Use of a continuous-flow microreactor for thiol–ene functionalization of RAFT-derived poly(butyl acrylate)

Abstract

This study describes the synthesis of functionalized RAFT-derived poly(n-butyl acrylate) polymers via the use of a continuous-flow microreactor, in which aminolysis as well as thiol-ene reactions are executed in reaction times of just 20 minutes. Poly(n-butyl acrylate) (M n ¼ 3800 g mol À1, PDI ¼ 1.10) with a trithiocarbonate end group was prepared via a conventional RAFT process. The polymer was then functionalized via aminolysis/thiol-ene reactions in the micro-flow reactor with isobornyl acrylate, propargyl acrylate, poly(ethylene glycol) methyl ether acrylate and pentaerythritol tetraacrylate. To optimize the reaction time and reaction temperature of the micro-flow reactor, freshly collected samples were studied with soft ionization mass spectrometry. With this technique, efficient and very fast aminolysis and subsequent thiol-ene reactions take place on the RAFT-precursor polymer, yielding quantitative end group conversion within 20 min and functionalized polymers of 3700-4000 g mol À1, depending on the type of acrylate coupled. The use of a continuous-flow microreactor opens the pathway towards upsizing lab scale methods into larger processes without suffering from problems associated with reproducibility and tedious optimization issues.An often less valued key aspect of contemporary polymer synthesis, be it in the realm of controlled polymerization, click-like modifications or polymer analogous reactions, is the ability to upscale existing synthesis protocols. The adaption of procedures from microgram scale to significant production of materials on gram scale or larger is often tedious and accompanied with a loss in reaction efficiency or unreasonable reaction volumes. A convenient solution to this problem is the employment of microreactor technology.1 Miniaturized flow reactors offer the ability to optimize reaction conditions on a small scale while concomitantly allowing for simple upscale of reactions by going from small reactors to massive parallelization in reactor arrays or simply longer runtimes of the individual reactors. Also accelerations of the reactions can often be achieved by the rapid mixing of the components due to short diffusion lengths inside the microreactor, 2 as well as employing unconventional temperature regimes making microreactors in that respect comparable to the use of microwave reactors. The improved heat transfer of microreactors is a distinct advantage of these devices making their use especially interesting for highly exothermic reactions.3 While a wide array of commercial microreactors already exists, only a few studies have been reported so far on applications from the polymer field. Recently, Bally et al. described the synthesis of branched polymers from atom transfer radical polymerization (ATRP), 4 in a tubular microreactor. 5Also, polymerizations following the reversible addition fragmentation transfer (RAFT) 6 protocol have been described lately 7,8 as well as end group modifications 9 . Some earlier work on polymerizations in flow microreactors is summarized in a re...

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“…Hornung et al utilized a continuous flow tubular reactor as a scalable and convenient process for radical‐induced removal of the RAFT end groups at 100 °C in various organic solvents and water. Alternatively, Vandenberg and Junkers functionalized RAFT‐derived poly( n ‐butyl acrylate) polymers in a continuous flow microreactor via aminolysis and subsequent thiol–ene reaction with various acrylates as a model reaction to demonstrate the feasibility of large scale end group modification of RAFT‐derived polymers.…”