Divergent Synthesis of Graft and Branched Copolymers through Spatially Controlled Photopolymerization in Flow Reactors

Abstract

In this work, we demonstrate the controlled synthesis of graft and branched copolymers using one-pot (batch) or one-pass (flow) processes without intermediate purification. The formation of poly(methacrylate) copolymers with pendent reversible addition–fragmentation chain transfer (RAFT) agent functionalities was performed using a selective photoactivation approach in the first step, specifically via green light-mediated direct photoRAFT polymerization. A nonselective photoinduced chain extension using red light-triggered photoinduced energy/electron transfer (PET)-RAFT polymerization was then performed to provide tailored graft copolymers. Notably, the application of this protocol to a flow process with two spatially segregated unit operations provides a route to independent control of the backbone-forming step (unit operation one) and the subsequent chain extensions (unit operation two). By alternating the light sources in both unit operations between the On and Off states, a range of macromolecular architectures could be prepared from the same starting materials. To demonstrate the power of this divergent approach, a series of graft copolymers with tailored backbone lengths and number and molecular weight characteristics of side chains were synthesized using the same starting materials by a single pass process. Additionally, the polymer architecture was switched between graft and hyperbranched architectures via external manipulation of light sources.