1. SIZE-EXCLUSION
CHROMATOGRAPHY OF
PERFLUOROSULFONATE
D IONOMERS
Nan Zhao
George Geevarghese

2. PART – I : INTRO
Nan Zhao

3.  INTRODUCTIO
N
 The authors want to measure the molar mass
distributions , Polymer conformation and
unperturbed dimensions of the
Polyfluorosulfonated ionomers which are
copolymers of tetrafluorethylene and sulfonic
acid-functionalized (SO3H) perfluorinated vinyl
ethers with SEC(with LS, DRI, DV)
SEC
LS
DRI, DV

4.  EXPERIMENTAL
 Testing Equipments:
SEC: Agilent 1100 seriesisocratic pump, autosampler and two-wavelength
spectrophotometric detector.
LS: Agilent PD2020 two-angle LS detector
DV: Malvern Model 270 DV detector
DRI: Waters Corporation Model 410 DRI detector
3 Columns: Agilent Olexis 7.5 mm×300 mm columns at 35.0 ◦C were used
with N,N-dimethylformamide (DMF) containing 0.1 M LiNO3.
 Materials: the authors used 3 classes of the Perfluorosulfonated
ionomers.
 The eluent was pre-filtered using 0.22 m Millipore GS filters.
 The flow rate was 1.0 mL/min
 0.2% acetone added to the samples as a flow marker
 The columns were calibrated with 15 PMMA narrow standards from
Agilent with molar masses between 580 and 1,400,000.

5.  EXPERIMENTAL
 Sample dissolution: He prepares a dilute ionomer
dispersion by using 80/20 n-propanol/water. The
dilute dispersion is then taken in the acid digestion
bomb.
 Then place the bomb in an oven heated from 30 to
230 ◦C at 5 ◦C per min, and then held for 6 h. After
that several hours were required to cool the vessels
down to room temperature.
 Then the autoclaved solutions were diluted 1:1 with
SEC sample solvent to give the SEC sample injection
concentration of ∼0.5 mg/mL.

6.  RESULTS AND DISCUSSION
 Five strategies the authors used
 SEC optimization
 Ionomer disolution
 increasing SEC detector signals
 (Calculation of molar mass distributions)
 (Polymer conformation and unperturbed dimensions)

7.  SEC OPTIMIZATION
 Because the sample has two solubility parameters which δ1=9.68
(cal/cm3)1/2 and δ2=16.71 (cal/cm3)1/2, the authors need to find a proper
solvent.
 Previously, Dr. Lousenberg and Hommura et al. used δ values of the
solvent closer to δ1 and closer to δ2 respectively.
 Due to some “unknows reason”, he choose the DMF(δ= 12.1),with as
the solvent.
 Then again, none of the perfluorosulfonatedionomers eluted from the
SEC columns using DMF(pure) he added 0.1M LiNO3 to improve the
elution.

8.  And because the non-autoclaved samples showed less linearity in the
log M calibration curve, he used autoclaved Nafion.
 SEC OPTIMIZATION

9. PART II –
4 STRATEGIES + CONCLUSION
George Geevarghese

10.  Ionomer dissolution
• Martin et al. - autoclave idea!
– 50/50 (v/v) n-propanol/water at 250 deg for 1hr (1wt%
incomer concentration)
– Author repeats (at 260 deg for 1hr & same conc., but fails
– But it worked (almost) at 230 deg for 6hrs & same conc., but
phase separated.
• Author finally used 0.1 M LiNO3 with DMF and added to 80/20
n-propanol/water
– That worked. BUT only for Nafion. C2 and C4 still showed
prepeaks.

11. • Then again, he realized at low wt % of ionomer (~0.2wt%)
prepeaks were less significant
• BUT, LS observed prepeaks at even small wt %. But, DRI
doesnt (even at higher conc)
• So he found an optimized conc @ 0.1wt%

12.  Increasing SEC detector signals
• The “optimized” “autoclaved” solution (0.1 wt%) was diluted 1:1
(w/w) with SEC samples
– But, results in large solvent peaks and detector signal
disruptions in the system peak region.
– This also reduced the injection concentrations of polymer ( to
0.5 mg/mL)
• DRI and LS are weak at this conc. because of small specific
refractive index increments (between −0.02 and −0.04
mL/g)
• Viscometry detector signals are weak because of the low
intrinsic viscosities

13. • So, he increased sample conc. by Solvent Exchange
 to ∼2 mg/mL
 SEC of this sample showed no aggregation(cos no prepeaks in
DRI)
• Can also improve DV signal by inc. the flow rate.
• Changing the solvent to NMP and DMSO will increase the specific
refractive index increment and improve DRI and LS detector signals
accordingly (complicated! high temp!)
1 g of SEC sample solvent is added to 3 g of 0.1 wt % 80/20 n-propanol/water
autoclaved solution. The mixed solvent is then partially evaporated with a nitrogen
stream to approximately 1.5 g. The lower boiling n-propanol and water are
preferentially removed while the sample concentration is increased.

14. Calculation of molar mass distributions

15. • Variation in dn/dc across the molecular size distribution caused by
comonomer compositional drift.
• Corrected by:
• Accounting for minor variation in dn/dc across the chromatogram (OR)
• Mark–Houwink calculation method

16.  Polymer conformation &
unperturbed dimensions
• Conformation plots of three ionomer classes are plotted. All
PFSA ionomers were observed to have lower viscosity at
equivalent molar mass than PMMA

17. • The unperturbed dimensions was calculated from SEC
viscosity–molar mass data
• It suggested suspicious free rotation of the perfluoroalkane
units (can be attributed to the unusual structure and behavior
of these materials)

18. Our Conclusions
• Advantages:
– SEC system with triple detection can
• give high accuracy for perfluorosulfonated ionomers.
• Most info can be obtained
– Solvent Exchange process can
• improve all detector signals
• Also reduce the water and n-propanol peaks observed
in the system peak region.
– The autoclaving procedure
• provides molecular solutions without re-aggregation
(better peaks)

19. Our Conclusions
• Disadvantages:
– Dissolution temp is high compared to other
techniques
– Solvent exchange is somewhat tedious and
requires careful weighing of solutions before and
after evaporation to obtain accurate injected
sample concentrations
– Even though small, Variation in dn/dc causes
error in molar mass and viscosity from its original
value

20. Reference
• Size-exclusion chromatography of perfluorosulfonated ionomers by T.H.
Moureya, L.A. Slater a, R.C. Galipoa, R.J. Koestnerb :
Journal of Chromatography A, 1218 (2011) 5801– 5809