Catalytic Ring-Opening Polymerization of Propylene Oxide by Organoborane and Aluminum Lewis Acids

Catalytic ring-opening polymerization of propylene oxide (PO) was studied with 12
organoborane and aluminum catalysts in combination with 12 hydroxylic initiators. These catalysts vary
in Lewis acidity and ligand steric bulk, whereas the initiators differ in their functional groups and Brønsted
acidity. This study examined four aspects of PO polymerization:  degree of polymerization control, effects
of catalyst and initiator structure on activity and polymer molecular weight, reactions of catalyst with
initiator and catalyst with monomer, and structures of PPOs produced. In the absence of hydroxylic
initiators, B(C6F5)3 predominantly catalyzes isomerization of PO to propionaldehyde in hexanes and
additionally produces low oligomers in toluene; interestingly, the sterically encumbered perfluorobiphenyl
borane B(C12F9)3 affords no such isomerization products. With addition of sufficient high concentration
of hydroxylic initiators in a [PO]0:[−OH]0 ratio of 41.7, however, PPOs with the desired Mn range of a
few thousand dalton and low PDI of

本研究探讨了以氧化丙烯（PO）为原料，结合12种有机硼烷和铝催化剂，并与12种羟基引发剂共同进行的催化开环聚合反应。这些催化剂在路易斯酸性和配体立体体积上存在差异，而引发剂则在官能团和布朗斯台德酸性方面有所区别。本项研究深入探讨了PO聚合的四个方面：聚合度控制、催化剂和引发剂结构对活性和聚合物分子量的影响、催化剂与引发剂以及催化剂与单体之间的反应，以及所生成的PPOs的结构。在没有羟基引发剂的情况下，B(C6F5)3主要催化PO在己烷中的异构化反应生成丙醛，并在甲苯中产生低聚物；有趣的是，具有空间位阻的过氟双苯硼烷B(C12F9)3并未产生此类异构化产物。然而，在加入足够高浓度的羟基引发剂，且[PO]0:[−OH]0的摩尔比为41.7时，却能够得到所需分子量范围在数千道尔顿左右且PDI较低的PPOs。