molecular weight and polymer properties methods used to determine mn, mw membrane osmometry

Membrane Osmometry

Alfredo Clemente

CH 392NProf. Grant Willson.

The University of Texas Austin

Membrane Osmometry

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Molecular Weight and polymer propertiesMethods Used to determine Mn, MwMembrane Osmometry

Conclusions: Advantages and disadvantagesQuestions

Introduction and TheoryMeasuring Mn by osmotic pressure

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Molecular weight

Rel

ativ

e fra

ctio

n

Representative differential weight distribution curves1

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Relationship of polymer properties to molecular weight.1

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Typical Molecular Weight Determination Methods1

Method Type of mol. wt. avg. Range Info.

Light scattering (LS) To ∞ Shape

Membrane osmometry 2x104 to 2x106

Vapor phase osmometry To 4x104

Electron and X-ray microscopy 102 to ∞ Shape, dist

Ebulliometry To 4x104

Cryoscopy To 5x104

End Group Analysis To 2x104

Osmodialysis 500-2500Centrifugation To ∞SEC, with c detector Relative To ∞ Mol w Dist

SEC, with c and LS detectors To ∞ Mol w Dist

Viscometry Relative To ∞

nM

nMzwnM ,,

nMnMnMnMwzM ,

wnM ,

wM

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Membrane OsmometryIntroduction and Theory

Osmosis and Osmotic Pressure

Osmosis and Chemical Potential

h

011

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Equilibrium of Chemical Potential2

)(

)(

)(

)()..(

)(

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1011

10101

1,,1,,

1

,,

,,1,,

1

,,

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IVVnG

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IIIthenvolumesolutiontheeiVPGSince

PG

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IIthatfollowsitnGFrom

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nPTnnT

nnT

nnTnnT

nTPii

P

PnnT

j

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Osmotic Pressure

)(/21/

)(//

)(

)()(

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)(/21/

)(21/

221

22

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11

1

2

21

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11

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011

011

XIIIVnVxTVnT

XIIVnVx

XIVnV

Xnxn

xnnxn

IXVV

VIIIVTVxT

VIITxT

RR

RR

RR

for expression HugginsFloury

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Osmotic Pressure and

)(21RR

)(1)(/

)(21RR

)(

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221

2

21

12

2

1

1

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2

XXcVT

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XVIIVVx

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VT

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c

XVMc

mn

Vm

Vn

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nMn

M

n

nn

nn

n

i

iin

nM

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Osmotic Pressure and

)(...1R

)(R

)(R

232

0

XXIIIcAcAM

Tc

XXIIMT

c

XXIMT

c

n

nc

n

nM

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Osmotic Pressure and nM

Typical plot of osmometry experimental data

12

14

16

18

20

0 2 4 6 8 10 12

c/ g dm-3

(п/c

) / J

kg-

12

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Measuring by osmotic pressurenMMembrane osmometers used:

Static osmometer2

h•Equilibrium by natural diffusion

•Large cell volumes

•Long equilibrium times

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Measuring by osmotic pressurenMMembrane osmometers used:

Dynamic osometer3

•Equilibrium by reducing pressure on solution reservoir

•Small cell volumes

•Short equilibrium times

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Measuring by osmotic pressurenMMembrane osmometers used:

Dynamic osometer3

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Osmotic Pressure and nM 5

20.0°C:Slope = A2 = -2.0x10-4 cm3 mol/g2

1/intercept = Mn = 1.97x104 g/mol34.5°C:Slope = A2 = 1.7x10-5 cm3 mol/g2

1/intercept = Mn = 2.02x104 g/mol50.0°C:Slope = A2 = 1.7x10-5 cm3 mol/g2

1/intercept = Mn = 2.00x104 g/mol

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Conclusion: Advantages and disadvantages

DisadvantagesMembrane problems: leakage, asymmetry and ballooningOverestimation of molecular due low molecular weight moleculesNot suitable for electrolytes

AdvantagesAbsolute value of MnNo calibration with standards requiredIndependent of chemical heterogeneityApplicable to polymers with broad range of molecular weightsMeasurement of Mn within 10,000 to 2x106

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Questions?

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References1. Carraher, C. E., Jr Polymer Chemistry: An Introduction, 4th Ed., Marcel Dekker, NY: 1996.2. Young, R. J.; Lovell, P. A. Introduction to Polymers, 2nd Ed., Chapman & Hall, New York: 1991.3. Lipták B. G.; Brodgesell, A. Instrument Engineers' Handbook, Process measurement and analysis. CRC Press, Florida: 19954. W. R. Krigbaum and L. H. Sperling, J. Phys. Chem., 64, 99 (1960)5. Hiemenz, Paul C., Lodge, Timothy P.; Polymer Chemistry, 2nd Ed., CRC Press, Boca Raton: 2007.6. http://www.engga.uwo.ca/people/pcharpentier/392-2004/MW%20Measurement.pdf7. http://www.chem.ufl.edu/~polymer/instrumentation/vpo.html8. http://www.chem.ufl.edu/~polymer/instrumentation/vpo.html9. http://www.eng.uq.edu.au/files/course/files/CHEE2006/CHEE2006%20Week%2012_2.pdf

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References10. http://www.humancorp.co.kr/catalog/272-277.pdf11. http://www.gonotec.com/content.OSMO_090.PRODUCTS_CHEM.OSMO_090.USA.ENG.html12. http://www.princeton.edu/~pccm/facilities-polymersynth-eq.htm13 Chalmer, John M.; Meier, Robert J., Molecular Characterization and Analysis of polymers, Elsevier Science, Burlington: 2008