Continuous Flow Synthesis of Core Cross-Linked Star Polymers via Photo-Induced Copper Mediated Polymerization

Abstract

A convenient method to synthesize core cross-linked star polymers via a continuous flow photopolymerization process is developed. Photo-induced copper mediated radical polymerization was employed for arm and star synthesis. The arms of the core cross-linked star polymers are composed of poly(methyl acrylate) (with Mn, arm of 2600 or 4700 g·mol-1 , Đarm ≈ 1.12) and 1,4-butanediol diacrylate was used as core cross-linker. Flow polymerization enables rapid formation of star polymers (15-20 minutes, Mw, star flow = 170 400 g·mol-1, 33 arms). Further, a reactor cascade was build that combines arm synthesis and star synthesis without isolation of the intermediate product between both reactor stages. In this way star polymer is formed (Mw, star = 156 500 g·mol-1, 34 arms) in a one-pot fashion, yet under scalable conditions. Surface functionalized star polymers were obtained with similar molecular weights via alcohol-functional initiators. Finally, a flow reactor setup is demonstrated that allows for direct access to miktoarm star polymers. In there, two different arms are synthesizied from photopolymerization in parallel and then simultaneously fed into a third reactor. The resulting miktoarm core cross-linked star polymers composed of poly(methyl acrylate) and poly(benzyl acrylate) arms (Mw, star = 189 300 g·mol-1, 33 arms). The reactor cascade enables rapid star polymer formation in a continuous process (within 40 minutes, when reactor conditions are stable) without intermediate purification, improved illumination and facile upscaling.