Double Metal Cyanide Catalyst Research Articles

Synthesis, Structure, and Actual Applications of Double Metal Cyanide Catalysts.

Double metal cyanide (DMC) complexes represent a unique family of materials with an open framework structure. The main current application of these complexes in chemical industry is their use as catalysts (DMCCs) of the ring-opening polymerization of propylene oxide (PO), yielding branched polyols, highly demanded in production of polyurethanes and surfactants. The actual problem of chemical fixing carbon dioxide from the atmosphere gave new impetus to the development of DMCCs, which turned out to be effective in oxirane/CO2 copolymerization. In recent years, new types and formulations of DMCCs were created, so that greater understanding of the reaction mechanisms was achieved and new fields of catalytic applications were found. In the present review, we summarized background and actual information about the synthesis, structure, and mechanisms of the action of DMCCs, as well as their application in the development of new materials and fine chemicals.

Preparation of Non-Isocyanate Polyurethanes from Mixed Cyclic-Carbonated Compounds: Soybean Oil and CO2-Based Poly(ether carbonate).

This study presents the synthesis and characterization of non-isocyanate polyurethanes (NIPU) derived from the copolymerization of cyclic-carbonated soybean oil (CSBO) and cyclic carbonate (CC)-terminated poly(ether carbonate) (RCC). Using a double-metal cyanide catalyst, poly(ether carbonate) polyol was first synthesized through the copolymerization of carbon dioxide and propylene oxide. The terminal hydroxyl group was then subjected to a substitution reaction with a five-membered CC group using glycerol-1,2-carbonate and oxalyl chloride, yielding RCC. Attempts to prepare NIPU solely using RCC and diamine were unsuccessful, possibly due to the low CC functionality and the aminolysis of RCC's linear carbonate repeating units. However, when combined with CSBO, solid NIPUs were successfully obtained, exhibiting good thermal stability along with enhanced mechanical properties compared to conventional CSBO-based NIPU formulations. Overall, this study underscores the potential of leveraging renewable resources and carbon capture technologies to develop sustainable NIPUs with tailored properties, thereby expanding their range of applications.

Multi-role heterogeneous Zn–Co double metal cyanide catalysts valid for ring-opening polymerizations and hydrofunctionalizations

Double metal cyanides (DMCs) or Prussian blue analogs are well-known solid complexes, especially because of their gas and energy storage ability and catalytic activity for epoxide polymerization. The crystal structure, as well as the electron-donating complexing agent, has a crucial effect on the catalytic activity and selectivity of these materials. In this study, we developed a feasible process for fabricating Zn–Co DMC catalysts, which have a range of crystal structures, using organosilicon complexing agents. In addition, the transformation of the complexing agent during catalyst preparation was investigated using density functional theory calculations to understand the nature of the active sites. The resultant catalysts exhibited excellent activities, good selectivities, as well as a broad substrate scope, for the homopolymerization of epoxide and lactone (turnover frequency up to 564 min−1), copolymerization of epoxide with CO2 (up to 99 % yield), and hydrofunctionalization reactions of terminal alkynes (up to 95 % yield), which are among the most important applications of DMC catalysis.

Synthesis of Polyether, Poly(Ether Carbonate) and Poly(Ether Ester) Polyols Using Double Metal Cyanide Catalysts Bearing Organophosphorus Complexing Agents.

We developed a series of Zn(II)-Co(III) double metal cyanide (DMC) catalysts with exceptional activity for the ring-opening polymerization of various cyclic monomers by employing diverse organophosphorus compounds as complexing agents (CAs). The chemical structure and composition of DMC catalysts were investigated by commonly used analysis such as infrared and X-ray photoelectron spectroscopies, and elemental analysis combining with in situ NMR analysis to determine the complexation types of organophosphorus compounds the catalyst framework. The resulting catalysts exhibited very high turnover frequencies (up to 631.4 min-1) in the ring-opening polymerization (ROP) of propylene oxide and good efficiency for the ROP of ε-caprolactone. The resultant polyester polyols are suitable to use as an macroinitiator to produce well-defined poly(ester ether) triblock copolymers of 1800-6600 g mol-1 and dispersity of 1.16-1.37. Additionally, the DMC catalysts bearing organophosphorus compounds CAs exhibited remarkable selectivity for the copolymerization of PO with CO2, yielding poly(ether carbonate) polyols with carbonate contents up to 34.5%. This study contributes to the development of efficient DMC catalytic systems that enable the synthesis of high-quality polyols for various applications.

