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Handbook of Size Exclusion Chromatography and Related ...

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Table 5 Mark–Houwink Viscometric Constant for Rubbers Used for SEC<br />

Polymer Solvent Temperature (8C) K 10 4 a Reference<br />

Natural rubber THF 25 1.09 0.79 72<br />

Polybutadiene THF 25 2.36 0.75 72<br />

Polyisoprene THF 25 1.77 0.735 72<br />

SBR (28% styrene) THF 25 4.51 0.693 72<br />

Polybutadiene ODCB 135 2.7 0.746 72<br />

Polydimethylsiloxane ODCB 135 3.83 0.57 72<br />

CHCl3 30 0.54 0.77 72<br />

Polyaryloxyphosphazene THF 30 0.0119 0.649 30<br />

distribution as well as the SEC system, including columns <strong>and</strong> instrumentation.<br />

Although the fingerprinting method is qualitative, it is the most frequently used<br />

method for the design <strong>of</strong> syntheses <strong>of</strong> new rubber polymers. SEC chromatograms<br />

indicate polymerization recipes <strong>and</strong> polymerization conditions (47,50,52).<br />

3.4 SEC <strong>of</strong> Molecular Branching<br />

Both natural rubber (Hevea) <strong>and</strong> synthetic rubbers have molecular chain<br />

branching. The presence <strong>of</strong> branched molecules affects the SEC behavior to a<br />

great extent, because abranched molecule has asmaller hydrodynamic volume<br />

than alinear chain molecule <strong>of</strong> the same molecular weight <strong>and</strong> is eluted later.<br />

Therefore, when branched molecules are present, an erroneous molecular weight<br />

distribution curve results by analyzing the SEC curve as if there are only linear<br />

molecules. Subramaniam (8) has shown an example in the SEC analysis <strong>of</strong> NR.<br />

ManymodernSECsystemsincludeLALLS.Asdescribedearlier,thisgives<br />

information about both the molecular weight distribution <strong>and</strong> the extent <strong>of</strong> chain<br />

branching in the same SEC analysis time. It is convenient for simultaneous<br />

determination <strong>of</strong> chain branching <strong>and</strong> molecular weight distribution. Even when<br />

LALLS is not used, acombination <strong>of</strong> SEC <strong>and</strong> viscometric measurements can<br />

estimate chain branching using the universal hydrodynamic calibration method<br />

(63). Fuller <strong>and</strong> Fulton (3) studied the relation between molecular branching <strong>and</strong><br />

the mechanical behavior <strong>of</strong> NR.<br />

3.5 SEC <strong>of</strong> Copolymer Rubbers <strong>and</strong> Blends<br />

As can be seen in Table 1, several rubbers have acopolymer structure. The<br />

physical properties <strong>of</strong> the copolymers are affected not only by the molecular<br />

weight distribution but also by the compositional distribution. Therefore, it is<br />

desirable to know the compositional distribution in addition to the molecular<br />

© 2004 by Marcel Dekker, Inc.

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