Swelling by solvents

SAN resins show considerable resistance to solvents and are insoluble in carbon tetrachloride, ethyl alcohol, gasoline, and hydrocarbon solvents. They are swelled by solvents such as ben2ene, ether, and toluene. Polar solvents such as acetone, chloroform, dioxane, methyl ethyl ketone, and pyridine will dissolve SAN (14). The interactions of various solvents and SAN copolymers containing up to 52% acrylonitrile have been studied along with their thermodynamic parameters, ie, the second virial coefficient, free-energy parameter, expansion factor, and intrinsic viscosity (15). 

High-density polyethylene (p = 0.94-0.96 g/cm ) has up to five times the stiffness of low-density polyethylene at ambient temperatures and can be used at much higher temperatures. Its chemical resistance is similar to that of the low-density grades, but the resistance to swelling by solvents is higher. 

We have omitted a great deal of detail in this discussion of polymer viscosity. The interested reader will find some of the missing information supplied in Flory (1953). In particular, we have omitted all numerical coefficients, which limits us to ratios as far as computational capability is concerned. Numerical coefficients are available for Equation (92), for example, and this allows coil dimensions to be evaluated from viscosity measurements. A general conclusion that unifies all of this section is that any factor that causes a polymer chain to be more extended in space —whether by coil unfolding or swelling by solvent —tends to increase [77]. This is exactly what we expect in terms of the purely qualitative picture provided by Figure 4.8. Example 4.6 illustrates this for some actual polymers. 

Crosslinking in polyurethanes leads to a decrease in the molecular mobility and flexibility and causes an increase of rigidity, softening points and modulus of elasticity and reduces elongation and swelling by solvents (only linear polymers are soluble, crosslinked polymers are only swelled by the organic solvents). 

Following the speculations raised by the above results, it was considered important to devise experiments which would make it possible to observe stress softening in vulcanizates as a result of swelling by solvents. This phenomenon had not been observed before. The experimental scheme was based on the observation that stress softening apparently recovers faster the higher is its temperature (see Fig. 5) and that presumably, at temperatures approaching Tg no recovery should take place. Rigbi75) showed that at 0 °C, recovery is extremely slow even in compounds for which Tg is of the order of -40°. However, when the rubber is swollen in a solvent,... 

Many attempts have been made to produce synthetic rubber-like polymers. One such polymer, Thiokol, which is very resistant to abrasion and to swelling by solvents, results from condensation polymerization of ethylene dichloride and sodium polysulfide. 

Fluoropolymers n. Polymers whose repeating units contain fluorine. Such polymers often have outstanding thermal, thermo-oxidative, and chemical resistance, both to chemical attack and to swelling by solvents. Flushed color n. A color base in paste form prepared by flushing. 

By using an optical microscope, solvent condensation could be followed in real time and direct space via the change of the interference colors of the film. As the amount of polymer in the film stayed constant (this quantity is proportional to the thickness of the dry spin-coated film), a change in film thickness was directly related to the amount of solvent incorporated into the film, i.e., corresponded to swelling by solvent. From the interference colors the thickness h) of the swollen film could be deduced. The initial film thickness ho) was determined by ellipsometry. Accordingly, the polymer concentration cp in the solution of the swollen film was determined by ... 

A number of studies on different ICPs have shown similar data to that given in Figure 10.11, with a decreasing actuation occurring when higher isotonic stresses are applied [19, 24, 57]. These observations reflect the fact that, in most cases, the modulus is smaller in the contracted state. The modulus of solvent swollen network polymers is known to be influenced by two factors. Firstly, the swelling by solvent reduces the concentration of load-bearing chains, so that the modulus tends to decrease. Secondly, as... 

Similar techniques can be used to study softening and penetration, swelling by solvent and sintering. 

Low solvent resistance - Most plastics are swelled by solvents some are weakened by boiling water. 

From Table 13 it is obvious that the solvent treatment decreased both PWP and MWCO due to membrane swelling by solvent. The change in MWCO was more than the change in PWP. 

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