Solvents differentiating

Melt fracture of the extrudate was studied using M-45 wild photoautomat. Blend morphology was studied by SEM after differential solvent swelling. 

Ionic reactions of neutral substrates can show large solvent dependence, due to the differential solvent stabilization of the ionic intermediates and their associated dipolar transition states (Reichardt, 1988). This is the case for the electrophilic addition of bromine to alkenes (Ruasse, 1990, 1992 Ruasse et al., 1991) and the bromination of phenol (Tee and Bennett, 1988a), both of which have Grunwald-Winstein m values approximately equal to 1 so that the reactions are very much slower in media less polar than water. Such processes, therefore, would be expected to be retarded or even inhibited by CDs for two reasons (a) the formation of complexes with the CD lowers the free concentrations of the reactants and (b) slower reaction within the microenvironment of the less polar CD cavity (if it were sterically possible). 

Fig. 3.7 Normal-phase-HPLC chromatograms of PA fractions generated by differential solvent extraction of crude GSE (protocol 1). (a) Fraction 1, (b) Fraction 2, (c) Fraction 3, (d) Fraction 4, (e) Fraction 5, and (f) Fraction 6. Compounds were detected with post-column deiivatization using DMACA...

The ionization of the acid depends not only on the basicity of the solvent, but also on its dielectric constant and its ion-solvating ability. The dependence of the acidity and basicity constants of a compound on the basicity and acidity, respectively, of the solvents, leads to a distinction between leveling and differentiating solvents. When the solvent is a stronger base than water, its leveling effect will apply also to weaker acids. Similarly, strong bases will also have equal basicities in sufficiently acidic solvents. All bases stronger than the HO ion are adjusted to the basicity of this ion in water. 

Differentiating solvents are solvents in which neither the acidity of acids nor the basicity of bases is limited by the nature of the solvent. These solvents are not self-ionized. The aliphatic hydrocarbons and the halogenated hydrocarbons are such solvents. 

Table I lists the final results of solvent-swelling conditions which resulted in selecting 2,2,4-trimethylpentane and styrene at —25°C for a differential solvent pair. The table also includes the published values for the solubility parameters (a/CED) of the elastomers and the solvents. This table indicates that for the elastomer systems Cl-butyl-cts-polybutadiene or Cl-butyl-SBR excellent differentiation can be obtained.

Table I. Swelling of Various Elastomer Crosslinked Networks in Differential Solvents at — 25°C...

The system Cl-buty 1-natural rubber (or cw-polyisoprene) could not be resolved by differential solvent techniques because the polymeric solubility parameters were too similar. At one end of the spectrum—i.e., with styrene at — 25 °C—natural rubber could be highly swollen while restricting the chlorobutyl swell, but the reverse was not possible, as indicated by the swelling volumes in the trimethylpentane. As displayed in Table II, attempts to use a highly symmetrically branched hydrocarbon with a very low solubility parameter, served only to reduce both the swelling of natural rubber and chlorobutyl. (Neopentane is a gas above 10°C and a solid below — 20°C). Therefore, for this report the use of differential solvents in the study of interfacial bonding in blends was limited to systems of Cl-butyl and cw-polybutadiene or SBR. 

Figure 4. Blended systems of Figure 2 swollen in differential solvents at —25°C. Cure 30 minutes at 300°F.

Figure 5. Adhesion analysis of blends swollen in differential solvents...

Figure 10. Adhesion analysis after differential solvent swelling at —25°C...

ADHESION ANALYSIS AFTER DIFFERENTIAL SOLVENT SWELLING... 

Figure 12. Swelling in differential solvents at —25°C for the system SBR 1502, Cl-butyl tetramethylthiuram monosulfide formulation...

Figure 13. Swelling in differential solvents for the system Cl-butyl, SBR 1502 dipentamethylenethiuram tetrasulfide accelerator. Sulfur donor is DMTTS.

Figure 14. Blends of SBR and NBR swollen in differential solvent system acetone and cyclohexane...

Chebrolu, K.K. Jayaprakasha, G.K. Jifon, J. Patil, B.S. 2011. Optimization of flavanones extraction by modulating differential solvent densities and centrifuge temperatures. Talanta 85 353-362. 

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