Sequential DMC/FAB-Catalyzed Alkoxylation toward High Primary Hydroxyl, High Molecular Weight Polyether Polyols

A catalytic alkoxylation process to make higher molecular weight poly(propylene oxide) and poly(propylene oxide-co-butylene oxide) polyols containing greater than 65% of primary hydroxyl end groups is described. The one-pot method employs the double metal cyanide catalyst and tris(pentafluorophenyl)borane catalyst (FAB) in a sequential manner and exploits the high primary hydroxyl regioselectivity of FAB over a broad range of temperatures. The process was carried out in two sequential steps: (a) DMC-catalyzed epoxide ring-opening polymerization at a temperature of >130 degrees C and (b) FAB-catalyzed regioselective capping at a temperature between 60 and 110 degrees C. The approach thus combines the relative advantages of both the DMC and FAB catalysts: high activity and high primary hydroxyl regioselectivity, respectively. It is also demonstrated that sufficiently low levels of FAB catalyst (e.g., 150 ppm) are sufficient, thus obviating the need for catalyst removal from the final product.