Rapid Oxygen Tolerant Aqueous RAFT Photopolymerization in Continuous Flow Reactors

Recently, new controlled polymerization pathways have emerged for the synthesis of functional polymer materials. The use of light, particularly visible light, to generate radicals has shown to be beneficial over thermal induction due to the high control over reaction parameters as well as spatiotemporal control. Although numerous photopolymerizations have been performed in batch, additional initiators or activators are often needed to increase the overall yield, making this process time-consuming and costly; optical path lengths directly correlate with achievable space-time yields. The use of flow reactors is in this case advantageous. In this work, new synthetic protocols are demonstrated for the synthesis of di- and triblock copolymers in tubular reactors via photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization. Within just 10 min of polymerization time, full monomer conversion was reached for a variety of acrylamides and acrylates, and polymers with molecular weights up to 100000 g mol^–1 and high end-group fidelity were obtained. Changing the flow rates, concentrations, and light intensity allowed alteration of the molecular weights, and several di- and triblock copolymers were synthesized, indicating the high level of control over the polymerization. In addition, multiple flow reactors were coupled to allow the synthesis of triblock copolymers in a reactor cascade process without the need for intermediate purification. The attractiveness of this approach is illustrated by considering that a PDMAA-b-PDMAA-b-PDMAA triblock copolymer with a number-average molecular weight of 3200 g mol^–1 and dispersity of 1.24 could be theoretically obtained at a rate of 300 g/day.