Intrinsic nonsolvent

POLYMERIZATION Solvent evacuation (SE) method and intrinsic nonsolvent (INS)... 

Akagi, K., Sakamaki, K., and Shirakawa, H., Intrinsic nonsolvent polymerization method for synthesis of polyacetylene films, Synth. Med., 55, 779-784 (1993). Catellani, M., Destri, S., and Bolognesi, A., New catalytic systems for acetylene polymerization, MakromoL Chem., 187, 1345-1349 (1986). 

Akagi, K. Sakamaki, K. Shirakawa, H. Intrinsic nonsolvent polymerization method for synthesis of highly stretchable and highly conductive polyacetylene films. Macromolecules 1992, 25, 6725-6726. 

The intrinsic nonsolvent (INS) polymerization protocol [34], where solvent is never employed, is a technique that is closely related to the solvent evacuation method. In a typical experiment, neat AlEt3 was dropped into neat Ti(OBu)4 in a Schlenk flask at 0°C. The catalyst was aged for 1 h at room temperature and then further aged for another hour at 150° C. The flask was degassed and rotated to coat its walls with the catalyst solution. The system was then cooled to —78°C and acetylene was added. The reaction was allowed to proceed for 30-60 min before quenching. The resulting PA film was washed with toluene at — 78°C and dried under vacuum. 

Based on these ideas, the intrinsic viscosity (in 0 concentration units) has been evaluated for ellipsoids of revolution. Figure 9.3 shows [77] versus a/b for oblate and prolate ellipsoids according to the Simha theory. Note that the intrinsic viscosity of serum albumin from Example 9.1-3.7(1.34) = 4.96 in volume fraction units-is also consistent with, say, a nonsolvated oblate ellipsoid of axial ratio about 5. 

The classical solvent precipitation fractionation technique provides reproducible fractionations for determining molecular weight distributions of CTPB and almost 100% recovery of the sample from the column. A solvent-nonsolvent combination which has been used effectively is the toluene—acetone-methanol system, where acetone and methanol are used as the nonsolvents. The precipitating fractions are required to stand approximately 24 hours to ensure complete separation. Each fraction is vacuum stripped of solvent at approximately 30 °C., and the molecular weight of each fraction is then determined by either VPO or intrinsic viscosity. 

Finally, we note that both solvation and ellipticity can occur together. The contours shown in Figure 4.13a illustrate how various combinations of solvation and ellipticity are compatible with an experimental intrinsic viscosity. The particle considered in Example 4.4 has an intrinsic viscosity of 4.50 and was calculated to be hydrated to the extent of 0.60 g HzO per gram of protein. The same value of [17] is also compatible with nonsolvated ellipsoids of... 

The only head-to-head polymer which has been examined for excimer fluorescence is polystyrene 25). Unfortunately, the synthetic route to this polymer leaves a number of stilbene-based structures in the sample, which have a lower-energy singlet state than either PS monomer (285 nm) or excimer (330 nm). Thus, fluorescence from these intrinsic stilbene traps was seen in the spectra of head-to-head PS in pure films and, to a lesser extent, in fluid solution. In the latter, the fluorescence of PS monomer was predominant, and the small amount of stilbene fluorescence was increased when a nonsolvent (methanol or cyclohexane) was added to the 2-methyl-tetrahydrofuran solution. In films of the polymer, stilbene fluorescence was the major spectral band, although some PS excimer fluorescence was also present in the spectrum. No monomer fluorescence at 285 nm was detected from films. Given the impure nature of the head-to-head PS sample, no conclusions on excimer formation in these systems could be drawn. 

The interesting phenomenon where a mixture of two poor solvents or nonsolvents for a polymer provides a medium that acts as a good solvent for die polymers has been the objective of many studies, by light scattering, " viscometry, " sorption equilibrium, and fluorescence. From these techniques, it has been possible to appreciate how the second virial coefficient Aj and the intrinsic viscosity [11] preferential adsorption coefficient A, and excimer and monomer emission ratio Ie/Im are involved by changing solvent composition. They present ([T)], A2) a maximum or a variation at a certain solvent composition where the polymer behaves as through it were dissolved in a good solvent. 

Carefully dried polyacids (e.g., by freeze-drying) dissolve extraordinarily well in water, even with high molar masses. After rigorous drying the solvation rate decreases. Other solvents for these polyacids are dioxane, dimethylformamide, and lower alcohols nonsolvents are acetone, ether, hydrocarbons, and the monomers. The solubility of poly(acrylic acid) increases with temperature, while the solubility of poly(methacrylic acid) decreases [445]. The solubility of the salts of the polyacids depends in a complex way on the pH value and the counterions. Alkali and ammonium salts are water soluble. Polyvalent cations form in water-swellable gels. The viscosity of aqueous solutions increases with the amount of polymer, to a constant value. Due to this experimental fact, it is not easy to calculate molar masses from the intrinsic viscosities [446]. 

A phenomenon called cosolvency, consisting in solution of a given polymer by two or mote nonsolvents in a mixture has also been observed with nylon 12, namely, in mixtures 2,2,3,3-tetrafluoropropanol/30—80 voL-% diloroform or 2,2,3,34etrafluoropropanol/45—60 voL—% toluene A feature characteristic of cosolvency is the dependence of intrinsic viscosity on the composition of the cosolvent mixture (Fig. 18), where the maximum of the curve corresponds to the compotition of the solvent with the relatively best thermodynamic quality. For such a solvent conqrotition none of its components is selectively sorbed by the polymer. ... 

Figure 43. Pure CO2/CH4 permeation ratios as a function of intrinsic viscosities of nonsolvent additives. Legend (1) 2-ethyl-1-hexanol (2) 1-octanol (3) 2-propanol (4) 2-decanol (5) 3,5,5-trimethyl-1-hexanol (6) 2,4-dimethyl-3-pentanol (7) 2,4,4-trimethyl-1-pentanol (10) 2-methyl-3-hexanol m merged d discrete...

The selectivity (permeance ratio) of the PPO membrane (asymmetric) tends to increase as the intrinsic viscosity of the polymer dissolved in the solvent/nonsolvent mixture increases. 

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