Chemistry Reference
In-Depth Information
Fig. 17 Solubilities of poly(ethylene
co
acrylic acid) copolymers with different acrylic acid
contents in ethene. The polymer concentration is 5 wt%. The properties of the copolymers are
given in Table
5
.
Lines
show predictions using PC SAFT and the pseudocomponents given in
Table
6
[
43
].
Symbols
represent experimental data [
62
]:
Circles
poly(E
95.4
co
AA
4.6
),
squares
poly(E
96.3
co
AA
3.7
),
triangles
poly(E
96.9
co
AA
3.1
),
diamonds
poly(E
97.6
co
AA
2.4
)
7 Summary
State-of-the-art equations of state like SAFT and PC-SAFT are based on a sound
physical background and are able to explicitly account for various molecular
properties such as the nonspherical shape, the ability to form hydrogen bonds or
the polarity. These models usually require three (for nonassociating molecules) or
five pure-component parameters (for associating molecules) that have a physical
meaning. Whereas for solvents these parameters are usually determined from fitting
to vapor pressures and liquid densities, a different approach is applied to polymers.
Because vapor pressures are not accessible for these molecules, polymer parameters
are fitted to the experimental data of a polymer/solvent binary system. It could be
shown that although fitted to binary data, these parameters have a physical meaning
and do characterize the considered polymer molecule. Using these parameters, the
phase equilibrium of homopolymer systems can be described as a function of
temperature, pressure, polymer concentration, molecular weight, and even the
polymer molecular weight distribution.
The extension to copolymer systems is straightforward. The parameters for the
different polymer units as well as the binary parameters for their interaction with
the solvent can be used as determined for the respective homopolymer systems.
Using only one additional binary parameter that describes the interactions of the
unlike monomer units in the copolymer system, the phase behavior of copolymer
systems can be described and even predicted over a wide range of copolymer
compositions.
