Investigation of color formation and H2O2-assisted decolorization in CO2-derived polyhydroxyurethane

Abstract

CO₂-derived polyhydroxyurethane (PHU), synthesized via the aminolysis of cyclic carbonate, faces limitations in replacing conventional polyurethane (PU) for color-sensitive applications due to its yellow color. In this study, we investigate, for the first time, the coloration pathways in PHU and explore the use of hydrogen peroxide (H₂O₂) to eliminate polymer color. Model compounds, resembling a PHU repeating unit, are prepared from CO₂-derived bis(cyclic carbonate) and monoamines and then thermally aged to trace the color-forming species. Observations of the changes in Fourier-transfer infrared spectroscopy and mass spectrometry indicate multi-pathway thermal oxidation to occur at both the nitrogen-vicinal and the oxygen-vicinal methylene carbon adjacent to the urethane linkage. The changes track well with an increase in the model compound's color index as determined from UV–visible spectra, providing an explanation for PHU's susceptibility to coloration. The colored model compound and PHU are then subjected to H₂O₂ treatment to disrupt the conjugated carbonyl groups and thus reduce the color. Parameters, including H₂O₂ concentration, treatment time, and temperature, are examined for a linear PHU system, and a set of optimized treatment conditions are implemented to yield PHU with reduced color and minimal damage to its molecular structure. The decolorization method developed in this study could be extended beyond PHU to treat polymeric materials that suffer from oxidation-induced coloration issues.