Beta Zeolite-Supported Double-Metal Cyanide Catalysts with Enhanced Lewis Acidity for the Synthesis of High-Performance Poly(1,2-butylene oxide) Lubricating Oils

Beta Zeolite-Supported Double-Metal Cyanide Catalysts with Enhanced Lewis Acidity for the Synthesis of High-Performance Poly(1,2-butylene oxide) Lubricating Oils

Preparation of Well-Defined Double-Metal Cyanide Catalysts for Propylene Oxide Polymerization and CO2 Copolymerization.

Reevaluating the composition of the double metal cyanide catalyst (DMC) as a salt of (NC)6Co3- anions with 1:1 Zn2+/(X)Zn+ cations (X = Cl, RO, AcO), we prepared a series of well-defined DMCs, [ClZn+][Zn2+][(NC)6Co3-][ROH], [(RO)Zn+][Zn2+][(NC)6Co3-], [(AcO)Zn+][Zn2+][(NC)6Co3-], [(RO)Zn+]p[ClZn+](1-p)[Zn2+][(NC)6Co3-], [(AcO)Zn+]p[(tBuO)Zn+]q[Zn2+][(NC)6Co3-], and [(AcO)Zn+]p[(tBuO)Zn+]q[ClZn+]r[Zn2+][(NC)6Co3-]. The structure of [(MeOC3H6O)Zn+][Zn2+][(NC)6Co3-] was precisely determined at the atomic level through Rietveld refinement of the synchrotron X-ray powder diffraction data. By evaluating the catalyst's performance in both propylene oxide (PO) polymerization and PO/CO2 copolymerization, a correlation between structure and performance was established on various aspects including activity, dispersity, unsaturation level, and carbonate fraction in the resulting polyols. Ultimately, our study identified highly efficient catalysts that outperformed the state-of-the-art benchmark DMC not only in PO polymerization [DMC-(OAc/OtBu/Cl)(0.59/0.38/0.15)] but also in PO/CO2 copolymerization [DMC-(OAc/OtBu)(0.95/0.08)].

Cd(ii) and Zn(ii) coordination polymer-assisted CO2/cyclohexene oxide copolymerization with a double metal cyanide catalyst

Three new coordination polymers with Zn(ii) and Cd(ii) metal centers were synthesized and applied to cocatalyze CO2/CHO polymerization with DMC.

Analysis of propoxylation with zinc–cobalt double metal cyanide catalysts with different active surfaces and particle sizes

Propoxylation with DMCs involves external attack of ROH on a coordinated PO; the distance between the DMC particles determines the mass distribution.

(Co)polymerization Reactions with Participation of Cyclic Monomers Catalyzed by Double Metal Cyanide Catalysts

(Co)polymerization Reactions with Participation of Cyclic Monomers Catalyzed by Double Metal Cyanide Catalysts

Microstructural Insights into Ethylene Glycol‐Mediated Polyether Polyols Using Double Metal Cyanide Catalyst

