Precipitation polymerization of acrylic acid in toluene. I: synthesis, characterization and kinetics

Abstract

Acrylic acid was isothermally polymerized by precipitation polymerization in toluene at various monomer and initiator concentrations over the temperature range of 40°C–50°C. 2,2′-azobis (2,4-dimethyl-valeronitrile) was employed as a chemical initiator. The rate of polymerization was found to depend on the monomer and initiator concentration to the 1.7th and 0.6th orders, respectively. The greater than first order dependence on monomer concentration signifies a secondary, monomer-enhanced, decomposition step for the initiator molecules. The approximately 0.5 order dependence of the rate of precipitation polymerization on the initiator concentration indicates that the chain termination process is predominantly bi-macromolecular. The temperature dependence on rate of precipitation polymerization obeys an Arrhenius equation with the activation energy found to be 21.49 kcal/mol. This result agrees well with the literature values of 23.5 and 22.0 kcal/mol obtained for the solution polymerization of partially neutralized acrylic acid (pH=11) and undissociated acrylic acid (pH=1), respectively. The weight average molecular weight of the polymer was found to be independent of conversion, indicating that transfer to the monomer is the chain controlling reaction.