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Viscosity Average Molecular weight using GPC data and Mark–Houwink-Sakurada equation

  1. Nov 16, 2009 #1
    1. The problem statement, all variables and given/known data
    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

    2. Relevant 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)

    3. 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?
     
    Last edited: Nov 16, 2009
  2. jcsd
  3. Nov 17, 2009 #2
    Re: Viscosity Average Molecular weight using GPC data and Mark–Houwink-Sakurada equat

    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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