Synthesis of multiblock ionomers by copolymerization in inverse microemulsions

The synthesis of ionomers with randomly distributed ionic blocks was achieved by free radical copolymerization of a hydrophobic monomer with an ionic comonomer in inverse microemulsions. The ionic monomer, sodium acrylate (approximately 1 mol% based on the monomer feed) is encapsulated in the aqueous compartments of inverse micelles of sodium bis-(2-ethylhexyl)sulfosuccinate. The hydrophobic monomer, methyl methacrylate or butyl acrylate, is dissolved together with the initiator in the oil continuous phase (toluene). For a given hydrophobe/ionic monomer ratio, it is possible to tune the length of the ionic block in the ionomer by adjusting the initial number of ionic monomers per water droplet, N _H. The ionomers were obtained in their Na salt form and converted thereafter into Ca salts. Differential scanning calorimetry measurements performed on both series show a decrease in the glass-transition temperature for the Ca-poly(methyl methacrylate) ionomers upon increasing N _H. The results are discussed in terms of the nature of the counterion and of the ionomer microstructure. Received: 8 August 2000 Accepted: 24 October 2000