Application Compendium - Agilent Technologies

log Mp
5
4.6
4.2
3.8
0.5
15% Water / 15% ACN /
70% Water
17% Water / 17% ACN /
66% THF
1.5 2.5 3.5 4.5
min
Figure 5b. Critical point diagrams for PMMA.
19% Water / 17% ACN /
64% THF
Under the critical conditions for PMMA, chromatography of
PS resulted in elution based on adsorption mode.
Chromatograms of two polystyrene narrow standards eluting
under polymethyl methacrylate critical conditions are shown
in Figure 6.
0
Polystyrene Mp 580 g/mol
Polystyrene Mp 1260 g/mol
2 4 6 8
min
Figure 6. Chromatograms of polystyrene standards under polymethyl
methacrylate critical conditions.
Under the critical conditions for PS, PMMA resulted in elution
based on SEC.
Figure 7 shows chromatograms of a series of polymethyl
methacrylate narrow standards and a SEC calibration curve
obtained under the polystyrene critical conditions.
5.5
10
4
molecular weight
/ gmol -1
1.0E6
1.0E5
1.0E4
1.0E3
1.0
1.4 1.8 2.2 2.6
min
Figure 7. PMMA standards and SEC calibration curve run under PS critical
conditions.
The poly(styrene-b-methyl methacrylate) sample was
analyzed under the critical conditions for polystyrene.
Using these conditions, the elution is controlled purely by
the molecular weight of the methyl methacrylate block of
copolymer, the polystyrene block is ‘chromatographically
invisible’.
Figure 8 shows the molecular weight distributions of the
polystyrene block by conventional GPC using polystyrene
standards before introduction of the methyl methacrylate
and growth of the PMMA block, and the PMMA block under
critical conditions for polystyrene using PMMA standards.
dw/dlogM
6.0
4.8
3.6
2.4
1.2
0.0
3.5
PMMA block
by NMR = 30,300 g/mol
by SEC (PS LCCC)
= 29,400 g/mol
PMMA block
(SEC under PS LCCC,
PMMA standards)
3.9 4.3 4.7 5.1
min
PS block
(Normal SEC,
PS standards)
Figure 8. Molecular weight distributions of the styrene block before
reaction with PMMA, and the PMMA block under critical conditions for
polystyrene.
3.0
5.5