AbstractPolyether polyols are well established category of polymers, which are synthesized via ring opening polymerization (ROP) industrially using Double Metal Cyanide (DMC) catalyst with glycols as initiators. Establishing the role of glycol in initiation and its involvement in the polymer chain during the ROP of propylene oxide (PO) via DMC catalysis is of utmost importance. In this work, the experimental method is established to understand the role of ethylene glycol (EG) and its participation during initiation and chain propagation. Furthermore, the microstructure analysis of synthesized polyether polyols reveals that ethylene glycol initiates from both sides and participated in random copolymerization besides its role as an initiator in the polymeric backbone during the ROP of PO. Also, in‐depth studies of the polymeric microstructural distribution are carried out using 1H‐1H COSY, 1H‐13C HMQC, and 1H‐13C HMBC with the aid of multi‐pulse 2D correlation techniques along with carbon‐13 NMR chemical shifts. In‐depth understanding of the microstructure of the polyether polyols is established with the aid of the obtained polymeric regio‐irregular structures. The reactivity ratios of PO are found to be 0.89 and 0.57 by modified Kelen–Tudos and Fineman–Ross method, respectively, indicating higher reactivity of PO monomer in comparison to EG.

Mechanistic insights into Schiff base incorporated double metal cyanide catalyst for the synthesis of colorless polyether polyols

The organic complexing agents (CAs) with multidentate sites help to enhance the active sites (Zn) of double metal cyanide (DMC) catalysts and also control the metal leaching from the DMC catalysts. Schiff base ligands (SBLs) are versatile and impart the coordination ability to bind with transition metals to form metal complexes. In this study, various SBLs are synthesized, and their use as CAs in DMC catalysts is thoroughly investigated. The metal complex formation is confirmed by structurally sensitive techniques, including SEM, PXRD, FT-IR, TGA, UV–Vis, AAS, CHNS, DLS, 1H-13C, XPS, and 13C-CP MAS spectroscopy. The 13C-CP MAS spectroscopy revealed strong coordination from N and O to the Zn sites of the DMC catalysts. XPS survey confirmed the presence of three types of cyanide (CN) carbons (axial, coordinated, and uncoordinated), four types of nitrogen (three from CN and one from azomethine), and Zn in +2 oxidation state. The ring-opening polymerization (ROP) was carried out using the prepared DMC catalysts to produce high-quality colorless polyether polyols (PPG). At an optimized reaction condition of catalyst amount = 250 ppm, time = 50 min, pressure = 5 bar, temperature = 105 °C, PO : PEG-600 = 4400 : 1, a maximum PPG yield (>95 %) is obtained with turnover frequency (TOF) of 11,292 h−1 (mol-PO per mol-Zn per hour). Density functional theory (DFT) calculations were also performed to understand the nature of the active site and mechanistic insight into the polymerization reaction.

Enhanced Double Metal Cyanide Catalysts for Modulating the Rheological Properties of Poly(propylene carbonate) Polyols by Modifying Carbonate Contents.

Poly(propylene carbonate) (PPC) polyol is an environmentally sustainable material derived from abundant and renewable greenhouse gas, CO2. Optimizing their synthesis and properties is crucial to their application in the production of polyurethane products. In this study, we synthesized PPC polyols with varying carbonate contents using heterogeneous Zn/Co double metal cyanide (DMC) catalysts, which were prepared with poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as an effective complexing agent. Analysis of the influence of calcination temperature revealed that the DMC-P123 catalyst calcined at 100 °C exhibited superior catalytic performance owing to reduced crystallinity and enhanced formation of the monoclinic phase. Additionally, by precisely controlling the CO2 pressure, high propylene carbonate contents of up to 32.8 wt % in the polyol structure were achieved. The increased carbonate content enhanced the intermolecular attraction between polyol chains, thereby promoting hydrogen bonding and significantly modulating the rheological properties of the polyol. The novel findings of this study establish a solid foundation for the synthesis of CO2-based polyols with desirable properties, serving as alternatives to conventional petroleum-based polyols.

