Preparation of Thermally Regenerable Ion-Exchange Resins by Polymerizing a Heterogeneous Mixture of Monomers

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Abstract
Crossinked resin beads containing regions of acidic and basic groups are the preferred structures for the efficient operation of a thermally regenerable ion-exchange process. In the present study they were prepared by polymerizing a heterogeneous mixture of acrylic esters and allylamines. Polymerization of unstable emulsions of acrylic esters and allylamines by heating the stirred emulsions gave very hard, strong resins which after hydrolysis had good acid, amine and thermally regenerable capacities. The thermally regenerable capacity depended very much on the nature of the acrylic ester and the allylamine. The order of increasing thermally regenerable capacity for the resins prepared is methyl acrylate (MA)/triallylamine (TAA), MA/diallylamine (DAA), MA/methyldiallylamine (MDAA) < ethyl acrylate (EA)/TAA, EA/DAA < EA/MDAA, butyl acrylate/MDAA. The dispersion of the unstable emulsions in a third phase resulted in immediate breakdown of the emulsion. The dispersion of partly prepolymerized emulsions in a third phase of paraffin oil containing talc, followed by completion of the polymerization and hydrolysis, gave hard resin beads with acid, amine and thermally regenerable capacities comparable to those prepared as a two-phase emulsion. Their shape, size, strength, and degree of agglomeration depended on the stirring rate, the shape and material of construction of the stirrer, the potential acid/base ratio of the monomers, the nature of the solid dispersant, and the acrylic ester and the allylamine. Satisfactory resin beads could be obtained from only the MA/TAA and MA/DAA combinations which are those that give resins with the poorest thermally regenerable capacities. Partial prepolymerization of the two-phase emulsion is easy on the laboratory scale, but would be impracticable on the commercial scale. Although polymeric dispersants gave stable two-phase emulsions, the amine monomer migrated into an aqueous third phase more rapidly than it polymerized.

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