Efficient and Scalable Synthesis of CO2-Based Polycarbonate Diols With Difunctional Initiator and Proton Exchange Agent

Abstract

CO₂-based polycarbonate diols (PPCDLs) are important raw materials. PPCDLs with high carbonate linkage (up to 99%) were controllably synthesized in high efficiency from CO₂ and propylene oxide (PO) by synchronously using tetrabutyl ammonium salt of succinic (ASA) as a difunctional initiator and 1,4-butanediol (BDO) as a difunctional proton exchange agent (PEA) in the presence of triethyl borane (TEB). In this system, the difunctional initiator (ASA) with two carboxylic anions accelerates the polymer chain propagation process, and the difunctional PEA with two active protons facilitates the proton exchange process. The molecular weight and production efficiency of PPCDL can be finely tailored by varying the feed molar ratios of PO to ASA, TEB, and BDO. Upon optimizing this scalable process, the PPCDLs with molecular weights between 1000 and 3000 Da are produced in high yields with a reaction time of 8–12 h, which is much faster than the monofunctional initiator in the presence of BDO (typically 20–36 h) or consumes much less amount of TEB and initiator in the absence of BDO. The synthesized PPCDLs possess a high 1^oOH content of the terminal hydroxyl groups and a high carbonate content. Thermoplastic poly(carbonate urethane)s (PCUs) are synthesized by copolymerization of the title PPCDLs, 4,4′-dicyclichexylmethane diisocyanate (HMDI) and BDO. Due to their high transparency and excellent mechanical properties, PCUs have great potential in the polyurethane industry, such as coatings, adhesives, leather, and thermoplastics.