Alcohol-based PISA in batch and flow: exploring the role of photoinitiators

Abstract

Polymerization-induced self-assembly (PISA) via PhotoRAFT (photoinduced reversible addition-fragmentation chain transfer) in less polar solvents via continuous flow reactors was investigated. At first, a batch protocol was designed for the activation of the trithiocarbonate-derived poly(oligo ethylene glycol methacrylate) (POEGMA) macroRAFT under blue light in the presence of benzyl methacrylate (BzMA). A variety of solvents, photoinitiators as well as light intensities were tested, leading to improved reaction conditions in batch. With the optimized batch protocol, POEGMA-b-PBzMA particle synthesis was adapted for flow processing, demonstrating the potential of continuous tubular reactors for the synthesis of nanoparticles with different morphologies via alcoholic RAFT dispersion PISA. As the addition of various photoinitiators did not lead to the anticipated increase in polymerization rate, we further investigated the initiation mechanism using (meth) acrylates. POEGMA as well as the acrylate-based analogue (POEGA) were chain extended using different acrylates/methacrylates under photoiniferter and photoinitiation conditions. Due to the weaker C-S bond of the methacrylate-based macroRAFT, the additional generation of radicals from the photoinitiator TPO had less significant impact on the polymerization rate than for the acrylate-based macroRAFT, which underwent much slower photoiniferter activation. Methacrylate-based macroRAFT was converted into an acrylate-based macroRAFT when extended with acrylate monomer, thus explaining why this particular case does lead to a rate increase in addition of TPO, unlike for the extension with a methacrylate.