Effect of percolation on free-radical polymerization of acrylamide in inverse microemulsion

Abstract

The kinetics of free-radical polymerization of acrylamide initiated by dibenzoyl peroxide in non-percolating and percolating inverse microemulsions (toluene/sodium bis(2-ethylhexyl) sulfosuccinate/water/acrylamide) and the properties of polyacrylamide particles formed from these inverse microemulsions were investigated. The acrylamide polymerization rate and polyacrylamide number-average molecular mass depend on the acrylamide concentration in the dispersed phase of the inverse microemulsion. For non-percolating inverse microemulsions these dependecies are described by the equation where x and y have the values of 1.8 and 1.4 respectively, while for percolating inverse microemulsions the respective values of x and y are 1.1 and 0.4. Data on polymer particle size and number-average molecular mass of polyacrylamide in polymer particles were used for calculation of the average number of polymer chains in polymer particles for non-percolating (approximately one chain per particle) and for percolating (more than two chains per particle) inverse microemulsions. The spin probe (potassium nitrosodisulfonate, Fremy's salt) correlation time τc expressing the spin probe mobility in water-swollen polymer particles and in polyacrylamide water solution pointed to the ‘collapsed’ state of polyacrylamide chains in polymer particles in both kinds of inverse microemulsions. Besides the dependencies of polyacrylamide polymerization rate and of number-average molecular mass of polyacrylamide on the acrylamide concentration in inverse microemulsions, the dependence of T50G values, characterizing the spin probe mobility in polymer particles of inverse microemulsions as a function of polyacrylamide concentration in the polymer particles, is different for nonpercolating and percolating inverse microemulsions.