The influence of mixing on chain extension by photo-controlled/living radical polymerization under continuous-flow conditions
Continuous-flow chemistry holds powerful potential for polymer synthesis, and has attracted increasing attention in recent years. Here, we demonstrate that mixing methods have clear impacts on chain-extension results (for example, molecular weight distribution = Đ) by photo-controlled/living radical polymerizations from macroinitiators under continuous-flow conditions exposing to visible-light irradiation. While the employment of a conventional mixer afforded block copolymers of broad molecular weight distributions (ca. Đ = 1.3–1.7), the utilization of a self-made packed plug gave copolymers of Đ = 1.2–1.3 (ca.), indicating that achieving a high homogeneity of combined streams is important to gain good control during chain-extension, especially for viscous polymer solutions. Facilitated with a packed plug, the flow synthesis of block copolymers has been successfully expanded to various monomers and macroinitiators, reactions with different flow parameters (for example, flow rate, concentration), and polymerizations at different [monomer]/[macroinitiator] ratios. These results show that an easily accessible and low-cost packed plug developed in this work could be used as an efficient and versatile mixing tool to facilitate polymer synthesis under flow conditions.