The Effect of Oligo-Polyol Functionality

This behaviour concerning the cumulative effect of functionality and molecular weight of oligo-polyols is observed in the case of PU foams (flexible, semiflexible and rigid) based on stress-strain relationship [2, 12]. 

These good recovery properties are the reason why the preferred term is semiflexible foams and not semirigid foams. 

Dimensional stability of rigid PU foams (a very important characteristic in the thermoinsulation of refrigerators, especially at lower temperatures) is strongly improved by using high functionality oligo-polyols. 

Fortunately, after the gel point, the reaction between unreacted -NCO groups and unreacted OH groups continues slowly, over time, and the properties are improved, especially when very high functionality oligo-polyols are used which is when the best dimensional stabilities are obtained. 

A very subtle effect of the oligo-polyols functionality is seen in the case of propoxylated polyether polyols, due to the presence in oligo-polyol composition of a polyether monol as a consequence of the rearrangement of PO to allyl alcohol during anionic PO polymerisation (see section 4.1), with this structure  

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