Unsaturation polyether triols

Figure 5.2 The polyether triol unsaturation obtained with DMC catalysts, compared with that obtained with potassium hydroxide...

The polyether triol functionality as function of unsaturation and of diol content can be calculated using the following formula ... 

Figure 4.11 The effect of some ligands of potassium cation on the unsaturation of the polyether triols. Temperature 110 °C Pressure 0.4 MPa catalyst concentration 0.0056 mol/1 Ligands polyethylene glycol MW = 2000 ( ) and 18-crown 6 (())...

As an initial level, at a polymerisation temperature range of 110-120 °C, the excess of PO needed is around 10-15% for a MW of 3000-3600 daltons, 20-30% for a MW of 4700-5000 daltons and 35-50% for a MW of 6000-6500 daltons. To obtain low unsaturation in conditions of convenient reaction rates, one considers that 105-110 °C is an optimum polymerisation temperature. Sometimes, for high MW polyethers (MW = 6000-6500 daltons), the final quantity of PO (around 35-40% from the total quantity of PO needed) is added at lower polymerisation temperatures of 90-105 °C or even 90-95 °C. It is a sacrifice for the polymerisation rate but results in an increase in the quality of the synthesised polyether, which will have a low unsaturation, corresponding to a low quantity of polyether monol in a polyether triol. 

DMC catalysts are considered to be the ones that perform best at this time for PO polymerisation initiated by hydroxyl groups. Bayer developed the first continuous process, with a very high productivity, for the synthesis of polyether polyols with DMC catalysts (IMPACT Catalyst Technology). In a short and simple production cycle, a large variety of polyether diols of very low unsaturation for elastomers, sealants, coatings and low monol content polyether triols destined for flexible polyurethane foams are obtained. This is one of the best developments in the last few years in the field of polyether polyol synthesis [2],... 

Reaction 11.4 is used to decrease the unsaturation of polyether polyols simultaneously with the functionality increase. Thus, by introducing a polyether polyol with high unsaturation (0.07-0.09 mequiv/g), a low molecular weight polysiloxane compound, having 2-3 Si-H groups/mol, together with a platinum catalyst, the polyether monol present in the polyether (in fact allyl ether based polyethers) is added to the polysiloxane compound and the monol is transformed into a diol or into a triol (reaction 11.5). 

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