The synthesis of ionomers with randomly distributed ionic blocks was achiev
ed by free radical copolymerization of a hydrophobic monomer with an ionic
comonomer in inverse microemulsions. The ionic monomer, sodium acrylate (ap
proximately 1 mol% based on the monomer feed) is encapsulated in the aqueou
s compartments of inverse micelles of sodium bis-(2-ethylhexyl)sulfosuccina
te. The hydrophobic monomer, methyl methacrylate or butyl acrylate, is diss
olved together with the initiator in the oil continuous phase (toluene). Fo
r 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 sal
t form and converted thereafter into Ca salts. Differential scanning calori
metry measurements performed on both series show a decrease in the glass-tr
ansition temperature for the Ca-poly(methyl methacrylate) ionomers upon inc
reasing N-H The results are discussed in terms of the nature of the counter
ion and of the ionomer microstructure.