Preparation of novel CO 2 copolymer diol and its application on waterborne polyurethane

CO ₂ copolymer diol (PPCD) with superior transparency is an indispensable raw material for the polyurethane polymers, especially for water-based polyurethane coatings. However, commercial PPCD is generally opaque. In this work, A novel sustainable, colorless and transparent PPCD was prepared by using carbon dioxide (CO ₂ ) and propylene oxide (PO) as raw materials. Its basic structure was tested and verified by Fourier transform-infrared (FT-IR) and proton nuclear magnetic resonance ( ¹ H NMR) spectroscopy. Appropriate increase CO ₂ content did not obviously reduce the transparency and thermal stability of PPCD and the optimum value was 29.1 wt.%. Furthermore, the waterborne polyurethane (WPU) was successfully synthesized by prepolymer method with poly(1,4-butylene adipate) (PBA), polypropylene glycol (PPG) or prepared PPCD as the soft segment, respectively. With the increase of CO ₂ content, the thermodynamic property of WPU was significantly improved. When CO ₂ content increased from 23.50 wt.% to 31.50 wt.%, the tensile strength increased from 23.27 MPa to 64.63 MPa and the elongation at break decreased from 750.85–520.37%, accompanied by the glass-transition temperature increased from − 49.7 ℃ to -34.5 ℃. In addition, the WPU prepared by PPCD was also found to have better tensile strength, transparency and storage stability than that prepared by PBA and PPG. A new inspiration was provided to develop high-transparent CO ₂ based water-based polyurethane coatings.