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Handbook of Size Exclusion Chromatography and Related ...

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evolution, can be carried out on the polymer, while evolution in colloid particle<br />

density is measured.<br />

HTDSLS has been demonstrated in contexts where large amounts <strong>of</strong><br />

colloidal contaminant were added to apolymer solution, <strong>and</strong> afull Zimm-style<br />

analysis <strong>of</strong> the polymer was recovered, <strong>and</strong> in acase where the evolution <strong>of</strong><br />

Escherichia coli bacteria in apopulation <strong>of</strong> water-soluble polymer (polyvinyl<br />

pyrrolidone, or PVP) was monitored, while the PVP itself was characterized.<br />

Figure1showsdatatakenatascatteringangle<strong>of</strong>908fromco-existingE.coli<strong>and</strong><br />

PVP populations, adapted from Ref. 31. Each spike corresponds to a single E. coli<br />

bacterium passing through the scattering volume, <strong>and</strong> the increasing spike density<br />

shows the increase in time <strong>of</strong> the E. coli population density. The E. coli density is<br />

shown in the top inset graph. The baseline due to PVP is recoverable at each<br />

instant, <strong>and</strong> yields the characterization in terms <strong>of</strong> Kc=I shown in the lower inset<br />

graph.<br />

HTDSLS can be incorporated as an integral part <strong>of</strong> light-scattering detection<br />

in the many cases where colloids co-exist with polymers.<br />

2 ON-LINE MONITORING OF POLYMER PROCESSES<br />

2.1 Automatic Continuous On-line Monitoring <strong>of</strong><br />

Polymerization Reactions (ACOMP)<br />

The ability to monitor conversion <strong>and</strong> the evolution <strong>of</strong> mass <strong>and</strong> composition<br />

distributions during polymerization reactions is important in three broad areas.<br />

First, polymer scientists working on new material development can obtain detailed,<br />

quantitative information on kinetics <strong>and</strong> mechanisms that can accelerate the<br />

process <strong>of</strong> discovery <strong>and</strong> underst<strong>and</strong>ing. Secondly, chemists <strong>and</strong> engineers seeking<br />

to optimize reaction conditions can immediately assess the effects <strong>of</strong> changing<br />

initiators, catalysts, temperature, concentration, solvents, <strong>and</strong> so on. Finally, it is<br />

expected that ACOMP will provide a process analytical approach to on-line<br />

control <strong>of</strong> polymerization reactors. This should lead to considerable increases in<br />

efficiency <strong>and</strong> product quality, <strong>and</strong> lead to important savings in terms <strong>of</strong><br />

nonrenewable resources, energy, personnel, <strong>and</strong> reactor time.<br />

Some <strong>of</strong> the attractive features <strong>of</strong> ACOMP include the fact that it provides an<br />

absolute characterization <strong>of</strong> the polymerization process <strong>and</strong> products in real time,<br />

<strong>and</strong> that it does not rely on chromatographic columns or flow injection devices.<br />

It requires that a very small stream <strong>of</strong> sample be continuously withdrawn from the<br />

reactor <strong>and</strong> diluted with a much larger quantity <strong>of</strong> solvent. This is because a highly<br />

dilute polymer solution is required in order to suppress strong intermolecular<br />

effects <strong>and</strong> arrive at the intrinsic properties <strong>of</strong> the polymer molecules themselves.<br />

© 2004 by Marcel Dekker, Inc.

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