Viscosity Function of a Fast Reactive Polymerization-Aqueous Solution of Acrylic Acid in a Rheometer

The focus of this research is a special technique to investigate the polymerization of the water soluble monomer acrylic acid in a rheometer. The rheokinetics is an approach to measure the viscosity of reactive solutions during polymerization and consequently monitor the reaction kinetics. Results are presented on the initial stage of acrylic acid polymerization in water at different temperatures, 50, 60, and 70 degrees C with mass fractions between 12.5% and 35% and two different initiator ratios, 0.8 and 1.2 mmol/mol. An empirical viscosity model to describe the shear viscosity over time is available. With reaction kinetics from literature and the viscosity model, a determination of the exponents a and b of a rheokinetics model is undertaken; a is 1.5 and b is 1.9-2.8. Further investigations show that it is possible to analyze the monomer conversion at a certain time when quenching the reaction and measure the polymer concentration. With the use of a simple reaction model, the conversion is calculated like in a batch reactor, representing the gap in the rheometer. Differences with the stepwise measured conversions are not very high. A rheokinetics approach is consequently useful for optimizing processes, where fast reactions in a continuous flow are present. (C) 2016 Society of Plastics Engineers