Aromaticity Mannich polyols

Mannich polyols, aromatic polyester polyols, novolak-based polyols) lead, by the reaction with crude MDI, to very rigid polyurethane structures [2] (see Chapter 15). 

Mannich polyols is a very important group of aromatic polyols obtained by the alkoxylation with propylene oxide (PO) [(and/or ethylene oxide (EO)] of the Mannich bases obtained by classical Mannich reaction between phenols (for example phenol, p-nonylphenol), formaldehyde and alkanolamines (diethanolamine, diisopropanolamine, monoethanolamine, monoisopropanolamine and so on). Synthesis of Mannich polyols is divided into two important steps ... 

In the case of phenol, with the free para position, due to the interaction between the phenolic group (acidic) and the aminic nitrogen (basic) of the amino alcohol, the ortho position is occupied first [9]. After the synthesis of Mannich bases, the water resulting from the reaction and the water from the aqueous solution of formaldehyde is distilled under vacuum, at 90-125 °C (preferably in the range 90-100 °C). A low range of distillation temperatures is preferred in order to avoid the tendency of the Mannich base to condensate to superior oligomers (with 2-3 aromatic nuclei), which increase substantially the viscosity of Mannich base and, of course, of final Mannich polyol. The mechanism of the Mannich reaction is considered to be a two-step mechanism. In the first step the reaction between formaldehyde and the primary or secondary amine (reaction 15.2) takes place, with the formation of an immonium cation [7-9, 22, 23]. 

The Mannich polyols described are aromatic aminic polyols, the aromatic rings have a real contribution in improving the physico-mechanical, thermal and fire proofing properties of the resulting rigid polyurethane (PU) foams. The Mannich bases, for example the Mannich base resulting from one mol of nonyl-phenol, 2 mols of formaldehyde and 2 mols of... 

The aromaticity of a Mannich polyol is calculated with the following formula ... 

Mannich polyols are aromatic polyols, which confer excellent physico-mechanical, thermal and fire proofing properties to rigid PU foams. Mannich polyols, especially those based on p-nonyl phenol, have a very good compatibility with pentanes used as blowing agents (for example sucrose polyether polyols have a poor compatibility with pentanes, giving emulsions at normal concentrations for foaming, but not real solutions). 

From low MW oligo-polyols (400-1000 daltons polyethers, polyesters, Mannich polyols, aromatic polyesters, oleochemical polyols, etc.), are obtained rigid, hard polyurethane structures (rigid PU foams, wood substitutes, etc). 

Flame retardant rigid PU foams, due to their high aromaticity, and high crosslink density are easier to be obtain. An aromatic polyol has a supplementary contribution to improving the fire resistance (for example Mannich polyols, novolak polyols, triazinic polyols based... 

With amine initiators the so-called self-catalyzed polyols are obtained, which are used in the formulation of rigid spray foam systems. The rigidity or stiffness of a foam is increased by aromatic initiators, such as Mannich bases derived from phenol, phenolic resins, toluenediamine, or methylenedianiline (MDA). BASF/Dow have formed a venture into Mannich polyols for spray foam applications. 

A very interesting bromine aromatic polyol is obtained by the Mannich type reaction between 2,4 dibromophenol (or 2,6 dibromophenol) with diethanolamine and formaldehyde [28] or better still with oxazolidine [29], followed by the propoxylation of the resulting Mannich base with 2-3 mols of PO [28, 29] (reactions 18.6). 

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