功能化二氧化碳基多元醇的精准合成

Precise Synthesis of Functional Carbon Dioxide-polyols

二氧化碳基多元醇(CO_(2)-polyol)是通过二氧化碳与环氧化物如环氧丙烷的调聚反应合成的一类端羟基功能化低聚物,然而具有后修饰特点的功能化CO_(2)-polyol的研究则少有报道.本文将衣康酸这一新型起始剂引入到环氧丙烷和CO_(2)的调聚反应中,成功地制备了双键功能化的CO_(2)-polyol.同时,衣康酸的生物来源属性进一步提高了生物碳比例,使得该多元醇的合成路线更为符合绿色可持续的理念.针对衣康酸存在酸性较强、双键较活泼等不利于PO/CO_(2)调聚反应的因素,采用具有多中心协同催化作用的铝卟啉低聚物催化剂,实现了含碳碳双键的CO_(2)-polyol的高效可控制备,且其链长和结构可调.所合成的具有活泼双键的不饱和多元醇为多种功能化二氧化碳基聚氨酯的合成提供了方便可行的操控平台.

CO_(2)-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 CO_(2)-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 CO_(2)to afford alkene functionalized CO_(2)-polyol.Parenthetically,the biorenewable 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 CO_(2)/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 byproduct.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 CO_(2)-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 oC).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 CO_(2)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 CO_(2)-polyols,this work may provide a viable synthetic toolbox,allowing the development of functional polyurethanes in nearly any direction.