Polyhydroxyurethanes (PHUs) Derived from Diphenolic Acid and Carbon Dioxide and Their Application in Solvent- and Water-Borne PHU Coatings

To develop biobased polyurethanes (PUs) via a less hazardous, nonisocyanate route, herein we synthesize a series of biobased polyhydroxyurethanes (PHUs) by reacting a new biobased cyclocarbonate (derived from renewable diphenolic acid and carbon dioxide) with ethylenediamine (EDA), diethylenetriamine (DETA), and isophoronediamine (IPDA), corresponding to PHU-EDA, PHU-DETA, and PHU-IPDA, respectively. Their molecular structures are identified from 1 H NMR and FTIR analyses. Gel permeation chromatography (GPC) analysis shows that the molecular weights of these PHUs grow to as high as 5 kDa in a short reaction time (4 h) at a relatively low reaction temperature (80 °C). Subsequently, the solvent-borne (in acetone) coatings of these PHUs are successfully fabricated with diglycidyl ether of bisphenol A as the cross-linker. The cured PHU coatings on aluminum panels show the high pencil hardness (up to 4 H), adhesive force (up to grade 1), glass transition as high as 116 °C, and initial thermal degradation temperature up to 190 °C. Furthermore, we realize the good dispersion of these PHUs in water by introducing chemically bonded carboxylic anions into the molecular backbone to form a stable aqueous emulsion with well-controlled particle sizes and further demonstrate its application in a water-borne PHU coating with good mechanical and thermal properties. Overall, we develop a facile yet effective method to prepare sustainable, biobased PHUs based on diphenolic acid and carbon dioxide via a safer, greener nonisocyanate route and furthermore demonstrated their use as solvent-borne coatings and greener water-borne coatings of reduced environmental impact.