Researcher(s)
- Tetsutaro Maeda, Physics, Reed College
- Casey Cox, , University of Delaware
Faculty Mentor(s)
- LaShanda Korley, Materials Science & Engineering, University of Delaware
Abstract
Polyurethanes (PUs) exhibit versatile material properties and are often employed for applications in a range of different environments, including those with high UV exposure and humidity. Nevertheless, such conditions can promote free-radical UV degradation of PUs, impacting their performance and contributing to negative environmental and health impacts over time. Polyhydroxyurethanes (PHUs), synthesized from cyclic carbonates and amines, offer a more sustainable alternative to conventional PUs by avoiding the utilization of hazardous isocyanate precursors. The bicyclic, aliphatic structure of citric acid-derived octahydro-2,5-pentalenediol (OPD) and its derivatives can be leveraged to synthesize cyclic carbonates for the design of fully aliphatic PHUs, which may exhibit superior UV resistance compared to aromatic-containing PHUs, without compromising mechanical performance. While aliphatic polymers possess excellent baseline UV stability due to the lack of unsaturated bonds, additives such as hindered amine light stabilizers (HALS) are still commonly added to mitigate the propagation of UV degradation.
In this work, we investigate the effects of UV exposure on the physical properties of OPD-based PHUs, both with and without HALS end-functionalization. The chemical structures as well as the optical, thermal, and mechanical properties of OPD PHUs will be characterized before and after being subjected to weathering conditions (i.e., cyclical exposure to UV irradiation in a heated UV chamber followed by exposure to heat and moisture in a condensation chamber). It is anticipated that HALS incorporation into PHUs will improve UV stability, evaluated by the retention of optical properties (e.g., yellowness index) and thermal and mechanical properties (e.g., glass transition temperature, tensile strength, elongation-at-break, Young’s modulus). Additionally, the impact of HALS incorporation on changes in chemical structure will be monitored via Fourier transform infrared spectroscopy. Overall, this work seeks to improve the UV stability of PHU materials by leveraging the aliphatic structure of citric acid-based compounds and incorporating HALS via hydroxyurethane chemistry.