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Handbook of Size Exclusion Chromatography and Related ...

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Figure 7 Effects <strong>of</strong> fluctuating reactor conditions on the steady state <strong>of</strong> Mw <strong>and</strong> f . (From<br />

Ref. 34.)<br />

fluctuations in the reactor cause immediate fluctuations in both f <strong>and</strong> Mw; asT<br />

decreases conversion decreases <strong>and</strong> Mw increases. After this, the concentration <strong>of</strong><br />

initiator was made to fluctuate, leading to corresponding fluctuations in f <strong>and</strong> Mw,in<br />

the sense expected. Finally, mixing fluctuations were produced by changing agitation<br />

speed, <strong>and</strong> ceasing to stir altogether. The latter had a drastic effect on both f <strong>and</strong> Mw.<br />

2.1.4 Controlled Radical Polymerization (CRP)<br />

CRP combines the control performance <strong>of</strong> living polymerization with the robust,<br />

economical aspects <strong>of</strong> free radical polymerization. Several types <strong>of</strong> CRP exist,<br />

most <strong>of</strong> which are based on a reversible combination between the growing radicals<br />

P † , <strong>and</strong> a molecular species X*, shown in Scheme 1. The majority <strong>of</strong> initiated<br />

chains are normally “dormant” in the P–X form, since, typically the equilibrium<br />

constant Keq ¼ kact=kdeact is much smaller than one, <strong>and</strong> those chains that are<br />

active add monomer M with a rate constant kp, or terminate with a much smaller<br />

probability via rate constant kt, until they again associate with X* <strong>and</strong> fall dormant.<br />

© 2004 by Marcel Dekker, Inc.

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