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Handbook of Size Exclusion Chromatography and Related ...

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Figure3showsAAmconversionvs.timeforthereactioninFig.2,aswellas<br />

several others, where the ratio <strong>of</strong> AAm to initiator was varied. In all cases the<br />

conversion is fit fairly well by afirst order (exponential) fit. As the amount <strong>of</strong><br />

initiator decreases <strong>and</strong> conversion slows, however, the fit is less good, <strong>and</strong> it was<br />

demonstrated in Ref. 33 that the deviations from the ideal free radical<br />

polymerization paradigm were due to impurity <strong>and</strong> cage effects.<br />

Figure 4 shows M w vs. conversion for several AAm polymerization<br />

experiments. The QSSA above predicts that Mw at any value <strong>of</strong> monomer<br />

conversion f , should obey<br />

Mw( f ) ¼ Mw(0) 1<br />

f<br />

2<br />

(11)<br />

Both the linearity <strong>and</strong> ratio <strong>of</strong> Mw(0)=Mw(1) ¼ 2=1 are seen in Fig. 4. Deviations<br />

at early values <strong>of</strong> conversion (up to 5–15%) before the straight line, ideal regime is<br />

reached, are also due to impurity <strong>and</strong> cage effects. The solid circles in Fig. 4<br />

Figure 3 Monomer conversion during the free radical polymerization, from data in Fig. 2<br />

<strong>and</strong> other, similar reactions, where the ratio <strong>of</strong> AAm to persulfate initiator varied. At high<br />

initiator concentrations the conversion is almost perfectly first order (exponential), with<br />

deviations from first order becoming more apparent as initiator concentration decreases.<br />

(From Ref. 33.)<br />

© 2004 by Marcel Dekker, Inc.

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