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Polyorthoesters and analogues from a cyclic ketene acetal as surface-erodible materials in additive manufacturing and elastomer fabrication
Summary
This thesis describes the synthesis and manufacture of novel biodegradable poly(orthoester-thioether) polymers using stable orthoester monomers and thiol-ene chemistry. The materials were designed as surface-erodible alternatives for applications in additive manufacturing and elastomers, potentially reducing the environmental persistence of plastic components.
Motivated by the advantageous rapid surface-erosion behaviour but problematic manufacturing of pure polyorthoesters (POE), in this thesis, the synthesis and manufacturing of poly(orthoester-thioether) (POETE) materials from stable orthoester (OE) monomers via thiol-ene Michael addition are described. Initially, a variety of novel OE compounds was synthesised and comprehensively characterised, followed by UV-initiated thiol-ene coupling with a selection of thiols. The full scope of OE-TE compounds ranged from small molecules over POETE polymer chains and networks, to the use of POETEs as soft segments in polyurethanes (PUs).Subsequently, chromatographic, spectroscopic and microscopic, as well as thermo-mechanical analyses were performed in order to facilitate conclusions on the structure/composition-function relationship, as well as to further investigate the degradation process. Chapter 1 provides an introduction into the importance, synthesis and degradation properties of polymers like POEs and elastomers such as polyurethanes (PUs), as well as principles of rapid additive manufacturing to process polymers for direct application, as used in the rest of the work. Chapter 2 details the synthesis of simple OEs, acetals (ATs) and the respective thioethers (TEs) in the form of small molecules and chain polymers, including their comprehensive spectroscopic and chromatographic analysis. The method is then used to produce a strong network material, on which subsequent surface erosion behaviour is documented and degradation products investigated. Chapter 3 offers an overview of a library of new OE monomers and their spectroscopic properties, as well as comprehensively displays the thermo-mechanical properties of a variety of network materials obtained by crosslinking the OEs with multifunctional thiols. In addition, the results of 3D printing, degradation and cytocompatibility studies are presented. Chapter 4 introduces a strategy to manufacture poly(thio-urethanes) from POETE oligomers and demonstrates that hydrolytically degradable, strong and elastic, glassy and semi-crystalline materials can be obtained. Chapter 5 summarises the work reported in Chapters 2 to 4 and advises on future perspectives, optimisations and potential applications.