distribution<br />

The difficulty with copolymer analysis is in the measurement <strong>of</strong> the concentration<br />

<strong>of</strong> each elution volume. On-line viscometers measure the correct specific viscosity<br />

for copolymers. If universal calibration holds, the problem with which we are<br />

faced is converting the specific viscosity into an intrinsic viscosity. Only if there is<br />

no compositional drift with elution volume does the output from a refractometer or<br />

UV detector correspond directly to concentration. If there are compositional<br />

changes, then the signal reflects these changes through changes in the detector<br />

response factor. If the composition changes with molecular weight, then a second<br />

detector can be used that is sensitive to only one component <strong>of</strong> the copolymer (65).<br />

This method was used recently by Grubisic-Gallot et al. (66) to characterize<br />

polystyrene-b-methyl methacrylate block copolymers. A UV detector set at<br />

262 nm, at which wavelength polymethyl methacrylate does not absorb, was used<br />

© 2004 by Marcel Dekker, Inc.

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