Application Compendium - Agilent Technologies
Application Compendium - Agilent Technologies
Application Compendium - Agilent Technologies
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Figure 2 shows chromatograms of the standards in SEC and<br />
reversed-phase mode, and at the critical point where elution<br />
is independent of molecular weight.<br />
ACN/<br />
Water<br />
PEG 22,800 g/mol<br />
PEG 8,500 g/mol<br />
PEG 960 g/mol<br />
GPC/<br />
70% ACN<br />
Critical Point<br />
49% ACN<br />
Reversed-Phase<br />
40% ACN<br />
0.0 0.6 1.2 1.8 2.4<br />
3.0<br />
Figure 2. Analysis of PEG in SEC and reversed-phase to reveal the critical<br />
point.<br />
Figure 3 shows a chromatogram of the amine-modifi ed<br />
PEG material, before and after neutralization of the amine<br />
functionality with hydrochloric acid.<br />
0<br />
Diamine<br />
HCI<br />
PEG (8%)<br />
Mono amine<br />
Critical point<br />
for<br />
SEC mode -<br />
Mono amine (45%)<br />
PEG<br />
PEG-amine<br />
2 4 6 8<br />
min<br />
PEG-amine HCI salt<br />
Diamine (47%)<br />
Figure 3. Amine modifi ed PEG before and after neutralization with HCL.<br />
10<br />
3<br />
Before the addition of the acid, one peak was observed at<br />
total permeation (corresponding to unmodifi ed PEG) and<br />
two peaks were observed eluting in interactive mode (after<br />
total permeation of the column). The two peaks eluting in<br />
interactive mode were assigned as the mono and di-amine<br />
end-group modifi ed PEGs. Based on the peak areas, the ratio<br />
of components assigned as 8% PEG, 45% mono-amine and<br />
47% di-amine. Addition of the hydrochloric acid changed the<br />
elution to SEC mode (elution before the PEG peak), indicating<br />
the sensitivity of the chromatography at critical conditions to<br />
sample chemistry.<br />
LCCC Analysis of Poly(styrene-b-methyl methacrylate)<br />
Critical point chromatography was used to analyze a sample<br />
of poly(styrene-b-methyl methacrylate) block copolymer,<br />
whose structure is shown in Figure 4.<br />
C<br />
H 3<br />
Initiator fragment<br />
Styrene block<br />
Methyl methacrylate block<br />
H3C n<br />
O<br />
O<br />
Diphenyl ethylene linker<br />
H Terminating group<br />
n<br />
Figure 4. Structure of poly(styrene-b-methyl methacrylate).<br />
Critical conditions were established for both polystyrene and<br />
polymethyl methacrylate by running narrow standards of<br />
varying molecular weight using different isocratic mixtures of<br />
solvents.<br />
Figure 5 shows critical point diagrams for the polystyrene and<br />
polymethyl methacrylate standards.<br />
log Mp<br />
5<br />
4.6<br />
4.2<br />
3.8<br />
3.4<br />
1<br />
1.5 2 2.5 3<br />
min<br />
Figure 5a. Critical point diagrams for PS.<br />
100% THF 40% THF/ 40% THF/<br />
53% ACN<br />
60% ACN<br />
3.5