Polystyrene/solvent phase equilibria

Tong, Z. Einaga, Y. Fujita, H., "Phase Equilibrium in Polymer + Polymer + Solvent Ternary Systems. III. Polystyrene + Polyisoprene + Cyclohexane System Revisited," Polym. J., 19, 965 (1987). 

Graft Copolymers. In graft copolymerization, a preformed polymer with residual double bonds or active hydrogens is either dispersed or dissolved in the monomer in the absence or presence of a solvent. On this backbone, the monomer is grafted in free-radical reaction. Impact polystyrene is made commercially in three steps first, solid polybutadiene rubber is cut and dispersed as small particles in styrene monomer. Secondly, bulk prepolymerization and thirdly, completion of the polymerization in either bulk or aqueous suspension is made. During the prepolymerization step, styrene starts to polymerize by itself forming droplets of polystyrene with phase separation. When equal phase volumes are attained, phase inversion occurs. The droplets of polystyrene become the continuous phase in which the rubber particles are dispersed. R. L. Kruse has determined the solubility parameter for the phase equilibrium. 

In the late 1970s when they looked over the existing literature, Hashizume et al. noticed that even for the simplest of quasi-binary solutions, i.e., ternary solutions containing two homologous polymers in a single solvent, systematic phase equilibrium data were virtually lacking. Since such data seemed essential for testing any proposed expression for g for quasi-binary solutions, they [22] undertook extensive measurements of cloud-point curves, binodals, and critical points on mixtures of two narrow-distribution polystyrenes f4 and flO dissolved... 

T01 Tong, Z., Einaga, Y., Miyashita, H., and Fujita, H., Phase equilibrium in polymer + polymer + solvent ternary systems. 2. Phase diagram of polystyrene + polyisoprene + cyclohexane, Macroffro/ecw/ex, 20, 1888, 1987. 

If two different polymers can be dissolved successfully in a common solvent, a molecular intermixing of the dissolved macromolecules should occur due to the fast establishment of the thermodynamic equilibrium. The difficulty with this procedure is due to the fact that very many polymers become incompatible above a certain concentration when their solutions in a common solvent are combined. This means that the originally homogeneous solutions of polymers A and B separate into two phases when being combined, whereby each of the phases contain different quantitative proportions A B [e.g., polystyrene and poly(vinyl acetate) in toluene]. But even when two polymers have been dissolved sue-... 

For ternary polymer-polymer-solvent systems, the compositions of the equilibrium phases may be determined using a variety of microanalytical methods depending upon the chemical nature of the polymers (Dobry and Boyer-Kawenoki, 1947). Each of the phases is sampled, weighed, and dried to determine the solvent concentration. If the two polymers are sufficiently different chemically, microanalytical determination of carbon and hydrogen may be used. In systems containing polystyrene, the proportion of polystyrene may be determined by precipitating it with acetic acid and weighing the precipitate. Other microanalytical methods have also been used to determine phase compositions. 

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