Design and synthesis of application-oriented polyethers via introduction of nitrogen, fluorine or boron
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Abstract
This work deals with the design, synthesis, and characterisation of application-oriented multifunctional polyethers. To this end, state of the art concepts in the areas of transfection agents, hydrate inhibitors, surface active polyfluoro-compounds, and organoborane compounds as polymerisation catalysts were developed further and applied in form of polyethers.
Beginning with the theoretical background of this work, section 1 first gives a brief introduction to polyethers and their, for this work relevant, synthesis strategies. The use of organoboranes in catalytic polymerisations and their chemical versatility is discussed. In the following, further targeted applications of in this work developed polymers are introduced. This part deals on the one hand with polyelectrolytes as cationic transfection agents as well as kinetic hydrate inhibitors (KHI) in fluid applications. On the other hand, organofluorine compounds are presented in the context of their properties, ecological risks, current development, and their application as surfactants as well as surface coatings.
Section 2 deals with amino-functional polyethers and is divided in their application as transfection agent and as KHI.
Chapter 2.1 investigates poly(glycidyl amine)s in a biomedical context. Series of copolymers with increasing ratio of amino-functionalities were synthesised via copolymerisation of ethylene oxide (EO) and a variety of glycidyl amines. This procedure enables adjustment of the amino group density and as a direct consequence the adjustment of the charge density, which is an important factor for transfection agents. Subsequently, the polymers toxicity as well as their abilities to complex desoxyribonucleic acid (DNA), transfer it into cells and allow protein synthesis were studied. The efficiency of complexation and transportation into cells increased with decreasing size of the amine substituents. Nonetheless, the ultimate aim of protein biosynthesis using the transfected DNA was not achieved with this system.
Chapter 2.2 introduces poly(glycidyl amine-N-oxide)s (PGAO) as kinetic hydrate inhibitors and chapter 2.3 develops this concept further by studying the structure-activity relationship of a variety of substituents. Both chapters begin with the synthesis of PGAO via anionic ring-opening polymerisation (AROP) and subsequent oxidation. Chapter 2.3 additionally introduces azepane glycidyl amine as a monomer for AROP. The PGAOs ability to delay gas hydrate formation and to decrease their growth rate was studied utilising a high-pressure rocking rig and a structure II hydrate-forming gas mixture. Chapter 2.2 focusses on diethylamino- and the 6-membered piperidine substituents and compares KHI-activities of homo- and blockcopolymer with polypropylene oxide as a synergistic block. Chapter 2.3 studies the influence of the substituent´s ring size (5- to 7-membered) as well as of the initiator (aromatic or aliphatic) and the necessity of the amine-oxidation itself.
Section 3 presents a collaboration with the German company Merck KGaA regarding surface active polyethers, which bear degradable polyfluorinated side chains. Utilising the monomer activated anionic ring-opening polymerisation (MAROP), series of copolymers derived from epoxides bearing the polyfluorinated side chain and either hydrophilic or hydrophobic epoxides were synthesised. This yielded on the one hand amphiphilic surfactant structures, which were studied for their ability to reduce the surface tension of water. On the other hand, omniphobic copolymers were gained, which were used to coat surfaces and were studied for their repellency of liquids. Furthermore, their thermal properties were studied. Systematic variation of the comonomer ratio allowed tuning of the surface activity properties. In situ 1H NMR kinetic studies revealed a weak gradient in the polymer microstructure.
In regard to the MAROP used in the previous section, section 4 studies organoborane bearing polyethers as alternative polymerisation catalysts. Initially, double bond bearing polyethers were synthesised via AROP. These double bonds were used in hydroboration reactions to yield either boronic esters or dialkylboranes. Acidic cleavage of the boronic esters yielded boronic acids, a versatile functional group. The dialkylborane bearing polyethers were studied as a polymeric alternative of small molecule aluminium or borane catalysts in polymerisations. The scope of the polymeric catalysts was examined by synthesising amorphous poly(propylene oxide) and crystalline poly (epoxytetradecane) as representatives of polyethers as well as poly(cyclohexane carbonate). Furthermore, the recyclability of the catalyst was demonstrated.