Oligo-polyols characteristics

Irrespective of the chemical structure of the oligomeric chain, the oligo-polyols have general and common characteristics and these characteristics are determined by the same analytical methods. These first common elements permit an unitary and general point of view on all oligo-polyols for polyurethanes. 

Functionality is the second important characteristic of an oligo-polyol and is defined as the number of hydroxyl groups/molecule of oligo-polyol. The functionality of an oligo-polyol is not very easy to determine. An old method is based on the determination of the conversion... 

As an immediate consequence, the oligo-polyols containing terminal primary hydroxyl groups are more reactive in the reaction with isocyanates than the oligo-polyols having only secondary hydroxyl groups. The primary hydroxyl content of an oligo-polyol is an important characteristic, because it is possible to determine the potential reactivity with isocyanates. 

All the oligo-polyols are used to build the polyurethane high MW structure in a reactive process, as a consequence of the oligo-polyols terminal hydroxyl group reaction with polyisocyanates. The reactivity of oligo-polyols in polyurethane fabrication is a very important practical characteristic. Reactivity is a measure of the reaction rate of an oligo-polyol with an isocyanate in order to make the final polyurethane polymer. One practical method is the measurement of viscosity, in time, by Brookfield Viscosity Test (BVT), especially used to determine the reactivity of ethylene oxide capped polyether polyols. Figure 3.12 shows the effect of the primary hydroxyl content upon the reactivity of ethylene-oxide capped polyether triols of MW of 5,000 daltons. 

To conclude, the common physico-chemical characteristics of oligo-polyols for polyurethanes determined by standard analytical methods are hydroxyl number, hydroxyl percentage, primary hydroxyl content, molecular weight, equivalent weight, molecular weight distribution, viscosity, specific gravity, acidity and colour (See Chapters 3.1-3.11). 

Of course, some oligo-polyols have specific and particular characteristics and these special characteristics will be presented in detail for each group of oligo-polyol. For example ... 

Summarising, no matter what their chemical structure, oligo-polyols have some general and common characteristics such as ... 

All oligo-polyols are low MW polymers, in the range characteristic for oligomers (MW < 10000 daltons). 

All oligo-polyols are characterised by general and common physico-chemical characteristics (see Chapter 3), determined by common standard test methods. 

The starters used frequently in the synthesis of oligo-polyols for elastic PU and some important characteristics of these starters for PU chemistry are presented in Table 4.1. 

Several general properties, characteristic to classical macromolecular chemistry, are strongly linked to the polyurethane structure, as a direct consequence of the oligo-polyol structure - these are [1, 2, 5, 9, 11] ... 

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. 

All oligo-polyols are characterised by the same physico-chemical characteristics, determined by the same common analytical methods ... 

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