Polystyrene

Phase diagrams for the system polystyrene-benzene-butanol were prepared by Bardet etal. (1969). The area of coacervation was defined and the different phases characterized in terms of their composition. The process of coacervation was related to the insolubilization of the polymer as a result of the strong interaction between the solvent and the non-solvent.

The coacervation of polystryene in a solution of cyclohexane by temperature lowering was investigated by Iso etal. (1985b). The polydispersity of the polymers was the important factor either to define the separation temperature for the separation of droplets or to determine the equilibrium composition of the dilute and coacervate phases. Microcapsules of glass beads had a thin film of the polymer and a thick coat of talc. The low efficiency of polymer utilization was improved by using a non-solvent for the polymer. Sodium sulfate crystals were encapsulated and the dissolution was related to the Higuchi model. It was found that the effective diffusion coefficient decreased as the encapsulation temperature was lowered.

In another paper, Iso etal. (1985a) investigated the three-component system polystyrene, cyclohexane and hexane and encapsulated glass beads and anhydrous sodium sulfate. The control of wall thickness was easier than when cyclohexane was used alone. The wall thickness was effectively controlled by adjusting the polymer concentration, the temperature of encapsulation and the amount of hexane added. The dissolution followed the Higuchi model.

Polystyrene was used to encapsulate frusemide or frusemide-PEG 6000 solid dispersion by El Shattawy etal. (1991). Coacervation was achieved by preparing a suspension of the drug in a solution of polystyrene in cyclohex-ane and effecting coacervation by adding the non-solvent petroleum ether. Dissolution studies in vitro, LD50 studies and oral toxicity of the polmyer were carried out in mice. The most suitable product was frusemide, PEG 6000, polystyrene with a weight ratio of 2:2:1. The dissolution of this product was slower than that of the pure drug and faster than that of the pure drug in polystyrene microcapsules. The toxicity studies showed good agreement between the increase in LDJ0 and the decrease in dissolution rate.

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