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Handbook of Size Exclusion Chromatography and Related ...

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As pointed out earlier, rubber must first be dissolved in SEC solvent when<br />

SEC analysis is attempted. Almost all final rubber products, however, are<br />

produced by vulcanization, in which raw rubbers tend to become completely<br />

insoluble. Therefore, SEC <strong>of</strong> rubbers is limited to raw rubbers only. This criterion,<br />

however, is not obeyed for SEC <strong>of</strong> low-molecular-weight compounds in<br />

vulcanized rubbers. Vulcanized rubbers contain many additives, such as curatives,<br />

antioxidants, <strong>and</strong> modifiers. These additives can be easily analyzed by SEC if their<br />

forms are soluble in SEC solvents, as demonstrated by Zimbo et al. (34) for the<br />

SEC analysis <strong>of</strong> the extender oil bloom on EPDM (terpolymer <strong>of</strong> ethylene,<br />

propylene, <strong>and</strong> a diene) vulcanizates.<br />

3 GENERAL REMARKS<br />

To manifest the particular property <strong>of</strong> rubber, high elasticity, rubbers have high<br />

molecular weights with a broad molecular weight distribution compared with other<br />

polymeric materials. This is seen typically in the molecular weight distribution<br />

curve for natural rubber (NR), shown in Fig. 1. Synthetic commercial rubbers were<br />

initially produced after natural rubber, <strong>and</strong> their molecular weight distributions<br />

were also almost the same as that <strong>of</strong> natural rubber. Therefore, the SEC<br />

characteristics <strong>of</strong> the various rubbers are considered together.<br />

The convenience <strong>of</strong> SEC for the determination <strong>of</strong> molecular weight data for<br />

a wide variety <strong>of</strong> synthetic rubbers was appreciated early after the introduction <strong>of</strong><br />

Figure 1 Chromatograms <strong>of</strong> Natsyn 400 <strong>and</strong> natural rubber. Instrument: Waters Model<br />

200. Column: 10 6 ,10 5 ,5 10 4 ,10 3 A ˚ porosities. Mobile phase: THF (0.05% wt/vol<br />

antioxidant). Flow rate: 0.91, 0.95mL/min. Temperature: 358C. (From Ref. 8.)<br />

© 2004 by Marcel Dekker, Inc.

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