Precise Synthesis of Functional Carbon Dioxide-polyols

CO2-polyols, comprised of both rigid carbonate and soft ether, contribute to important raw material innovation in the polyurethane industry, however, only rare examples have demonstrated functional CO2-polyols for the purpose of post-modification. In this work, itaconic acid as a novel starter was introduced in the telomerization of propylene oxide and CO2 to afford alkene functionalized CO2-polyol. Parenthetically, the bio-renewable nature of itaconic acid also raised the bio-based carbon ratio in the structure of polyol, which further elevated the sustainability impact of the whole synthetic process. The major challenge of the preparation arose from the compatibility between itaconic acid and the involved CO2/epoxide copolymerization catalyst. The first is that the strong acidity of itaconic acid may retard the catalysis and form certain amount of cyclic carbonate as by-product. The second is to retain the active double bond requires rather low reaction temperature which also decreases the activity. Nevertheless, we adopted a highly active Al(III) porphyrin oligomer catalyst to prepare itaconic acid based CO2-polyol. Its multisite cooperative catalysis helped to overcome such obstacles, mediating the telomerization in both effective and well-controlled manner. Turnover frequency values of 2080-2500 h(-1) were achieved even in the prerequisite of the full conversion and low temperature (60 degrees C). The selectivity was also remarkable as the amount of cyclic carbonate was controlled around 1 wt% in all cases. Meanwhile, the afforded polyols had tunable chain length of 1900-3800 g/mol and carbonate fraction of 15.9%-54.3%, which can be customized by adjusting the itaconic acid feed and CO2 pressure. Finally, a proof-of-concept study disclosed the activity of double bond which remained intact in the derived polyurethane. Hence, by the introduction of such unsaturated CO2-polyols, this work may provide a viable synthetic toolbox, allowing the development of functional polyurethanes in nearly any direction.