28.02.2013 Views

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Figure 9 HOPCretentioncurveinseparation<strong>of</strong>PCL10KbyaTMS-120Bcolumn(open<br />

circles), a TMS-75B column (closed squares), <strong>and</strong> a C8-75B column (crosses).<br />

pore size with TMS surface, the peak concentration did not reach the level <strong>of</strong> the<br />

injected solution.WiththeC8-75B,theinjectionwasless,probablybecause <strong>of</strong>an<br />

even smaller pore size due to surface modification <strong>and</strong> some repulsion from the<br />

octyl moieties. The peak concentration was considerably lower. Recovery was<br />

below100%(85,86,<strong>and</strong>85%,respectively,inthethreeseparations),butwashing<br />

the column in dioxane at 808C released all the polymer adsorbed.<br />

Thethreeparts<strong>of</strong>Fig.10showSECchromatograms.Fractions1to16were<br />

eluted in toluene at 308C. Later fractions were collected at ahigher temperature<br />

either in toluene or dioxane. These last fractions reveal which components <strong>of</strong><br />

PCL10K were adsorbed onto the pore surface. The overall tendency is similar<br />

among the three columns, but distinctly different from the one obtained with<br />

nonadsorbing environment (C8-120B). The increase in the peak retention time<br />

with an increasing fraction number is more gradual compared with Fig. 8,<br />

especiallyinFig.10c.Middlefractionsmaintainanarrowerdistributioncompared<br />

with that <strong>of</strong> the original PCL10K. Late fractions are enriched with low-MW<br />

components,especiallyintheseparationbyTMSsurfaces.Themultimodalnature<br />

<strong>of</strong> the MW distribution is revealed. Unlike the column C8-120B, the C8-75B<br />

columnadsorbedPCL10K.Itwasconsideredthatalowerdegree<strong>of</strong>substitution<strong>of</strong><br />

surface silanols with octyl moieties in C8-75B than in C8-120B resulted in<br />

adsorption (9). Separation <strong>of</strong> the same polymer by octadecyl (C18)-modified<br />

CPG75B was attempted, but there was little adsorption, <strong>and</strong> the fractions had a<br />

broader MW distribution compared with the weakly adsorbing surfaces.<br />

Table 2lists the mass <strong>of</strong> polymer <strong>and</strong> its average MW for some <strong>of</strong> the<br />

fractions obtained in the separation with the C8-75B column. Now the mass <strong>of</strong><br />

polymer with Mw=Mn ,1:2 is 88.6mg as opposed to amere 6.2mg in the<br />

separation with the C8-120B column in toluene.<br />

© 2004 by Marcel Dekker, Inc.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!