Responsive and biodegradable hydrogels from radical ring-opening polymerisation of CKAs and their in-depth characterisation using advanced light scattering and fluorescence

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Radical Ring-Opening Polymerisation (RROP) of cyclic ketene actals (CKAs) has gained increasing attention as tool to generate novel polyesters as biodegradable polymers. This project will see their expansion into polymer networks to generate pH-responsive and fully biodegradable hydrogels based on the hydrophilic polyester from the CKA 2-methylene-1,3,6-trioxocane (MTC). In light of our recently reported amine-bearing CKA, which produces pH sensitive polyesters, pH-sensitive hydrogels are now in reach with RROP. In order to assess the full scope of RROP-based hydrogels, we will assess a bis-CKA without amines, a new amine-bearing bis-CKA as well as a methacrylic cross-linker. The latter will be an important benchmark substance to assess the quality of the CKA-based cross-linkers. A broad range of pH responsive and non-responsive hydrogels will be synthesised over the course of the project, underlying our efforts to establish RROP in the field of hydrogels. Following their synthesis, the gels will be thoroughly characterised using state-of-the-art dynamic and static light scattering techniques. Together with rheology and fluorescence-based analysis, mesh-sizes, inhomogeneities on the micro- and nanoscale as well as the diffusion behaviour of guest substances within the hydrogel will be assessed. Inhomogeneities will yield insights into the reactivity of the cross-linkers to provide direct feedback to the synthetic efforts in order to optimise the synthetic strategy. Together with the fluorescence methods to assess diffusion properties, the pH responsive behaviour with its micro- and macroscopic changes of the gel will be analysed in-depth. Rheology and light scattering will also be used to confirm the stability of the polyester-gels at ambient conditions. Following this full-scale analysis of the hydrogels, they will undergo a complete degradation triggered by the addition of esterase. Degradation will be monitored using a similar array of methods as the intact hydrogels to get insights into the micro- and macroscopic changes of the gels during degradation. Rheological assessments during degradation will allow to determine when the gel point has been breached and the gels have been destroyed. However, degradation will continue further until no oligomeric residues are left over. The final small molecules will be analysed to confirm a complete degradation but also to confirm the expected structure of the final hydroxy-acids. Altogether, this project will see the introduction of a broad array of hydrogels based on RROP, their full-scale analysis using rheology, light scattering and fluorescence methods, followed by their degradation. This will be key to get a deeper understanding of RROP and to establish it further in the field of polymer chemistry.