Development of Novel Polymeric Sunscreens

Abstract

This dissertation details the preparations and investigations of novel polymeric sunscreen agents as alternatives to commercial chemical and mineral sunscreens. In addition, results obtained from an investigation into the efficacy and photostability of North American commercial sunscreens are also reported. Based on the discoveries made during the research studies, two new classes of polymeric sunscreen agents with excellent broad-spectrum photoprotections and photostabilities are reported. The first chapter is a comprehensive review discussing the classifications of sunscreen agents, their photoprotective mechanisms, benefits, limitations, safety concerns, cosmetic additives utilized in the manufacturing process, as well as the types of formulations used during product development. Methods developed and regulatory requirements for evaluating the broad-spectrum efficacy of sunscreen agents, their photostability, and immunosuppression protection were also discussed. This chapter provides the context necessary for understanding commercial sunscreens investigated in chapter two and the in vitro broad-spectrum photoprotective efficacy evaluations conducted in chapters two, four, and five. In Chapter 2, the findings of a research study investigating the UV photostability and efficacy of 20 commercial sunscreens with SPF 50 labels are reported. The commercial sunscreens involved 10 chemical and 10 mineral non-prescription sunscreens currently available on the North American market. The UVB and UVA efficacy changes were evaluated using in vitro methods as a function of UV exposure using simulated sunlight. A research study investigating the efficacy of commercial sunscreens at this scale had not been conducted for the North American region prior to the author’s study, making it unique. Chapter 3 is an up-to-date comprehensive review summarizing and evaluating the academic publications and invention disclosures related to polymeric sunscreen research. This chapter educates the reader on the advancements made in the field of polymeric sunscreens. It supplies the required context for understanding the novel macromolecular sunscreen materials developed and investigated in chapters four and five. Polymeric sunscreens were categorized as natural biopolymer-based or synthetic polymer-based on their derived source, and their preparation, formulation, and assessment of broad-spectrum photoprotective efficacy and UV stability were summarized and critiqued. The advantages of using polymeric photoprotective agents over existing commercial chemical and mineral sunscreens were also discussed. The author also analyzed biocompatibility, environmental impacts, and commercial implementation costs of these photoprotective macromolecules for value-added applications. Chapter 4 reports on the development of a new class of polymeric sunscreen agents comprised of phenolic-higher aldehyde thermoset resin spheres synthesized using a base-catalyzed polycondensation technique under hydrothermal conditions. These thermoset resin-based sunscreens are water-resistant, absorb and scatter broad-spectrum UV radiation, provide excellent UV skin protection, and have enhanced stability to UV-induced photodegradation. The photodegradation effects of phenolic-aldehyde thermoset resins were evaluated using IR spectroscopy and SEM techniques, and photodegradation mechanisms were discussed. Chapter 5 disclosed novel antioxidant, broad-spectrum polymeric sunscreens synthesized by post-polymerization click modification of polybutadienes with three distinct s-tetrazines. The polydihydropyridazines synthesized using click modifications were hydrophobic, antioxidant, provided excellent broad-spectrum UV protection, and were fluorescent active. Quenching of fluorescence was seen with chemical or photooxidation of polydihydropyridazines to polypyridazines, along with a loss of antioxidant activity and photoprotective effect. Loss of fluorescence activity provides a visual tool for qualitative monitoring of the extent of photooxidation of polydihydropyridazine sunscreen polymers. Photooxidative degradation of polydihydropyridazine thin films exposed to UV radiation was monitored using 1H NMR and IR spectroscopy. The antioxidant activity of polydihydropyridazines was evaluated using cyclic voltammetry. Finally, Chapter 6 summarizes the research conducted in chapters two, four, and five and provides future research ideas to address the shortcomings of current work.