Ring-Opening Polymerizations of Propylene Oxide by Double Metal Cyanide Catalysts Prepared with ZnX 2 (X ¼ F, Cl, Br, or I) IL KIM, SEUNG HOON BYUN, CHANG-SIK HA Department of Polymer Science and Engineering, Pusan National University, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Korea Received 11 January 2005; accepted 1 May 2005 DOI: 10.1002/pola.20914 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Polymerizations of propylene oxide were carried out with double metal cyanide (DMC) catalysts based on Zn 3 [Co(CN) 6 ] 2 . Through the control of the type and amount of ZnX 2 (X ¼ F, Cl, Br, or I) during the preparation of the catalyst, the cata- lytic activity, induction period, and unsaturation level in the polyether polyols could be tuned. The DMC catalysts were characterized by X-ray photoelectron spectroscopy, infrared spectroscopy, and X-ray powder diffraction. In general, ZnBr 2 was the most effective zinc halide with respect to the properties of the resulting polymers as well as the activity and induction period. The average rates of polymerizations of DMC catalysts prepared with ZnCl 2 , ZnBr 2 , and ZnI 2 were 889, 1667, and 784 g of polyoxy- propylene/g of catalyst h, respectively, with induction periods of about 53, 5, and 60 min, respectively, at 115 8C. The DMC catalysts produced polyoxypropylenes with an ultralow unsaturation level (0.0025–0.0057 mequiv/g) and a narrow molecular weight distribution (1.07–1.42) without high-molecular-weight tails; this resulted in a low viscosity (962–3950 cP). According to the results collected from catalyst charac- terizations and polymerizations, the active sites of DMC-catalyzed polymerization had mainly coordinative characters. The presence of free anions accelerated the ring- opening procedure and thus enhanced the propagation rate and shortened the induc- tion period. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4393–4404, 2005 Keywords: catalysts; double metal cyanide; polyols; propylene oxide; ring-opening polymerization; transition metals; zinc halides INTRODUCTION Double metal cyanide (DMC) compounds are well-known catalysts for epoxide polymerization, that is, for polymerizing alkylene oxides such as propylene oxide (PO) and ethylene oxide to yield poly(alkylene oxide) polymers, which are also called polyether polyols. 1,2 In conventional base- catalyzed oxyalkylation reactions, PO and cer- tain other alkylene oxides are subject to a com- peting internal rearrangement that generates unsaturated alcohols. The resulting product will contain allyl alcohol initiated, monofunctional impurities. As the molecular weight of the polyol increases, the isomerization reaction becomes more prevalent. The monofunctional impurities tend to reduce the average functionality and broaden the polydispersity of the polyol. Unlike base catalysts such as KOH and CsOH, DMC catalysts do not significantly pro- mote the isomerization of PO. As a result, DMC catalysts can be used to prepare polyols that have low unsaturation values and relatively high molecular weights. DMC catalysts can be Correspondence to: I. Kim (E-mail: ilkim@pusan.ac.kr) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, 4393–4404 (2005) V V C 2005 Wiley Periodicals, Inc. 4393