Preparation of double-metal cyanide catalysts with H3Co(CN)6 for propylene oxide homo- and CO2-copolymerization

A preparative-scale (100 g scale) synthesis of H3Co(CN)(6) was achieved, the structure of which was unambiguously determined using X-ray crystallography. Double-metal cyanide complexes (DMCs) were facilely prepared with the prepared H3Co(CN)(6); mixing H3Co(CN)(6) and Zn(EH)(2) (EH = 2-ethylhexanoate) in methanol precipitated solids, which were used for polymerization after solvent removal. The prepared DMCs exhibited good activity in PO homopolymerization even in the presence of a propylene glycol (PG) starter. A conventional DMC prepared by the salt metathesis reaction of K3Co(CN)(6 )with ZnCl2 in water was inactive in the presence of such a simple PG starter. The prepared DMC was also active in PO/CO2 copolymerization, although its productivity was substantially lower under CO2 pressure. The carbonate linkage fraction was high (FCO2 = 0.48-0.66, depending on the CO2 pressure), although the generation of a small amount of cyclic carbonate was inevitable (similar to 10 wt%). However, feeding a starter, such as polypropylene glycol (PPG) or adipic acid, to obtain low-molecular-weight macrodiol deteriorated the catalytic performance. A substantial amount of cyclic carbonate was concomitantly generated (similar to 30 wt%).