Tuning of the Activity and Induction Period of the Polymerization of Propylene Oxide Catalyzed by Double Metal Cyanide Complexes Bearing β-Alkoxy Alcohols as Complexing Agents

For the development of commercially viable catalyst systems for the polymerization of propylene oxide (PO), a series of double metal cyanide (DMC) complexes have been developed by reacting aqueous zinc(II) chloride with aqueous potassium hexacyanocobaltate(III) in the presence of various complexing agents (CAs) such as 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-butoxyethanol (BE), 1-methoxypropan-2-ol, 1-ethoxypropan-2-ol, 1-propoxypropan-2-ol, and 1-butoxypropan-2-ol (BP) with different polarities and tert-butyl alcohol ((BuOH)-Bu-t). The catalyst composition was estimated by combining elemental analysis with thermogravimertic analysis. The coordination of the CA can be identified by employing X-ray photoelectron spectroscopy, X-ray diffraction patterns, and infrared spectroscopy of the catalysts. Pursuing a catalyst system showing favorable polymerization behavior for commercial aspects of both catalytic activity and reaction control, the kinetics of PO polymerizations were investigated by using 4 and 8 L reactors equipped with pilot programmable logic controller systems. While a DMC catalyst bearing (BuOH)-Bu-t as a CA showed a long induction period, it gave a very high overall rate of polymerization once activated, resulting in severe exothermic reactions that are hard to control. This problem could be successfully overcome by using the DMC catalysts bearing BE or BP as a CA. All polyether polyols were analyzed by measuring their unsaturation level, molecular weight, and distribution. All of the polyols produced featured a low level of unsaturation (0.014-0.024 mequiv g(-1)), moderate number-average molecular weights (900-3400), and very narrow polydispersities (1.04-1.19).