Intermediate propoxylated polyethe

When EO reacts with the intermediate propoxylated polyether having secondary hydroxyl terminal groups, two competitive reactions take place ... 

An important aspect of the ethoxylation reaction is that the primary hydroxyl content depends strongly on the hydroxyl number of the intermediate propoxylated polyether polyol. If a polyol is ethoxylated, an intermediate propoxylated polyether with an high hydroxyl number is obtained if the ethoxylation is done with a lower primary hydroxyl content with the same quantity of EO, an intermediate propoxylated polyether with a lower hydroxyl number is obtained (see Table 4.9). 

Table 4.9 The effect of the hydroxyl number of the intermediate propoxylated polyether polyol on the primary hydroxyl content (EO concentration was around 10% against final polyol) [50] ...

In conclusion, in order to obtain high percentage primary hydroxyls, it is necessary to remove very efficiently the remaining PO after the synthesis of the intermediate propoxylated polyether. 

Equation 4.20 shows that mass transfer is a determining factor in anionic polymerisation of PO, a high surface area of the liquid reaction mass giving high rates of PO consumption. On the other hand, due to the very high efficiency of stirring, the gas-liquid contactor reactor type assures a very narrow MW distribution of the resulting polyether. For the ethoxylation of intermediate propoxylated polyethers (in block copolymers PO-EO... 

Excellent PO-EO block copolyether polyols with terminal poly[EO] block, are formed by the addition, to the intermediate propoxylated polyether obtained with DMC catalysts, of an anionic catalyst (KOH or potassium alcoholates) followed by the addition of EO by classical technology, via an anionic mechanism. By this relatively complicated route, it is possible to obtain PO-EO block copolymers with high primary hydroxyl content and very low unsaturation. 

The polyether diols, block copolymers of PO-EO with terminal poly[EO] block are obtained absolutely identically to the previously described EO capped polyether triols, the difference being that the propoxylated intermediate is a propoxylated polyether diol. 

The synthesis of polyether triols, block copolymers with terminal poly[EO] block is relatively simple in the first step a propoxylated intermediate polyether is synthesised by the polyaddition of PO to the starter (glycerol or propylene glycol). After the addition of the required quantity of PO, the unreacted monomer is eliminated by vacuum distillation and the polymerisation continues by the addition of EO, the second monomer. 

Figure 4.26 Variation of the reactivity constant r1 versus temperature in ethoxylation of the propoxylated intermediate polyethers...

The advantage of these types of processes direct propoxylation of a mixture of high melting point polyol with a low melting point polyol, is the perfect control of the final functionality in the resulting polyether (function of the ratio of sucrose/second polyol), and the simplicity of the process with only one propoxylation step, without intermediate distillations. 

Polyether polyols for rigid PU foams or intermediate polyether polyols (with a higher hydroxyl number than the final polyether) proved to be excellent reaction media for the propoxylation of solid polyols, especially to obtain very high functionality polyols. These polyether polyols, used as a liquid reaction medium, are called heel . For example, at the PO polymerisation temperature (110-120 °C) a mixture of 60% sucrose and 40% sucrose-based polyether polyol is a perfectly stirrable mixture. 

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