Understanding dispersity control in photo‐atom transfer radical polymerization: Effect of degree of polymerization and kinetic evaluation

Abstract

AbstractIn photo‐atom transfer radical polymerization (ATRP), dispersity can be efficiently controlled by varying the deactivator concentration. In this work, we provide mechanistic insight into dispersity‐controlled photo‐ATRP by conducting detailed kinetics under a range of conditions. For the lower dispersity polymers, a conventional first‐order kinetic profile was observed accompanied by a linear evolution of number average molecular weight (Mn) with conversion while the reactions reached moderate to high conversions (between 66% and 93%). Whereas, when polymers of high dispersity were targeted, the Mn remained relatively constant throughout the polymerization and the reactions ceased at less than 50% of conversion. In particular, for Ð = 1.84, a significant deviation between theoretical and experimental molecular weights was evident. This deviation was unambiguously attributed to slow initiation as indicated by 1H NMR, where significant percentages of unreacted initiator were observed. Importantly, the addition of ligand at the polymerization plateau re‐initiated the polymerization and led to the complete consumption of the unreacted initiator, thus enabling the synthesis of one‐pot diblock copolymers. We subsequently evaluated the effect of the degree of polymerization (DP) on the obtained dispersity when a constant catalyst ratio was maintained. Based on the interpolation of those experiments results, we could predict experimental conditions for any desirable DPs and dispersities.