The physical and chemical properties of polyether polyols are mainly determined by the types and molecular weights of initiators and oxidized olefins:
1. The amount of active hydrogen in the initiator determines the performance of polyether. The reactivity of polyether synthesized by different initiators is quite different. In general, polyether and ethylenediamine can be used when the molecular weight difference is small. Polyether with aniline as initiator has high activity and is pentaerythritol. The activity of polyether with sucrose polyol as initiator is higher, while that with ethylene glycol as initiator is higher. Polyether with propylene glycol as initiator has low activity.
2. For polyethers of the same type, the higher the hydroxyl value, the smaller the molecular weight, the higher the reactivity and the lower the viscosity.
3. Most oxidized olefin polyethers are synthesized by PO or with PO, but some varieties react with PO and initiator first, and then with EO, and some varieties even polymerize with EO. EO terminated polyethers generally have higher activity and hydrophilicity than all PO polyethers. The higher the EO content is, the more obvious this trend is.
According to the reaction activity from low to high, we can simply distinguish polyethers:
Low activity polyether
Epoxy polypropylene, PPG
The function is 2 or 3, the initiator is 1,2-propanediol, ethylene glycol, trimethylpropane or glycerin, and polymerization is used for PO ring opening. Polyethers used in soft foam polyethers and adhesive elastomers on the market mostly belong to this type. They are also common general-purpose polyethers, usually numbered 210, 220 and 330. The last two numbers represent the molecular weight. Polyether 210 is a polyoxypropylene glycol, with a functionality of 2 and a molecular weight of 1000.
Medium active polyether
The structure is similar to that of ordinary polyether, but some PO chain segments are changed to EO sealed ends. The difference of molecular structure leads to the increase of activity. The higher the EO content, the higher the activity and the stronger the hydrophilicity. The common high resilience polyether is 330N.550N.
Highly reactive polyether
1. Polyether was synthesized with ethylenediamine and aniline as initiators. The common ones are polyethers 403 and 4110, which are usually used for hard foam. This kind of polyether has a certain autocatalytic effect because it contains amino groups. It is rarely used alone and is usually used in combination with the above two polyethers.
2. Multifunctional polyether and sorbitol also have high activity as initiators, and are basically only used for rigid foam.
Distinguishing polyethers from the perspective of reactivity can better enable us to understand the molecular formula from the perspective of molecules, help us improve experimental efficiency and avoid detours. Most of the time, we rarely use only one kind of polyether in the design formula, and most polyethers are used for balancing performance. The closer the gradient difference of reaction activity is, the stronger the curing effect will be, and the stronger the performance will be when it matures later. However, the curing gradient varies greatly, so it is necessary to consider multiple catalysis. The greater the difference, the more likely it is to lead to incomplete curing, leading to formula design failure.
For example, in many cases, several polyethers are mixed and solidified into a white haze or tofu block. The reason is that the polyether with high reactivity is cured first, and the three-dimensional structure formed prevents the polyether with low reactivity from continuing to cure, resulting in incomplete reaction and inconsistent curing.
