The Role of Chain Transfer Agent in Reducing Branching Content in Radical Polymerization of Acrylates

Intramolecular transfer to polymer, and the reactions of the resulting midchain radical, are important processes in determining both the reaction kinetics and microstructure of acrylic polymers produced by radical polymerization. Herein, the causes of the reduction in branching content when adding chain transfer agent (CTA) to the polymerization mixture are unveiled. Quantitative NMR spectroscopy is used to determine the distribution of product species from the reaction of n-butyl acrylate in the presence of CBr4. It is shown that the reduction of branching is the result of the combined effect of a lower backbiting rate and the removal of the resulting midchain radical via transfer to CTA. The first effect is due to the minimum chain length required for backbiting to occur, and the second one is operative at high CTA/monomer ratios but becomes negligible at high concentrations of monomer.