Molecular Weight and polymer properties

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• Molecular Weight and polymer properties
• Methods Used to determine Mn, Mw
• Membrane Osmometry
• Conclusions Advantages and disadvantages
• Questions

• Introduction and Theory
• Measuring Mn by osmotic pressure

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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 8 Shape
Membrane osmometry 2x104 to 2x106
Vapor phase osmometry To 4x104
Electron and X-ray microscopy 102 to 8 Shape, dist
Ebulliometry To 4x104
Cryoscopy To 5x104
End Group Analysis To 2x104
Osmodialysis 500-2500
Centrifugation To 8
SEC, with c detector Relative To 8 Mol w Dist
SEC, with c and LS detectors To 8 Mol w Dist
Viscometry Relative To 8
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• Membrane Osmometry
• Introduction and Theory

Osmosis and Osmotic Pressure Osmosis and
Chemical Potential
h
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• Equilibrium of Chemical Potential2

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• Osmotic Pressure

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• Osmotic Pressure and

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• Osmotic Pressure and

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• Osmotic Pressure and

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• Measuring by osmotic pressure

Membrane osmometers used

• Static osmometer2

• Equilibrium by natural diffusion
• Large cell volumes
• Long equilibrium times

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• Measuring by osmotic pressure

Membrane osmometers used

• Dynamic osometer3

• Equilibrium by reducing pressure on solution
  reservoir
• Small cell volumes
• Short equilibrium times

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• Measuring by osmotic pressure

Membrane osmometers used

• Dynamic osometer3

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• Osmotic Pressure and

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20.0CSlope A2 -2.0x10-4 cm3
mol/g2 1/intercept Mn 1.97x104
g/mol 34.5CSlope A2 1.7x10-5 cm3
mol/g2 1/intercept Mn 2.02x104
g/mol 50.0CSlope A2 1.7x10-5 cm3
mol/g2 1/intercept Mn 2.00x104 g/mol
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• Conclusion Advantages and disadvantages

• Disadvantages
• Membrane problems leakage, asymmetry and
  ballooning
• Overestimation of molecular due low molecular
  weight molecules
• Not suitable for electrolytes

• Advantages
• Absolute value of Mn
• No calibration with standards required
• Independent of chemical heterogeneity
• Applicable to polymers with broad range of
  molecular weights
• Measurement of Mn within 10,000 to 2x106

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• Questions?

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• References

1. 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 1995 4. 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/pch
arpentier/392-2004/MW20Measurement.pdf 7.
http//www.chem.ufl.edu/polymer/instrumentation/v
po.html 8. http//www.chem.ufl.edu/polymer/instru
mentation/vpo.html 9. http//www.eng.uq.edu.au/fil
es/course/files/CHEE2006/CHEE200620Week2012_2.pd
f
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• References

10. http//www.humancorp.co.kr/catalog/272-277.pdf
11. http//www.gonotec.com/content.OSMO_090.PRODU
CTS_CHEM.OSMO_090.USA.ENG.html 12.
http//www.princeton.edu/pccm/facilities-polymers
ynth-eq.htm 13 Chalmer, John M. Meier, Robert
J., Molecular Characterization and Analysis of
polymers, Elsevier Science, Burlington 2008
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