Matthias Conradi

Photo-induced copper-mediated polymerization of methyl acrylate in continuous flow reactors

Photo-induced copper-mediated radical polymerization of methyl acrylate (MA) is carried out in DMSO at 15 °C in a tubular photo-flow reactor as well as in a glass-chip based microreactor. Polymerization reactions proceed rapidly to approximately 90% monomer conversion within 20 minutes of reactor residence time. Control of reactions is high as evidenced by ideal polymerization kinetics, low dispersities of the obtained polymers (in the range of 1.1) and linear evolution of number average molecular weights during polymerization reactions. Poly(MA) with average molecular weights between a few hundred and ∼5000 g mol−1 was obtained under retention of pristine end group fidelity. Besides homopolymers, block copolymers can also be successfully synthesized and poly(methyl acrylate)-b-poly(butyl acrylate) block copolymers with a similar low dispersity are obtained. Reactions proceed under homogeneous reaction conditions. This feature allows the reaction to be carried out in milli- and also in microflow devices. In both cases, equally good control is achieved with only minimal adaptation of the reaction protocol, underpinning the simplicity and fast adaptability of the protocol to different flow reactors.

Enhanced Spin-capturing Polymerization and Radical Coupling Mediated by Cyclic Nitrones

A series of cyclic nitrones have been tested for their spin-trapping activity in the enhanced spin-capturing polymerization of styrene and in nitrone-mediated radical coupling reactions. rac-2-Isopropyl-2,3-dimethyl-1-oxy-2,3-dihydro-imidazol-4-one was found to be the most efficient nitrone. The specific polystyrene macroradical addition rate to this nitrone was determined to be 8.0 × 103 L mol–1 s–1, which is by a factor of 10 higher than for previously studied compounds. Via enhanced spin-capturing polymerization, polymers in the range of oligomers to 30000 g mol–1 were obtained. A strong dependence of molecular weight on monomer conversion was observed, which can be explained by the high trapping rate. In nitrone-mediated radical coupling, almost ideal coupling of bromine-functional polymers was obtained and the successful introduction of the residual alkoxyamine functionality confirmed.

UV-induced functionalization of poly(divinylbenzene) nanoparticles via efficient [2 + 2]-photocycloadditions

The efficient functionalization of poly(divinylbenzene) (polyDVB) nanoparticles via Paterno–Buchi type [2 + 2]-photocycloadditions is described. Initially polyDVB nanoparticles with high density of alkene groups on the surface are synthesized via radical miniemulsion polymerization. Subsequently, UV-induced [2 + 2]-photocycloadditions with different functionalized aldehydes have been performed on the surface under mild and catalyst-free conditions. In order to show the versatility and the accessibility towards incorporation of different functionalities with this strategy, surface modifications were carried out with ATRP initiators and NHS esters for bioconjugation, respectively. Finally, these photofunctionalized nanoparticles were grafted with poly(butyl acrylate) or with gold-labeled antibodies to prove the success of the reactions. PolyDVB nanoparticles before and after photofunctionalization are characterized by X-ray photoelectron spectroscopy (XPS), electron microscopy (SEM and TEM) and ATR-FTIR spectroscopy. Results show that the photoconjugation route is highly efficient and grafting densities of 4 to 5 molecules per nm2 on the entire surface of the particles are achieved.