Investigation of novel photo-cross-linking reactions for the preparation of functional polymeric materials

Investigations of a number of photochemical cross-linking reactions are reported for the preparation of functional polymeric materials. Reactions that require constant inputs of light and do not proceed through radical or ionic mechanisms are studied, and the final properties of these materials are characterized. This work aims to expand the scope of available photo-cross-linking reactions for the preparation of functional materials. The incorporation of photodimerizable anthracene into a thermally healable vinylogous urethane copolymer enables light-induced post-polymerization UV cross-linking. This allows for tuning of the glass transition temperature over a 20 °C range, control over the rheological properties, and tuning the scratch healing temperature. Pendant attachment of anthracene moieties onto a flexible siloxane polymer (PDMS) results in macroscopic polymer crystallization upon photo-cross-linking, giving a heterogeneous material with up to 1 mm diameter crystallites embedded inside a flexible matrix. A thorough investigation of the growth of the polymer crystallites through microscopic and diffusion techniques revealed unique crystallite growth initiating from the bottom of the film and progressing upwards towards the irradiation source. The application of photogenerated singlet oxygen is applied to the cross-linking of amine siloxanes. Oxidative coupling of amine groups to imine groups results in facile cross-linking at room temperature in oxygen rich environments using visible light with no measurable side reactions. Solvent free precursors were prepared by covalent attachment of the sensitizer to the PDMS backbone. As coatings, these materials demonstrate contact antimicrobial activity against bacterial cells, being more effective against E. Coli than methicillin-resistant Staphylococcus aureus (MRSA), as well as inducing cell lysis in mammalian cells. This system was further developed as a dual-functional textile coating, utilizing both contact antimicrobial activity as well as photodynamic disinfection using singlet oxygen, which results in >99% bacterial disinfection in 90 minutes and a 10× decrease in SARS-CoV-2 viral infectivity in two hours. Singlet oxygen was also used to photo-cross-link thiol containing siloxanes through the oxidative preparation of a diaryl-telluroxide catalyst, effectively linking low thiol-content PDMS through disulfide formation. These polymers exhibit up to 400% elongation, and can be reductively cleaved back into liquids using NaBH4 with >90% mass recovery.Science, Faculty ofChemistry, Department ofGraduat