Solvent/nonsolvent system

The coagulation process can now be considered in perspective of a ternary polymer-solvent-nonsolvent system, A schematic ternary phase diagram, at constant temperature, is shown in Figure 8. The boundaries of the isotropic and narrow biphasic (isotropic-nematic) regions are based on an extension of Flory s theory ( ) to a polymer-solvent-nonsolvent system, due to Russo and Miller (7). These boundaries are calculated for a polymer having an axial ratio of 100, and the following... 

Solvent/nonsolvent system. The solvent must be miscible with the nonsolvent (here an aqueous system). An aprotic polar solvent like N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl acetamide (DMAc) or dimethylsulfoxide (DMSO) is preferable for rapid precipitation (instantaneous demixing) upon immersion in the nonsolvent water. As a consequence, a high porosity anisotropic... 

Blnodal-splnodal phase diagram, polymer-solvent-nonsolvent system, 230-32... 

The physicochemical properties of alkylated polysaccharides have received some attention, and details of the structures and conformations of 0-methylcelluloses, and their interaction in micelle junctions, have been included in a thorough discussion of polysaccharide gels and networks. Information on the polydispersity of samples of partially methylated cellulose may be obtained from column fractionation and by fractional precipitation from a solvent-nonsolvent system, but, for a more complete characterization of polydispersity, fractionation with a series of solvent-nonsolvent systems is necessary. The solubility, in water, of polysaccharides that are mainly methylated may be considerably improved by introduction of a few suitable ionizing groups, for example, by reaction with monochloroacetic acid to introduce carboxymethyl ether groups. The general sorption and diflFusion features of hydrocarbons and other... 

Another coil-rod-coil triblock copolymer 25 with PS as the flexible block and PPE as the rigid segment has been synthesized by Li and Wang. The aggregation behavior of this copolymer was investigated in selective solvents and in solvent/nonsolvent systems. It was clearly demonstrated that the solvent composition greatly affected the polymer s conformation and the aggregate formation. 

One of the main variables in the immersion precipitation process is the choice of the solvent/nonsolvent system. In order to prepare a membrane from a polymer by phase inversion the polymer must be soluble. Although one or more solvents may be suitable for the chosen polymer, the solvent and nonsolvent must be completely miscible. Water is frequently used as a nonsolvent but other nonsolvents can also be used. Some solvents for cellulose acetate and polysulfone which are miscible with water are listed in table III.6. The solubility of these organic solvents with water must be considered further. As described in the previous section, the miscibility of components of all kind is determined by the free enthalpy of mixing... 

GA Ogawa, T. and Hoshino, S., Cloud points in isotactic polypropylene-solvent-nonsolvent systems (Jap.), Kobunshi Kagaku, 28, 348, 1971. 

WAN Wang, D., Li, K., and Teo, W.K., Phase separation in polyetherimide/solvent/ nonsolvent systems and membrane formation, J. Appl. Polym. Sci., 71, 1789, 1999. 

SAX Saxena, R. and Caneba, G.T., Studies of spinodal decomposition in a ternary polymer-solvent-nonsolvent system, Polym. Eng. Sci., 42, 1019, 2002. 

A. Filimon, E. Avram, and S. loan, Structure-rheology relationship in complex quaternized polysulfones/solvent/nonsolvent systems. Polym. Bull. 70,1835-1851 (2013). 

MOR Morimoto, S. and Ohtani, N., Phase separation enthalpies of polymer solids in ternary polymer-solvent-nonsolvent systems (Jap.), Kenkyu Hokoku Seni Kobunshi Zairyo Kenkyushu, 119, 35, 1979. 

To obtain quantitative representation of fractionation, a model for the thermodynamic properties of the copolymer + solvent + nonsolvent system and the original two-dimensional distribution function are required. Ratzsch et al. [46] presented the application of continuous thermodynamics to successive homopolymer fractionation procedures based on solubility differences. This method is now applied to copolymer fractionation. The liquid-liquid equilibria (LLE) of polymer solutions forms the thermodynamic background for these procedures. The introduction of the precipitation rate (23) permits calculation of the distribution functions in the sol and gel phases of every fractionation step, i, according to ... 

Setting a = in (16) means that the distribution functiOTi with respect to the chemical heterogeneity is symmetrical. The parameters describing the selected solvent + nonsolvent system occur in the G model [i.e., (5)]. For the model calculation, the following parameter were chosen ... 

The sample is first fractionated into intermediate fractions in one solvent + nonsolvent system (solvent mixtnre 1). This is followed by further fractionation of these intermediate fractions by another solvent + nonsolvent system (solvent mixture 2). 

Figure 7.6 illustrates a ternary phase diagram for a polymer-polymer-common solvent system. Sketch a ternary phase diagram for a polymer-solvent-nonsolvent system. Include tie lines and illustrate the effects of temperature and polymer molecular weight. Assume that the solvent and nonsolvent are soluble in all proportions. 

The tables contain qualitative solubility data for a selected number of polymers. Since no standard definition for solvent-nonsolvent systems has been used in most of the original sources, the recognition of a certain compound as a solvent or nonsolvent is to some extent influenced by personal interpretation. No attempt has been made to edit the original information. Division into only two classes, solvents and nonsolvents, is dictated by the practical point of view. For more quantitative information, the user is referred to the tables of theta solvents and fractionation of polymers in this Handbook. 

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