Effect of solvent on the rate constants in solution polymerization. Part I. Butyl acrylate

An experimental study was performed to estimate the value of the lumped kinetic constant kp/k. This quantity was evaluated using the well-known conversion vs. time approach in dilute solutions using both azo-bis-isobutyronitrile and benzoyl peroxide (AIBN and BPO), and two different solvents (toluene and ethyl acetate) at 60°C. It was demonstrated that if one uses the classic model for homopolymerization kinetics, the value of the lumped rate constant depends very strongly on the concentration of the monomer in the solution, decreasing as the solution becomes more and more dilute. This result was observed for both initiators and both solvents, and found to be independent of initiator type, but slightly more pronounced for toluene than for ethyl acetate. The number- and weight-average molecular weights of the different polymers were also measured, and excellent agreement was found between the measured and modeled values. It was demonstrated that there was a practically linear relationship between the value of the lumped constant and the square root of the number-average chain length.