Calculating Polystyrene Mv Using GPC

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SUMMARY

This discussion focuses on calculating the weight-average molecular weight (Mv) of polystyrene using Gel Permeation Chromatography (GPC) data. The Mark–Houwink-Sakurada equation was employed, with parameters a = 0.678 and K = 0.00018 for the produced polystyrene, and a = 0.725 and K = 0.011 for the standard. Initial calculations yielded an Mv of 880.62, which was later corrected to 38419 after clarifying the lab manual's instructions. The confusion arose from the improper application of the equations and the need to compare literature values with GPC results.

PREREQUISITES
  • Understanding of Gel Permeation Chromatography (GPC)
  • Familiarity with the Mark–Houwink-Sakurada equation
  • Knowledge of intrinsic viscosity and its significance in polymer science
  • Basic skills in logarithmic calculations and molecular weight determination
NEXT STEPS
  • Review the Mark–Houwink-Sakurada equation for different polymers
  • Learn about GPC calibration methods and their impact on molecular weight calculations
  • Explore the significance of intrinsic viscosity in polymer characterization
  • Investigate common sources of error in GPC measurements and calculations
USEFUL FOR

Chemists, polymer scientists, and students involved in polymer characterization and analysis using GPC techniques will benefit from this discussion.

NotJohnson
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Homework Statement


I am trying to calculate Mv as part of a lab using GPC data for a polystyrene polymer that I produced with a known polystyrene standard. for the produced PS I have a = .678 and K = .00018 and the standard has a = .725 and K = .011. intrinsic viscosity was measured as .2346
Mn for the polymer from GPC is 23097 g/mol (for reference)
The solvent is THF, I'm not sure if the GPC is conventionally or universally calibrated

Homework Equations


IV (eta) = K*Mv^a (Mark–Houwink-Sakurada equation)

ln (Mv) (of PS produced) = 1/(asa + 1) * ln (Kst/Ksa) + (ast + 1) / (asa + 1) * ln (Mvst)
(sa = produced sample, st = standard) (equation correcting for GPC universal calibration)

The Attempt at a Solution


I used the Mark–Houwink-Sakurada equation and got Mv = 68.08 for the standard
I then used the below equation to solve for my sample and got Mv = 880.62

I am confused as to why this number is so much lower than the Mn or Mw. Is this normal or am I using the wrong procedure or equation to calculate this value?
 
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Never mind, apparently the lab manual worded this question very strangely. We were supposed to compare a and K from the literature to the ones from the GPC but only use the Mark–Houwink-Sakurada equation using the GPC values. Doing this gets an Mv of 38419 which is much more sensible (and ignore the effects of calibration method).
 

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