Characterization of Z-RAFT star polymerization of butyl acrylate by size-exclusion chromatography

Z-RAFT star polymerization of butyl acrylate using multifunctional trithiocarbonate-type RAFT agents carrying methyl propionate as the leaving group were used to form star polymers having 3, 4, and 6 arms. The polymerizations showed well controlled behavior up to high monomer conversions. By using a mixture of mono- and multifunctional RAFT agents, arm and star polymer were obtained simultaneously within a single RAFT polymerization, which enabled the evaluation of the apparent arm numbers. The desired topology of the star polymers was found being present already from the early phase of polymerization on. The apparent arm number slightly increases at very high monomer conversions in accordance to earlier reported star coupling reactions. Correction factors for conventionally calibrated SEC showed excellent agreement with data for polystyrene stars, indicating that the contraction of the hydrodynamic volume in comparison to linear polymer is only dependent on the polymer topology. The evaluation of absolute molar masses of star polymers was however limited by the accuracy of the conventional calibration.