The initiator, type of olefin oxide and molecular weight mainly determine the physicochemical properties of polyether polyols:
1. The amount of reactive hydrogen of the initiator determines the functionality of the polyether. The reactivity of polyethers synthesized by different starting agents varies greatly. In general, when the molecular weight difference is not large, polyether and ethylenediamine. The polyethers with aniline as the initiator have the highest activity and pentaerythritol. The polyether activity of sucrose polyol as a starting agent is also relatively high. The polyether activity of ethylene glycol and propylene glycol as the starting agent is relatively low.
2. For the same type of polyether, the higher the hydroxyl value and the smaller the molecular weight, the higher the reactivity and the smaller the viscosity.
3. Most polyethers of oxo-olefins are synthesized by PO, or all are synthesized by PO, but there are some varieties, first with PO and the initiator reaction, and then capped with EO, and some varieties are even polymerized with EO. polyethers with EO sealed ends usually have higher activity and hydrophilicity than those with all PO. the higher the EO content, the more obvious this trend.
Based on the reactivity from low to high, we can simply distinguish between polyethers:
Poly Propylene Glycol Oxide, PPG
Functionality 2 or 3, initiator 1, 2-propanediol, ethylene glycol, trimethylolpropane or glycerol, polymerization for PO ring opening. Most of the polyethers on the market for soft foam polyethers and adhesive elastomers are of this type, and are our most common general purpose polyethers, generally numbered 210, 220, 330. the first number represents the functional degree, and the last two numbers represent the molecular weight. Polyether 210 is a polyoxy propylene glycol with a functional degree of 2 and a molecular weight of 1000.
The structure is similar to ordinary polyether, but some PO chain segments are changed to EO sealed ends. The difference in molecular structure leads to increased activity. the higher the EO content, the higher the activity and the higher the hydrophilicity. The common high reactive polyether is 330N.550N.
1. Polyethers are synthesized with ethylenediamine and aniline as starting agents, the most common ones are polyether 403 and 4110, which are commonly used in hard foam. This kind of polyether has certain autocatalytic effect because of the amino group, it is rarely used alone, but usually used in combination with the above two polyethers.
2. Polyfunctional polyether with sorbitol as the starting agent, the reactivity is also very high, basically only used for hard foam.
Distinguishing polyethers from the perspective of reactivity can better enable us to understand the formulation from the molecular point of view, helping us to improve the efficiency of the experiment and avoid detours. Most of the time, we design formulations that rarely use only one polyether, and most of them are used to balance properties. The closer the difference in reaction activity gradients, the stronger the cure and the more performance can be demonstrated at later maturity. However, the curing gradient varies widely, so it is necessary to consider multiple catalysis. The greater the difference, the more likely it is that incomplete curing will result, leading to formulation design failure.
For example, in many cases, several polyethers are mixed and cured into white cloudy or tofu lumps. The reason for this is that the highly reactive polyether cures first and the three-dimensional structure formed prevents the less reactive polyether from continuing to cure, leading to incomplete reactions and inconsistent curing.
