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 syntheses. The arms of the core cross-linked star polymers are composed of poly(methyl acrylate) (with a M_{n, arm} of 2600 or 4700 g mol⁻¹, Đ_arm ≈ 1.12), and 1,4-butanediol diacrylate was used as the core cross-linker. Flow polymerization enables the rapid formation of star polymers (15–20 minutes, M_{w, star flow} = 170 400 g mol⁻¹, 33 arms). Furthermore, a reactor cascade was built that combines arm and star syntheses without the isolation of the intermediate product between both reactor stages. In this way, the star polymer is formed (M_{w, 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 direct access to miktoarm star polymers. In there, two different arms are synthesized from photopolymerization in parallel and then simultaneously fed into a third reactor. The resulting miktoarm core cross-linked star polymers are composed of poly(methyl acrylate) and poly(benzyl acrylate) arms (M_{w, 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.