Elisabeth Rieger

Sequence-Controlled Polymers via Simultaneous Living Anionic Copolymerization of Competing Monomers.

Natural macromolecules, i.e., sequence-controlled polymers, build the basis for life. In synthetic macromolecular chemistry, reliable tools for the formation of sequence-controlled macromolecules are rare. A robust and efficient chain-growth approach based on the simultaneous living anionic polymerization of sulfonamide-activated aziridines for sequence control of up to five competing monomers resulting in gradient copolymers is presented. The simultaneous azaanionic copolymerization is monitored by real-time (1) H NMR spectroscopy for each monomer at any time during the reaction. The monomer sequence can be adjusted by the monomer reactivity, depending on the electron-withdrawing effect by the sulfonamide (nosyl-, brosyl-, tosyl-, mesyl-, busyl) groups. This method offers unique opportunities for sequence control by competing copolymerization: a step forward to well-engineered synthetic polymers with defined microstructures.

N-Ferrocenylsulfonyl-2-methylaziridine: the first ferrocene monomer for the anionic (co)polymerization of aziridines

N-Ferrocenylsulfonyl-2-methylaziridine (fcMAz) is synthesized in a convenient three-step protocol from ferrocene. It represents the first aziridine-based monomer suitable for the anionic polymerization, carrying a ferrocenyl-substituent. Sulfonamide-activated aziridines can undergo (mostly living) anionic polymerization and fcMAz is also the first example of a functional sulfonamide-based aziridine monomer. It can be polymerized with different initiators to homo and copolymers (block or statistical) with adjustable molecular weights. The homopolymer is insoluble in common organic solvents, while the copolymers with other aziridines are soluble and exhibit molecular weight dispersities of 1.1–1.5. FcMAz thus broadens the scope of ferrocenyl-containing polymers and may be combined with other anionic polymerization techniques in the future.

Controlling the Polymer Microstructure in Anionic Polymerization by Compartmentalization

An ideal random anionic copolymerization is forced to produce gradient structures by physical separation of two monomers in emulsion compartments. One monomer (M) is preferably soluble in the droplets, while the other one (D) prefers the continuous phase of a DMSO-in-cyclohexane emulsion. The living anionic copolymerization of two activated aziridines is thus confined to the DMSO compartments as polymerization occurs selectively in the droplets. Dilution of the continuous phase adjusts the local concentration of monomer D in the droplets and thus the gradient of the resulting copolymer. The copolymerizations in emulsion are monitored by real-time 1 H NMR kinetics, proving a change of the reactivity ratios of the two monomers upon dilution of the continuous phase from ideal random to adjustable gradients by simple dilution.

Fast Access to Amphiphilic Multiblock Architectures by the Anionic Copolymerization of Aziridines and Ethylene Oxide

An ideal system for stimuli-responsive and amphiphilic (block) polymers would be the copolymerization of aziridines with epoxides. However, to date, no copolymerization of these two highly strained three-membered heterocycles had been achieved. Herein, we report the combination of the living oxy- and azaanionic ring-opening polymerization of ethylene oxide (EO) and sulfonamide-activated aziridines. In a single step, well-defined amphiphilic block copolymers are obtained by a one-pot copolymerization. Real-time 1H NMR spectroscopy revealed the highest difference in reactivity ratios ever reported for an anionic copolymerization (with r1 = 265 and r2 = 0.004 for 2-methyl- N-tosylaziridine/EO and r1 = 151 and r2 = 0.013 for 2-methyl- N-mesylaziridine/EO), leading to the formation of block copolymers with monomodal and moderate molecular weight distributions ( Mw/ Mn mostly ≤1.3). The amphiphilic diblock copolymers were used to stabilize emulsions and to prepare polymeric nanoparticles by miniemulsion polymerization, representing a novel class of nonionic and responsive surfactants. In addition, this unique comonomer reactivity of activated-Az/EO allows fast access to multiblock copolymers, and we prepared the first amphiphilic penta- or tetrablock copolymers containing aziridines in only one or two steps, respectively. These examples render the combination of epoxide and aziridine copolymerizations via a powerful strategy for producing sophisticated macromolecular architectures and nanostructures.