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254
Molecular weight averages are calculated directly according to the definitions,
using values for each slice:
M
n
=
c
i
i
=
1
n
∑
c
i
M
i
i
=
1
n
∑
M
w
=
c
i
M
i
i
=
1
n
∑
c
i
i
=
1
n
∑
The only assumption is that elution slices are monodisperse.
Molecular weight distributions
Molecular weight distributions are generated simply by plotting the relative
amount of polymer (amount or weight fraction per slice) as a function of the
molecular weight:
The figure above is a differential distribution. Another quite useful
representation of the same data is the cumulative distribution (cumulative
weight fraction as function of the molecular weight):
-0.01
0.00
0.01
0.02
0.03
0.04
0.05
1.0x10
4
1.0x10
5
1.0x10
6
1.0x10
7
Differential Weight Fraction
M olar M ass (g /mol)
D i fferential Molar Mass
1802__10
Norm = Log
1st order