Preparation of transparent CO₂ copolymer diol and its properties on waterborne polyurethane

CO₂ copolymer diol (PPCD) with superior transparency is an indispensable raw material for the polyurethane, especially for waterborne polyurethane coatings. However, commercial PPCD is generally opaque. In this work, A sustainable, colorless and transparent PPCD was prepared by using carbon dioxide (CO₂) and propylene oxide (PO) as raw materials. Research shows that the increase in CO₂ content (from 23.5 wt.% to 31.5 wt.%) will affect the transparency and thermal stability of PPCD and the transparency of PPCD with 29.1 wt.% CO₂ content is even higher than 90%, while the 5 wt.% mass loss temperature reaches 240.1 ℃. Furthermore, a series of waterborne polyurethane (WPU) was successfully synthesized by prepolymer method with PPCD as the soft segment. With the increase of CO₂ content, the thermodynamic property of WPU was significantly improved. When CO₂ content increased from 23.50 wt.% to 31.50 wt.%, the tensile strength increased from 23.27 MPa to 34.63 MPa and the elongation at break decreased from 750.85% to 520.37%, accompanied by the glass-transition temperature increased from -49.7 ℃ to -34.5 ℃. In addition, it was found that WPU prepared by transparent PPCD has better tensile strength, transparency, and storage stability. A new inspiration was provided for its application in the fields of optical components, transparent medical materials and UV curable coatings.