Double metal cyanide catalysts bearing lactate esters as eco-friendly complexing agents for the synthesis of highly pure polyols

Abstract

A green way of synthesizing double metal cyanide (DMC) catalysts for the ring opening polymerization of propylene oxide has been developed by using environmentally friendly and nontoxic lactate esters as complexing agents (CAs). The total amount of CA consumed in the catalyst preparation procedure can also be greatly reduced by combining with co-complexing agents bearing polyether backbones. The DMC catalysts produce highly pure polymers in high activity, enough to avoid labor, energy, and time-consuming catalyst removal procedures.

Structural properties and chemical bonds in double metal cyanide catalysts

“…EDX analysis provides the Zn/O ratio 1.6, 0.85 and 0.34 as characteristic for bulk materials, thus indicating that in the bulk of the MEO‐DMC 2, much more ligands are accumulated than in MEO‐DMC 1. The type and amount of oxygen atoms coordinated Zn may play an important role in the catalytic properties as was suggested in Yoon et al . The ratio of Co/O follows the same tendency.…”

“…This means that the complexion of organic ligand makes the basic crystalline Zn 3 [Co(CN) 6 ] 2 unit substantially amorphous. The crystallinity of the catalyst may strongly influence the catalytic activity as is discussed in the literature (see e.g . and references therein).…”

“…Some interesting promises seem to arise from the XPS studies results. For example, a few eV shift of the binding energy of Zn was reported by several researchers as a result of probable oxygen atom coordination, but this proposition should be verified by analogous XPS examination of ‘pure’ non‐catalytic hydrated trizinc bishexacyanocobaltate(III) compound (Zn 3 [Co(CN) 6 ] 2 ), considering possible Zn–OH 2 coordination bonds formation.…”

“…However, the aforementioned techniques are usually used to confirm the identity of the obtained material. Results of the application of XRD have been described in the works of Kim and colleagues . XRD method allowed to follow changes in the crystal structure of DMC catalysts during the different processes used for catalyst preparation and to look for a relationship between the formation of different phases and catalyst activity .…”

“…No unambiguous spectral effects, characteristic for catalytically active Zn atoms centers, have been differentiated using infrared spectrophotometric studies of DMC catalysts. Although some characteristic absorption ranges have been found, corresponding to the specific valence vibrations ν (C ≡ N), ν (Co‐C), and some subtle frequency shifts connected mainly with the crystalline phase properties have been noticed, not any explicit evidences for the presence of catalytic centers have been found …”