Continuous-Flow PET-RAFT Polymerization in a Packed-Bed Reactor with Porphyrin-Immobilized Silica Particles

Photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization enables the production of well-controlled synthetic polymers under mild conditions by using visible-light energy. Although flow reactors are suitable for photoreactions in terms of light penetration, contamination of photocatalysts occurs in a homogeneous system and necessitates product purification. Immobilizing the photocatalysts onto supports can eliminate the need for this purification step and enhance the potential for industrial applications of PET-RAFT polymerization. Herein, we report the development of a packed-bed flow photoreactor wherein a photocatalyst for PET-RAFT polymerization, zinc tetraphenylporphyrin, was immobilized onto packed silica particles. Continuous PET-RAFT polymerization of a model monomer (N,N-dimethylacrylamide) was achieved without leakage of the porphyrin molecules. The effects of various reaction conditions, such as the residence time, catalyst density, and target molecular weight, on the polymerization reaction were evaluated. This work contributes to the realization of a facile and practical manufacturing process for highly valuable synthetic polymers.