Chemistry Reference
In-Depth Information
a
b
MMA
MMA
0.0
1.0
0.0
1.0
0.2
0.8
0.2
0.8
0.4
0.6
0.4
0.6
0.6
0.4
0.6
0.4
0.8
0.2
0.8
0.2
1.0
0.0
1.0
0.0
PMMA
PMMA
CO
2
CO
2
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Fig. 10 Phase behavior of the system PMMA (
M
w
= 18 kg/mol)/MMA/CO
2
at 65
C[
45
].
Squares
and
circles
represent experimental cloud point data. The
solid lines
(phase boundary) and
dashed
lines
(tie lines) are calculated with PC SAFT.
Triangles
represent the VLLE region. (a)
p
= 100
bar, (b)
p
= 150 bar
of 100 bar this system exhibits a three-phase region that can be suppressed by
increasing the system pressure up to 160 bar. Moreover, this behavior strongly
depends on temperature and the molecular weight of the polymer. Using only pure-
component and binary parameters for the three subsystems the phase behavior and
even the presence or absence of the three-phase region can be described by PC-
SAFT in excellent agreement with the experimental data.
5 Extension to Copolymers
The original versions of the above-mentioned perturbation theories (e.g., SAFT or
PC-SAFT) consider a molecule as a chain of identical segments. Extensions of
these models allow for taking into account different types of segments and can
therefore describe copolymer systems [
50 52
]. The extension of PC-SAFT to
copolymers is referred to as copolymer PC-SAFT [
53
].
Now, the monomer segments are allowed to differ in size as well as in attractive
or electrostatic interactions (such as dispersion energy, association, polarity)
(Fig.
11
). Thus, each of the different monomer units is described by its own
parameter set (for nonassociating and nonpolar monomers:
m
,
s
,
e
).
The relative amount of monomer units is usually given by the experimental
polymer characterization. The relative amount of segments
a
and
b
is described by
segment fractions
z
a
and
z
b
(
z
a
þ
z
b
¼
1) within the copolymer, which are defined
as:
m
m
ð
z
a
¼
analogously for
bÞ
(22)
