Amphiphilic block copolymers via blue-light-induced iniferter RAFT ab initio emulsion polymerization in water-alcoholic media

Abstract

Amphiphilic block copolymers comprise a fascinating class of smart materials due to their unique ability to self-organize, making them attractive candidates for a wide range of applications in materials engineering and medical sciences. The synthesis of these copolymers commonly involves harmful solvents, especially in classical living anionic polymerization. With the development of reversible addition–fragmentation chain transfer (RAFT) and polymerization–induced self-assembly (PISA), an environmentally more friendly and versatile method has been established for the synthesis of such amphiphilic block copolymers. Through the utilization of visible light to initiate polymerization through the so-called photoiniferter process, we emphasize the adaptability of this photopolymerization in different scales although the incident light illuminates only the surface area of the reaction vessels. We describe an easily adjustable, blue-light-initiated RAFT PISA approach to synthesize a series of amphiphilic poly(N,N-dimethylacrylamide)–block–polystyrene (PDMA–b–PS) and poly(4-vinylpyridine)–block–polystyrene (P4VP–b–PS) diblock copolymers with low molecular weight dispersities. The polymerizations were conducted as both two-step and semibatch processes. Furthermore, the effect of scalability on the polymerization kinetics was investigated, proving the light-induced RAFT polymerization as a scalable polymerization method in a batch process with a reaction volume of up to 500 mL. The bulk morphology of both resulting diblock copolymers having different weight fractions of the minor and major blocks was analyzed. While a cylindrical PDMA microdomain in a PS matrix can be observed at 20–25% by weight of PDMA, the equivalent composition reveals a spherical morphology of P4VP domains in a PS matrix. In essence, the scalable, rather eco-friendly photoinduced synthesis of tailored, nanostructured block copolymers without harmful solvents significantly increases their suitability for applications.