Double Metal Cyanide (DMC) Catalysts: Synthesis, Structure, and Action Mechanism (A Review)

Double Metal Cyanide (DMC) Catalysts: Synthesis, Structure, and Action Mechanism (A Review)

Organic carbonates as green and sustainable complexing agents for double metal cyanide catalysts for the synthesis of polyether and poly(ether-carbonate) polyols

We investigated various linear carbonates, including dimethyl carbonate and diethyl carbonate, and cyclic carbonates such as ethylene carbonate, propylene carbonate (PC), butylene carbonate, and glycerol carbonate, as complexing agents (CAs) for the preparation of double metal cyanide (DMC) catalysts. The DMC catalysts bearing carbonate complexing agents exhibited good to excellent activities for the ring-opening polymerization of epoxides (turnover frequencies of up to 467 min−1) and the copolymerization of epoxides and CO2, producing polyether polyols with moderate molecular weights (1700–9700 g mol−1), narrow polydispersity indexes (1.1–1.2), very low unsaturation values (0.002–0.009), and low viscosities (438 −997 cP). The DMC catalyst bearing PC also afforded linear and branched polycarbonate polyols in high yields (up to 83%) and carbonate contents (up to 36 mol%). Density functional theory calculations were also performed to understand the effect of the CAs on the structural properties and activities of the corresponding DMC catalysts.

Sustainable Polycaprolactone Polyol-Based Thermoplastic Poly(ester ester) Elastomers Showing Superior Mechanical Properties and Biodegradability.

Thermoplastic elastomers (TPEs) have attracted increasing attention for a wide variety of industrial and biomedical applications owing to their unique properties compared to those of traditional rubbers. To develop high-performance engineering TPEs and reduce the environmental pollution caused by plastic waste, α,ω-hydroxyl-terminated polycaprolactone (PCL) polyols with molecular weights of 1000-4200 g mol-1 and polydispersity index (Ð) of 1.30-1.88 are synthesized via the ring-opening polymerization of sustainable ε-caprolactone using a heterogeneous double metal cyanide catalyst. The resulting PCL polyols are employed as soft segments to produce thermoplastic poly(ester ester) elastomers and are compared to conventional thermoplastic poly(ether ester) elastomers prepared from polytetramethylene ether glycol (PTMEG). Notably, the PCL-based TPEs exhibit superior mechanical properties and biodegradability compared to PTMEG-based TPEs owing to their crystallinity and microphase separation behaviors. Accordingly, they have 39.7 MPa ultimate strength and 47.6% biodegradability, which are much higher than those of PTMEG-based TPEs (23.4 MPa ultimate strength and 24.3% biodegradability). The introduction of biodegradable PCLs demonstrates significant potential for producing biodegradable TPEs with better properties than polyether-derived elastomers.

Prussian blue analogs as catalysts for the fixation of CO2 to glycidol to produce glycerol carbonate and multibranched polycarbonate polyols

A series of Prussian blue analogs (PBAs) having a range of crystal structures and compositions was investigated as heterogeneous catalysts for the fixation of carbon dioxide (CO2) to glycidol. The morphology of PBAs was modified, as confirmed by structural characterization, by varying the precipitation method. Of the prepared catalysts, the cubic Zn(II)-Co(III) PBA exhibited the highest catalytic activity (turn-over frequency up to 763 h−1), selectivity (up to 94%), and recyclability for the cycloaddition of CO2 to glycidol. In addition, branched polycarbonate polyols having tunable branching degree (0.15–0.61) and linear polycarbonates of relatively high carbonate content (up to 64.2%) were produced via ring-opening (multibranching) copolymerization of CO2 and various epoxides using a highly amorphous Zn(II)-Co(III) double metal cyanide catalyst. Mechanistic pathways have been proposed by combining experimental results with computational studies.

