Emulsifying Effect of Block and Graft Copolymers — Oil in Oil Emulsions

Summary

Block and graft copolymers act as oil in oil emulsifier for the corresponding incompatible homopolymers and for two non miscible liquids, each of them being a selective solvent of one of the sequences of the copolymer.

This emulsifying effect of polystyrene-polyisoprene block and graft copolymers has been studied for DMF-hexane mixtures, in function of the solvent volume ratio, the molecular weight, composition and structure of the copolymer.

Viscosity measurements on these oil in oil emulsions and determination of the particle size of the dispersed phase which have been performed, show that the type of emulsion, as well as the mean diameter of the dispersed phase is, a function of these parameters. It appears also that the continuous phase of the emulsion is preferentially formed by the solvent having the best solubility for the emulsifier.

Information on the emulsifying effect of block and graft copolymers may be of value for the design of polymeric composite systems, like ABS resins on High Impact Polystyrene.

It has been shown previously that block and graft copolymers act as oil in oil emulsifier for the corresponding incompatible homopolymers (1–4). Especially in polymeric composite systems, like ABS resins or High Impact Polystyrenes, it has been possible to show that block and graft copolymers regulate the particle size of the dispersed rubber phase and contribute to the adhesion at the boundery of the two phases (4–5).

In order to show that this emulsifying effect of A–B block and graft copolymers is a general behaviour, we have studied the simpler case of two non miscible liquids a and b, where we have not the inconvenience of high viscosity as for polymeric systems. The two non miscible liquids are choosen such that one of the liquids, say a, is a good solvent for the sequence A of the copolymer and a non solvent for the other sequence B. Reversely, the liquid b is a solvent of sequence B and a non-solvent for sequence A of the copolymer.

These requirements are met for the system acetonitrile-cyclohexane as immiscible solvents in presence of polystyrene-polymethylmethacrylate block or graft copolymers or also for the system DMF-n hexane in presence of polystyrene-polyisoprene (PS-PI) block or graft copolymers.

A preliminary report has already shown that these systems give stable oil-in-oil emulsions whereas random copolymers or mixtures of corresponding homopolymers have no emulsifying effect (6).

In order to complete these previous results, we have studied the system DMF-hexane-copolymers polystyrene-polyisoprene, in function of the molecular characteristics, e.g. molecular weight, composition and structure of the copolymer.