Handbook of Solvents - George Wypych - ChemTech - Ventech!

12.1 Rheological properties, aggregation, permeability 699
Figure 12.1.33. Crystal structure of poly(ethylene oxide) molecular complex with: (a) p-dichlorobenzene, (b) resorcinol,
(c) p-nitrophenol. [Adapted, by permission, from M Dosiere, Macromol. Symp., 114, 51 (1997).]
Figure 12.1.34. Optical micrograph
of PEO-resorcinol complex.
[Adapted, by permission, from
M Dosiere, Macromol. Symp., 114,
51 (1997).]
PVC-solvent complexes. 9 This indicates that the presence of
solvent may affect the mechanical properties of such a system.
Figure 12.1.31 shows that the presence of dichloromethane
in sPS changes the mechanical characteristic of the
material. A solvent-free polymer has a high elongation and
yield value. An oriented polymer containing dichloromethane
has lower elongation, no yield value, and approximately
four times greater tensile strength. 10
The interaction of polymer-solvent affects rheological
properties. Studies on a divinyl ether-maleic anhydride copolymer
show that molecular structure of the copolymer can
be altered by the solvent selected for synthesis. 11 Studies
have shown that the thermal and UV stability of PVC is affected
by the presence of solvents. 12-14
Figure 12.1.32 shows that solvent type and its molar
fraction affect the value of the carbonyl frequency shift. This
frequency shift occurs at a very low solvent concentration,
The slope angles for each solvent are noticeably different. 15 Similar frequency shifts were
reported for various solvents in polyetheretherketone, PEEK, solutions. 16
These associations are precursors of further ordering by crystallization. Figure 12.1.33
shows different crystalline structures of poly(ethylene oxide) with various solvents. 17 Depending
on the solvent type, a unit cell contains a variable number of monomers and molecules
of solvent stacked along the crystallographic axis. In the case of dichlorobenzene, the
molecular complex is orthorhombic with 10 monomers and 3 solvent molecules. Figure
12.1.34 shows optical micrograph of spherulite formed from unit cells having 8 monomers
and 4 molecules of solvent. The unit cell of the triclinic crystal, formed with nitrophenol, is
composed of 6 monomers and 4 molecules of solvent. This underlines the importance of
solvent selection in achieving the desired structure in the formed material. The technique is
also advantageous in polymer synthesis, in improving polymer stability, etc.