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Authors: Rieger, Elisabeth
Title: Living anionic polymerization of activated aziridines
Online publication date: 26-Apr-2018
Year of first publication: 2018
Language: english
Abstract: This thesis is the first complete PhD thesis solely focusing on anionic polymerization of aziridines. A unique type of polyamines/ and polyamides with a wider range of functionalities is obtained, opening the possibility to novel exciting applications by a new building block for complex macromolecular architectures. The growing aziridine monomer family includes several functionalities and the monomers are mostly produced by efficient one- to three-step synthetic procedures. The polymerization kinetics for homo- and copolymerizations were studied by in situ 1H NMR spectroscopy. This methodology allows the online monitoring of the incorporation of monomer units into the growing polymer chains. Several solvents, counter ions and initiators were studied to reveal DMF and DMSO as the most suitable solvents. In contrast to oxyanionic, where lithium inhibits any chain growth, all counter ions, originated from alkali salts, were found to be appropriate. The novel azaanionic polymerization exhibited narrow monomodal molecular weight distributions in all cases and was proven to be living for several reaction conditions. Furthermore, it shows an enormous tolerance against protic impurities, like water and alcohols. Concentrations of these solvents, which would inhibit the other living anionic polymerizations immediately, were found to have almost no influence on the azaanionic polymerization. The secondary initiation by these impurities was below 10% in most cases, which is within the same range for controlled radical polymerization techniques. The nucleophilicity of the anions (chain ends and alkoxides) in reversed interaction with their pKa-values are considered as the main influencing factors, evaluated by DFT-calculations. These unique characteristics make the azaanionic polymerization highly promising for industrial applications due to its simpler handling and excellent control. The great variety of the different monomers has a big impact on a special feature of azaanionic polymerization, not achievable in other anionic polymerization to the same extent: sequence control in one-pot reactions. As the activating groups exhibit different electron withdrawing effects, they dominate the monomer reactivity. The ring-substituents, in turn, only show a negligible impact on the reaction kinetics, due to steric hindrance. The stronger the electron withdrawing effect of the activating group, the faster it reacts, which is reflected in the determined electrophilicity indices. This offers new possibilities to tune the final microstructure of copolymers, as tailored random, gradient and block copolymers are afforded in a closed system one-pot reaction, without further monomer addition. These copolymerizations were also monitored using real-time NMR-spectroscopy, allowing the simultaneous copolymerization of up to five monomers for the first time. This allows the precise installation of functional groups along the polymer backbone (sequence control), just by the selection of different starting monomers with respective reactivities. Next to the intrinsic reactivity of the monomers, also their physical properties, such as their different solubility profiles, offers another strategy to alter the copolymerization behavior. A monomer pair with identical activating groups but ring-substituents of different hydrophobicity exhibit the same chemical reactivity and lead to an ideal random copolymer in solution. However, these two monomers can be physically separated in an emulsion system, where the hydrophobic monomer prefers the continuous cyclohexane phase over the dispersed DMSO-phase, which contains mainly the hydrophilic monomer. As the copolymerization is exclusively constricted to the DMSO-phase (compartments), gradient to block-like structures are obtained, just by simple separation and respective dilution of the continuous phase, which adjusts the strength of the gradient. As the application of polyaziridines themselves is still in its very early stages, their manifest value lies in the use of their desulfonylated version as polyamines. LPEI is to date the most efficient transfection agent, but it is also very toxic. Consequently, the research on alternatives continues and polyaziridines represent a potential new option. Nevertheless, the use of polyaziridines as LPEI precursors is particularly advantageous because of their better polymerization control. Therefore, two deprotection strategies for the desulfonylation of polyaziridines are presented within this work, to reveal new alternatives for LPEI and its applications as a polyelectrolyte. In summary, this is the first thesis focusing solely on the living anionic polymerization of aziridines, which proves them as powerful building blocks for future macromolecular architectures. Tuning functional group density along a polyamide/polyamine backbone provides a wide range of new materials with manifold functionalities and properties.
DDC: 540 Chemie
540 Chemistry and allied sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
Place: Mainz
URN: urn:nbn:de:hebis:77-diss-1000019684
Version: Original work
Publication type: Dissertation
License: In Copyright
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Extent: 364 Seiten
Appears in collections:JGU-Publikationen

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