Chemistry Reference
In-Depth Information
100
1
101.5 bar
100
1
100
1
86.2 bar
100
1
100
1
74.1 bar
100
1
100
1
experimental MWD in
polymer-lean and polymer-rich phase
predicted MWD in
polymer-lean and polymer-rich phase
Fig. 18 Molecular weight distributions of polystyrene (mixture of two almost monodisperse
samples of 40 kg/mol and 160 kg/mol) in the coexisting phases of a polystyrene/cyclohexane/
carbon dioxide mixture at 170
C and varying pressures [
63
]. The two
left hand columns
give
the GPC analysis of the polymer lean and polymer rich phases. The
two right hand columns
show the molecular weight distributions as calculated using the SAFT model using 30 pseudo
components [
64
]
Polymers are often polydisperse with respect to molecular weight. Whereas this
is of minor importance for the solvent sorption in polymers (vapor liquid equilibrium),
this fact usually remarkably influences the polymer solubility (liquid liquid equilib-
rium). Therefore, polydispersity needs to be accounted for in interpretation and
modeling of experimental data. This can be done by applying continuous thermo-
dynamics as well as by choosing a representative set of pseudocomponents. It was
shown that a meaningful estimation of the phase boundary is possible when using
only two or three pseudocomponents as soon as they reflect the important moments
(
M
n
,
M
w
,
M
z
) of the molecular weight distribution.