In situ Monitoring of Double Metal Cyanide (DMC) Catalyst Synthesis by Raman Spectroscopy

Double metal cyanide (DMC) catalyst is widely used for the alkoxylation reaction to produce polyether polyol from ethylene/propylene/butylene oxides. It is challenging to optimize the synthesis process, due to the lack of real-time understanding of the speciation of the reaction mixture. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and actual alkoxylation reaction performance are effective ways for the evaluation of success of each synthesis, but it is difficult to guide process optimization. An in situ Raman method is developed in this study to monitor the DMC catalyst synthesis in real time to accelerate the process optimization. The synthesis involves the reaction of ZnCl2 and K3Co(CN)6 (KHCC) to form Zn3[Co(CN)6]2 (ZHCC). ZHCC is then converted to DMC in the presence of excess of t-butanol and ZnCl2 in the second step. Characteristic KHCC Raman peaks were observed at 2138 and 2153 cm-1, ZHCC at 2185 and 2206 cm-1, and DMC at 2203 and 2225 cm-1, respectively. This enables realtime tracking of both steps’ conversion. Both t-butanol and ZnCl2 concentrations were found to substantially influence the kinetics of DMC formation, but not the Raman spectra of the final DMC products. The reaction time could be adjusted from hours to minutes through the control of reactant concentrations.

Organonitriles as complexing agents for the double metal cyanide-catalyzed synthesis of polyether, polyester, and polycarbonate polyols

A series of double metal cyanide (DMC) catalysts prepared using nitrile compounds as complexing agents (CAs) was employed for the synthesis of polyether, polyester, and polycarbonate polyols. The DMC catalysts bearing nitrile CAs exhibited remarkably higher activities toward the ring-opening polymerization (ROP) of propylene oxide (PO) and ε-caprolactone (CL), as well as toward the copolymerization of PO with CO2, than conventional DMC catalysts prepared using tert-butyl alcohol as a CA. Accordingly, DMC catalysts bearing 2-methylbutyronitrile or isobutyronitrile showed the highest activities for the ROP of PO (TOF=533 min−1) and CL (TOF=83 h−1), respectively, whereas the DMC using acetonitrile CA exhibited the highest efficiency for the copolymerization of PO and CO2 (TOF=475 h−1). The resultant polypropylene oxide polyols were characterized by a narrow polydispersity index (1.1 −1.2) and a low unsaturation level (0.004−0.014). In addition, the DMC catalyst bearing isobutyronitrile afforded α,ω-hydroxyl-terminated polycaprolactones with controlled molecular weights (1000−9800 g mol−1) and a narrow polydispersity index of 1.1−1.5. Polycarbonate polyols with relatively high yields (56–67 %) and carbonate contents (30–38 %) were also obtained.

Oligomeric Heterogeneous Double Metal Cyanide Catalyst for One‐pot Ring‐Opening Polymerization

AbstractA series of efficient oligomeric zinc and cobalt‐based double metal cyanide (DMC) catalysts was prepared using Ethylenediaminetetracetic acid (EDTA) as an organic complexing agent (CA) and tested for ring‐opening polymerization (ROP) of propylene oxide (PO) to synthesize polyether polyols (PPG). The complex formation of EDTA with Zn and cyanide (CN−) with Zn surface and morphology of the DMC catalyst were confirmed by PXRD, FTIR, SEM, and UV‐Vis. Furthermore, the13C‐CP MAS spectroscopy showed an integral ratio of 3.2 : 1 for the bound and free carboxyl group of EDTA in the catalyst, respectively. The maximum yield (>98 %) of PPG with turnover frequency (TOF) of 9625 h−1was obtained with controlled PDI (1.1) in only 1 h with 1330 g mol−1Mw, 0.009 meq g−1unsaturation number, and 8.1 mg‐KOH g−1OH value at optimized reaction condition (Catalyst amount=0.015 g, Time=1 h, Temperature=105 °C, Pressure=5 bar, PO : PEG‐600=40 : 1). The ROP showed first‐order kinetics behavior by1H NMR spectroscopy with proposed coordination mechanism.

EDTA incorporated Fe-Zn double metal cyanide catalyst for the controlled synthesis of polyoxypropylene glycol

EDTA incorporated Fe-Zn double metal cyanide catalyst for the controlled synthesis of polyoxypropylene glycol