Handbook of Solvents - George Wypych - ChemTech - Ventech!

698 George Wypych
Figure 12.1.30. Molecular
model of polystyrene and
benzene rings alignment.
[Adapted by permission, from
J M Guenet, Macromol. Symp.,
114, 97 (1997).]
Carbonyl frequency shift, cm -1
1715
1710
1705
1700
1695
1690
Stress, MPa
20
15
10
1685
0 0.2 0.4 0.6 0.8 1
5
dichloromethane
no solvent
0
0 200 400 600
Strain, %
Figure 12.1.31. Stress-strain behavior at 130 o Cof
glassy sPS with and without immersion in
dichloromethane. [Data from C Daniel, L Guadagno,
V Vittoria, Macromol. Symp., 114, 217 (1997).]
cyclohexanone
N-methyl-2-pyrrolidone
Solvent molar fraction
Figure 12.1.32. Carbonyl frequency vs. molar
fraction of solvent. [Adapted, by permission, from
J M Gomez-Elvira, P Tiemblo, G Martinez, J Milan,
Macromol. Symp., 114, 151 (1997).]
whereas in chloroform
it takes
tens of hours.
Adding a small
amount of benzene
to the chloroformaccelerates
the gelation
process. There is
also evidence
from IR which
shows that the
orientation of the
ring plane is perpendicular
to the
chain axis. This
suggests that
there is a strong
interaction between
benzene
and sPS mole-
cules. The other interesting observation came
from studies on decalin sPS and iPS systems.
iPS forms a transparent gel and then becomes
turbid, gradually forming trigonal crystallites
of iPS. sPS does not convert to a gel but the
fine crystalline precipitate particles instead.
This shows that the molecular arrangement
depends on both the solvent type and on the
molecular structure of the polymer. 2
Figure 12.1.30 shows how benzene molecules
align themselves parallel to the phenyl
rings of polystyrene and how they are housed
within the helical form of the polymer structure
which is stabilized by the presence of solvent.
1
Work on poly(ethylene oxide) gels 7 indicates
that the presence of solvents such as
chloroform and carbon disulfide contributes to
the formation of a uniform helical conformation.
The gelation behavior and the gel struc-
ture depend on the solvent type which, in turn, is determined by solvent-polymer
interaction. In a good solvent, polythiophene molecules exist in coiled conformation. In a
poor solvent, the molecules form aggregates through the short substituents. 8
Polyvinylchloride, PVC, which has a low crystallinity, gives strong gels. Neutron diffraction
and scattering studies show that these strong gels result from the formation of