Continuous Gas-Liquid-Solid Slug Flow for Sustainable Heterogeneously Catalyzed PET-RAFT Polymerization

Gas-liquid-solid (G-L-S) three-phase slug flow provides an efficient pathway to utilize solid catalysts in continuous flow and was adopted in the mesoporous graphite carbon nitride (mpg-C3N4)-catalyzed photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of methyl methacrylate (MMA) in this work. Kinetic studies and chain extension experiments illustrated the realization of reversible deactivation radical polymerization (RDRP) and the "easy to scale up" advantage of a continuous-flow reactor as compared to its batch counterpart. The light intensity played an important role on the PET-RAFT polymerization. An increasing amount of photocatalyst favored the monomer conversion within a limited range due to higher light blockage, and the monomer conversion reached a stable level at a lower catalyst concentration when higher light power was applied. When compared with fully continuous flow, the G-L-S slug flow was beneficial to the PET-RAFT polymerization due to the intensified swirling strength and narrower velocity field. Decreasing the gas-to-slurry ratio also led to narrower velocity distribution, which favored the polymerization as well. Moreover, the polymerization rates remained stable in multiple recycles, demonstrating that the present G-L-S slug flow was a reliable and easy processing approach for utilizing the solid catalyst.