Chemistry Reference
In-Depth Information
Table 5 Properties of poly(ethylene
co
acrylic acid) copolymer samples
Copolymer
M
n
(g/mol)
M
w
(g/mol)
M
w
/
M
n
Acrylic acid content (mol%)
Poly(E
96.2
co
AA
3.8
)
3.8
19,090
63,250
3.3
Poly(E
97.6
co
AA
2.4
)
2.4
22,713
258,214
11.4
Poly(E
96.9
co
AA
3.1
)
3.1
19,930
235,146
11.8
Poly(E
96.3
co
AA
3.7
)
3.7
23,443
227,427
9.7
Poly(E
95.4
co
AA
4.6
)
4.6
23,730
205,024
8.6
Table 6 Pseudocomponents for the copolymers poly(ethylene
co
acrylic acid)
Copolymer Pseudocomponents
j w
2
p,j
M
2
p,j
(g/mol)
Poly(E
96.2
co
AA
3.8
) 1 0.5 10,400
2 0.5 116,100
Poly(E
97.6
co
AA
2.4
) 1 0.673 15,433
2 0.327 757,509
Poly(E
96.9
co
AA
3.1
) 1 0.673 13,554
2 0.327 692,543
Poly(E
96.3
co
AA
3.7
) 1 0.669 158,74
2 0.331 655,259
Poly(E
95,4
co
AA
4,6
) 1 0.666 16,023
2 0.334 582,165
M
2
p,j
molecular weight of the pseudocomponent,
w
2
p,j
weight fraction of the pseudocomponent in
the solvent free system
Using the same pure-component and binary parameters, the phase boundary of
other poly(ethylene-
co
-acrylic acid) samples varying in copolymer composition,
molecular weight, and with even higher polydispersity can also be described
successfully, as demonstrated in Fig.
17
.
In some cases, e.g., for polymer fractionations, not only the phase boundary, but
also the molecular weight distribution in the coexisting phases is of interest.
In this case, it is useful to use the whole molecular weight distribution (see [
60
])
or a higher number of pseudocomponents for the modeling. As an example, Fig.
18
shows the molecular weight distributions of polystyrene in the two coexisting
phases observed with cyclohexane/carbon dioxide solvent mixture [
63
]. An initially
bimodal mixture of two polystyrene samples (40 kg/mol and 160 kg/mol) was
mixed with cyclohexane and carbon dioxide at 170
C and different pressures to
generate two liquid phases.
From the experimental data shown in Fig.
18
, it becomes obvious that the
shorter polymer species preferably dissolve in the polymer-lean phase whereas
the species of higher molecular weight accumulate in the polymer-rich phase. The
separation effect is best at low pressures where almost no longer polymers are
found in the polymer-lean phase. The selectivity decreases with increasing pres-
sures due to increasing solubility, also of the longer polymer species. Modeling
this system using about 30 pseudocomponents (right-hand side of Fig.
18
)leadsto
the same conclusion and shows an excellent agreement with the experimental
findings [
64
].
