Polyether polyol is an oligomer whose main chain contains ether bonds (-R-O-R-) and whose end or pendant groups contain more than two hydroxyl groups (-OH). It is formed by the ring-opening polymerization with oxidized olefin under the action of the catalyst using low molecular weight polyhydric alcohols, polyamines, or compounds containing reactive hydrogen as initiators.
Three kinds of raw materials are used to synthesize general polyether polyols: organic A oxide and furan cyclic compounds as the main body of polymerization reaction; initiators for adjusting the molecular weight and functional degree of polyether; catalysts that promote the polymerization reaction. The main raw materials are as follows:
1. The main body of polymerization reaction
Organic A oxides are mainly epoxypropane, ethylene oxide, epoxy chloropropane, and tetrahydrofuran. Under certain technological conditions, the carbon-oxygen chain can be broken, then the ring-opening polymerization reaction will happen, and the corresponding polyether polyol will be produced.
The second basic raw material synthesized with polyether is the initiator. At present, the initiators are basically divided into two types: low molecular compounds containing hydroxide radical and low molecular compounds containing amidogen or containing hydroxide radical and amidogen. The effects of using initiator are mainly in the following three aspects:
1) Control the molecular weight of the polyether polyol formed. If the amount of initiator is large, the molecular weight of polyether polyol synthesized is small; and the molecular weight of polyether polyol synthesized is large if the amount of initiator is small.
2) Polyether polyol with different functional degrees can be synthesized by the initiators containing the different numbers of active hydrogen atoms. The multifunctional polyether polyols used in polyurethanes are mostly realized by the use of a variety of low molecular compound initiators with different functionality degrees.
3) In addition to common alkyl alcohols, initiators containing other elements or structures can also be selected to give the synthetic polyether polyol with various special properties.
Catalysts are necessary for the smooth ring-opening of organic A oxides such as epoxypropane. There are many catalysts for the ring-opening reaction, and they can be divided into three types: anionic catalysts, cationic catalysts, and metal-complexed catalysts.