ACRYLIC-ACID POLYMERIZATION KINETICS

The kinetics of the isothermal polymerization of acrylic acid were det ermined utilizing H-1-NMR spectroscopy. The polymerization rate was ob served to depend approximately on the 3/2 power of monomer and the 1/2 power of sodium persulfate concentration. This is consistent with a m odel in which the rate of initiation is itself dependent on the monome r concentration. The polymerization rate was also observed to have a s trong dependence on percent neutralization, decreasing with increasing level of neutralization up to 75 to 100% neutralization, and then inc reasing again. The activation energy for the rate of polymerization wa s between 9 and 13 kcal/mol except for 100% neutralized acrylic acid, which had an activation energy of 18 kcal/mol. These data suggest that a transition in mechanism occurred at 100% neutralization. Increasing the ionic strength by the addition of sodium chloride also increased the rate. The dependence of the molecular weight on the above variable s was also quantified for use in the model. It decreased with increasi ng conversion, decreasing ionic strength and increasing initiator. (C) 1997 John Wiley & Sons, Inc.