Phase Separation In Polymer Solutions Research Articles

Phase separation in polymer solutions. II. Determination of thermodynamic parameters of poly (2,6‐dimethyl‐1,4‐phenylene oxide) toluene mixtures

AbstractIn liquid systems where it is possible to perform light scattering experiments at the melting points of polymer solutions without nucleation taking place because of undercooling, the thermodynamic parameters necessary to calculate the correction parameter g in the Flory‐Huggins equation as modified by Koningsveld can be determined. In the system poly(2,6‐dimethyl 1,4‐phenylene oxide)‐toluene crystallization will be induced by liquid‐liquid phase separation at temperatures below the melting points. The Huggins interaction parameter x, calculated from light scattering data, shows negative values for solutions up to 24.5 weight per cent of polymer. This indicates specific interactions between polymer and solvent molecules. A combination of data from light scattering and from calculations based on the theory of melting point depression affords the values necessary for calculating the free enthalpy of mixing ΔG.

Structure formation in the systems polymer-solvent-precipitator in the region of their separation into layers

TI~E undoubted importance of investigations related to structure formation processes preceding phase separation in polymer solutions is due to the definite relationship between the nature of these processes and the resulting properties of the condensed phase. In liquid mixtures phase separation takes place as a result of a rise in the frequency and scale of fluctuations (which in the case of polymer-containing systems are often identified with macromolecular associates) accompanying a deterioration in the thermodynamic conditions underlying the existence of homogeneous solutions. The mechanism of formation of the new phase from the original homogeneous polymer solution largely depends on the nature of the latter and also on the quantitative and qualitative composition of the solution; in addition, the specific nature of macromolecules, compared with the molecules of simple liquids, suggests that structure formation processes involving the participation of macromolecules may take place long before intersection of the corresponding binodal surfaces. In this investigation an a t tempt was made to elucidate peculiarities of the behaviour of polymer solutions in mixed (two-component) solvents during the transition of the systems from the region of the homophase state on approaching the boundary of macro-separation into layers. Using dynamic birefringence and capillary viscometry techniques we investigated two extreme cases, taking as model high-molecular compounds polyisobutylene (PIB), with very high chain flexibility of the main valencies, and poly-7-benzyl-T,-glutamate (PBG) which in a-helix configuration corresponds to maximal chain rigidity.

Phase separation in polymer solutions. I. Liquid‐liquid phase separation of PPO poly (2, 6‐dimethyl 1, 4‐phenylene oxide) in binary mixtures with toluene and ternary mixtures with toluene and ethyl alcohol

AbstractIn the system poly(2, 6‐dimethy1‐1, 4‐phenylene oxide) (PPO)‐toluene three phase separation lines can be detected: the melting point curve, the cloud point curve, and the spinodial. Because crystallization of PPO occurs very slowly, a phase transition will always be initiated by liquid‐liquid phase separation. Depending upon the experimental circumstances two mechanisms are possible, either nucleation and growth (extremely slowly in this system) or the spinodial decomposition mechanism. In the system PPO‐toluene‐ethanol, liquid‐liquid phase separation occurs leading to two bulk liquid fractions. Only in mixtures containing very small concentrations of alcohol can three phase separation curves be detected from which the position of the cloud point curve of the system PPO‐toluene can be confirmed.

Liquid-liquid phase separation in concentrated solutions of non-crystallizable polymers by spinodal decomposition

Two mechanisms of liquid-liquid phase separation in polymer solutions are possible: nucleation and growth of one of the equilibrium phases, and decomposition by a spinodal mechanism. The conditions for and characteristics of both mechanisms are discussed. By combining a number of observations on phase separation in concentrated solutions of poly(2,6-dimethyl-1,4-phenylene ether) and of an ethylene — vinyl acetate copolymer in caprolactam, it becomes clear that a spinodal mechanism is operative at the onset of the separation process. In later stages the flow properties of the concentrated polymer phase determine the final state of the separated mixture.

Study of the treatment of polymer fractionation data

AbstractThe fractionations of a hypothetical 250‐component system and an actual polymer were simulated by computations on a digital computer. The results indicated that Schulz's method of treating polymer fractionation data is acceptable if the fractions obtained are reasonably sharp. When extremely low molecular weight materials are present in the polymer, the computation shows that one must be very careful in computing the M̄u/M̄n ratio. A comparison of the computation result with the experimental result of a linear polyethylene fractionation indicates that the Flory‐Huggins' theory describes the liquid‐liquid phase separation of polymer solutions well.

Phase separation in polymer solutions

Phase separation in polymer solutions

Phase separation in polymer solution

AbstractThe phase separation in solutions of high polymers in the same solvent (technically known as incompatibility) has been studied for fourteen high polymers (cellulose, vinyl, and acrylic derivatives) dissolved in thirteen solvents. The influence of solvent, concentration, molecular weight and constitution of the macromolecules has been studied for 78 mixtures: the results are represented in triangular diagrams. Incompatibility appears to be the normal situation, compatibility the exception. Moreover, in cetain cases the exception may be only apparent. Phase separation is discussed in its relation to osmotic pressure, solubility, and the isomorphism of the molecules. Phase separation furnishes new means—useful at leat for technical research—of measuring the molecular weight of macromolecules. It is a simple and rapid procedure.