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Polyester polyurethanes are a major class of polymers, which are commonly used in coatings. The biodegradation mechanism of polyester polyurethane is complicated since it involves both biochemical and chemical catalysis to hydrolyze the polymers. Hence, finding the ideal pH sensitive probe that does not react with hydrolases and yet is reactive with either base or acid catalysts is crucial for differentiating the biodegrading regions from the chemically degrading regions. In this project, we report two diphenyl polyenes (DPPs), all trans-1,4-diphenyl-1,3-butadiene (DPB) and all trans-1,6-diphenyl-1,3,5-hexatriene (DPH) as potential pH sensitive probes suitable for polymer coatings. When exposed to trichloroacetic acid, DPPs undergo a visible color change and a red shift in their absorption spectra. We performed electronic structure and thermodynamic calculations to determine a possible site of protonation in the polyene moiety. We first calculated the electronic spectra and compared them to the absobance spectrum of the protonated DPPs. The gas phase calculations and spectroscopic titration data indicated that DPB is a somewhat stronger base than DPH. We then cast polyene blended polymer coatings (DPB and DPH were blended with poly(ethylenesuccinate) polyurethane coatings) and exposed each coating to a variety of strong acids (nitric acid, sulfuric acid, and hydrochloric acid) which resulted in decrease in fluorescence emission using fluorescence microscopy. Collectively, my results suggest that because of its greater solubility and basicity, DPB is potentially a more effective pH sensitive probe that DPH for observing acid diffusion during the degradation in polyester coatings.
Mark Masthay, Justin Biffinger
Shesham, Vaishnavi, "Assessing Diphenyl Polyenes as pH-Sensitive Colorimetric Probes of Proton Gradients in Polymer Coatings" (2021). Graduate Student Showcase. 22.