Chemistry Reference
In-Depth Information
a
6000
5000
4000
3000
2000
1000
0
02468 0 2 4 6 8 0 2
number of fraction
b
0,40
0,35
0,30
0,25
0,20
0,15
0
5
10
15
20
number of fraction
Fig. 18 Comparison of experimental [
75
](
symbols
) and calculated (
lines
) cross fractionations: (a)
fractionation with respect to the molecular weight, (b) fractionation with respect to the chemical
composition
experimental observation [
75
]. Although both one-direction fractionations lead to
very close results, they do not find the high molecular weight part of the distribution
of the original copolymer. Analyzing the fractionation according to the chemical
heterogeneity (Fig.
20b
), one can find that the cross-fractionation in comparison to
the one-direction fractionation improves the obtained integral distribution function
of the original copolymer; however, the complete distribution function could not be
recovered. From the thermodynamic point of view, the reason is the selection of the
corresponding solvent mixtures. The result could be improved by using a solvent
mixture having a larger difference in the parameter g
A
. Again, both one- direction
fractionations lead to similar results, but they are not able to reproduce the correct
original distribution according to the chemical heterogeneity. If the copolymer
