Molar Mass Distribution - Definition of Molar Mass Averages

Definition of Molar Mass Averages

Different average values can be defined depending on the statistical method that is applied. The weighted mean can be taken with the weight fraction, the mole fraction or the volume fraction:

  • Number average molar mass or Mn
  • Weight average molar mass or Mw
  • Viscosity average molar mass or Mv
  • Z average molar mass or Mz

M_n=\frac{\sum M_i N_i} {\sum N_i}, M_w=\frac{\sum M_i^2 N_i} {\sum M_i N_i}, M_z=\frac{\sum M_i^3 N_i} {\sum M_i^2 N_i}, M_v=\left^\frac{1} {a}

Here a is the exponent in the Mark-Houwink equation that relates the intrinsic viscosity to molar mass.

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