Investigation of the global phase behavior of polymer mixtures in the shield region.

This paper is a contribution of our systematic investigation of the global phase behaviors of the chain molecules mixtures, i.e., polymer mixture solutions. The phase behavior of fluid mixtures is understood by the critical lines in fluid-gas diagrams. The critical lines of binary fluid system may, under circumstances, exhibit closed loops in the critical lines. A distinction is made between free critical loops, as described by type VI in the Scott and van Konynenburg classification, and "rooted" critical loops, as found in the shield region. We define rooted loops as closed critical lines that are attached to the critical line structure by means of unstable critical line. We obtain the rooted loops in the global phase diagrams of the polymer mixture solutions within the framework of a model that combines the lattice gas model of Schouten, ten Seldam and Trappeniers with the Flory-Huggins theory, and we present the influence of the chain length of long molecules on the rooted critical loops. We present the results in the density-density and the temperature (T)-pressure (P) planes in detail.

Critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point using the combination of the Tompa model and the van der Waals equation.

We combine the modified Tompa model with the van der Waals equation to study critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point. The van Laar point is coined by Meijer and it is the only point at which the mathematical double point curve is stable. It is the intersection of the tricritical point and the double critical end point. We calculate the critical lines as a function of χ(1) and χ(2), the density of type I molecules and the density of type II molecules for various values of the system parameters; hence the global phase diagrams are presented and discussed in the density-density plane. We also investigate the connectivity of critical lines at the van Laar point and its vicinity and discuss these connections according to the Scott and van Konynenburg classifications. It is also found that the critical lines and phase behavior are extremely sensitive to small modifications in the system parameters.

Systematic investigation of global phase behavior of polymer mixtures in the pressure-temperature plane.

We investigate the critical lines of polymer mixtures in the presence of their vapor phase at the mathematical double point, where two critical lines meet and exchange branches, and its environment. The model used combines the lattice gas model of Schouten, ten Seldam and Trappeniers with the Flory-Huggins theory. The critical line structure is displayed for various combinations of the chain length and system parameters in the pressure (P)-temperature (T) plane, as is usually done with experimental results. This type of work sheds light on the essential transition mechanism involved in the phase diagram's change of character, such as multi-critical points and mathematical double points, which are of great practical importance in supercritical fluid extraction processes. The P, T diagrams are discussed in accordance with the Scott and van Konynenburg binary phase diagram classification. We found that our P, T plots were in agreement with type II, type III, or type IV phase diagram behaviors. We also found that some of our phase diagrams represent the liquid-liquid equilibria in polymer solutions and mixtures.

Global phase diagrams for a compressible polymer-solvent system using the full Tompa model.

We present the global phase diagrams for a compressible polymer-solvent system at the mathematical double point and its environment by using the full Tompa model for varying numbers of segments in each polymer chain. A principal transition mechanism is a mathematical double point at which two critical lines meet and exchange branches. We present the critical lines in the density-density and the P, T planes in detail. The locations of all significant features of the phase diagrams are described and compared with Scott and van Konynenburg phase diagram classifications. We find the type II, type III or type IV phase diagram behaviors of the Scott and van Konynenburg classifications. It is also found that the critical lines and phase behavior are extremely sensitive to small modifications in the chain length parameter.

3,4-Dimeth-oxy-N-(4-nitro-benzyl-idene)-aniline.

In the title mol-ecule, C(15)H(14)N(2)O(4), the dihedral angle between the two benzene rings is 29.52 (8)°. The nitro and two meth-oxy substituents are almost coplanar with their respective benzene rings. The crystal structure is stabilized by inter-molecular C-H⋯O inter-actions.

3,4-Dimeth-oxy-N-(3-nitro-benzyl-idene)aniline.

The title compound, C(15)H(14)N(2)O(4), has two crystallographically independent mol-ecules in the asymmetric unit. In both mol-ecules, the nitro and the two meth-oxy substituents are coplanar with the benzene rings to which they are attached. The benzene rings are nearly coplanar, with dihedral angles between the two benzene rings of 10.39 (8) and 5.95 (8)° in the two mol-ecules. The two independent mol-ecules in the asymmetric unit are rotated with respect to each other such that the dihedral angles between equivalent benzene rings are 49.11 (8) and 63.93 (8)°. In the crystal structure, inter-molecular C-H⋯O hydrogen-bond contacts and a weak C-H⋯π inter-action are observed.

4-(9-Anthr-yl)-1-(1-naphth-yl)spiro-[azetidine-3,9'-xanthen]-2-one n-hexane hemisolvate.

In the title compound, C(39)H(25)NO(2)·0.5C(6)H(14), the ß-lactam ring is nearly planar [maximum deviation of 0.012 (2) Šfrom the mean plane] and makes dihedral angles of 36.41 (13), 88.87 (13) and 54.16 (12)°, respectively, with the naphthalene, xanthene and anthracene ring systems. The mol-ecular conformation is stabilized by intra-molecular C-H⋯O and C-H⋯N contacts. The complete solvent mol-ecule is generated by inversion. In the crystal structure, mol-ecules are linked to each other by C-H⋯π inter-actions.

1,3-Bis(3-phenyl-prop-yl)-1H-benzimidazol-3-ium-2-carbodithio-ate.

The title compound, C(26)H(26)N(2)S(2), was synthesized from bis-[1,3-bis-(3-phenyl-prop-yl)benzimidazolidine-2-yl-idene] and CS(2) in toluene. The mol-ecular structure is composed of a benzimidazole ring system with two phenyl-propyl substituents and a dithio-carboxyl-ate group in the 2-position. The benzimidazole unit is essentially planar, with a maximum atomic deviation of 0.008 (2) Å, and makes dihedral angles of 72.72 (10) and 27.62 (12)°, with the two phenyl rings. The dihedral angle between the two phenyl rings is 55.98 (15)°. The mol-ecular packing is stabilized by a C-H⋯S inter-molecular hydrogen-bonding inter-action and a C-H⋯π inter-action between a benzene H atom and the phenyl ring of a neighbouring mol-ecule.