Metal-Free Synthesis of Biodegradable CO2-Based Oligo(carbonate-ester) Diols as Building Blocks for Thermoplastic Polyurethanes

We for the first time synthesize a type of biodegradable CO2-based oligo(carbonate-ester) diol (PPCPDL) with aromatic ester units via a one-pot immortal copolymerization using carbon dioxide (CO2)/propylene oxide (PO)/phthalic anhydride (PA) as raw materials and 1, 4-butanediol (BDO) as proton exchange agent (PEA), respectively, catalyzed by metal-free triethylborane/triethylamine (TEB/TEA) Lewis pairs. A series of PPCPDLs with molar mass (Mn) ranging from 1100 to 7100 Da and polyester content (PE mol %) between 0 and 36% were constructed by tuning the reaction temperature, CO2 pressure, reaction time, and feeding ratio. Our strategy adopts PA as a third monomer to incorporate aromatic PE blocks into the PPCPDLs, affording the resulting thermoplastic polyurethanes (TPUs) with improved thermal/mechanical properties. TPU-PPCPDL with aliphatic carbonate- and aromatic polyester-units can deliver the highest tensile strength of 35.2 MPa and hardness of 97 (Shore A), superior to the commercial diols-based TPUs. Twenty wt % of propylene glycol (PPG) was also introduced as the second soft segment into the TPU-PPCPDLs to endow the obtained TPUs with various physical properties, including good thermal stability, light transmittance, and mechanical behaviors, which indirectly highlights the application value and significance of such PPCPDLs as building blocks in TPU production.