Handbook of Solvents - George Wypych - ChemTech - Ventech!

700 George Wypych
Temperature is an essential parameter in the crystallization process. 18 Rapid cooling of
a polycarbonate, PC, solution in benzene resulted in extremely high crystallinity (46.4%) as
compared to the typical PC crystallinity of about 30%.
Polymer-solvent interaction combined with the application of an external force leads
to the surface crazing of materials. The process is based on similar principles as discussed in
this section formation of fibrilar crystalline structures.
Although research on molecular structure and crystallization is yet to formulate a theoretical
background which might predict the effect of different solvents on the fine structure
of different polymers, studies have uncovered numerous issues which cause concern but
which also point to new applications. A major concern is the effect of solvents on craze formation,
and on thermal and UV degradation. Potential applications include engineering of
polymer morphology by synthesis in the presence of selected solvent under a controlled
thermal regime, polymer reinforcement by interaction with smaller molecules, better retention
of additives, and modification of surface properties to change adhesion or to improve
surface uniformity, etc.
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12.1.5 OTHER PROPERTIES AFFECTED BY SOLVENTS
Many other properties of solutes and solutions are affected by solvents. Here, we will
discuss material stability and stabilization, some aspects of reactivity (more information on
this subject appears in Chapter 13), physical properties, some aspects of electrical and
electrochemical properties (more information on this subject appears in Chapter 11),
surface properties, and polarity and donor properties of solvents.
Degradative processes have long been known to be promoted by the products of solvent
degradation. Tetrahydrofuran is oxidized to form a peroxide which then dissociates to
form two radicals initiating a chain of photo-oxidation reactions. Figure 12.1.35 shows the
kinetics of hydroperoxide formation. 1 Similar observations, but in polymer system, were
made in xylene by direct determination of the radicals formed using ESR. 2 An increased
concentration in trace quantities of xylene contributed to the formation of n-octane radicals