Viscosity aminic polyols

As a general rule, all the aminic polyols obtained by the propoxylation of the amines discussed have very high viscosities. By the introduction of EO units the aminic polyol viscosities decrease substantially [4],... 

Aromatic amines such as o-TDA and MDA, give useless aminic polyols because of the high viscosities resulting from the direct propoxylation. 

Thus, aminic polyols of lower viscosities are obtained by the following three methods ... 

It was observed experimentally that by increasing the number of PO units per chain derived from one hydroxyl group there are obtained not only lower hydroxyl numbers but the viscosities of the resulting aminic polyols decrease significantly. The extension of the chains with PO is possible only after the addition of a catalyst, such as KOH, NaOH, low hindered tertiary amines or imidazoles. Utilisation of KOH and NaOH as catalysts needs a purification step. Using a low hindered amine as catalyst (trimethylamine, dimethyethanolamine, dimethylcyclohexylamine) the resulting polyols do not need any purification. 

Thus, by the propoxylation of DETA with around 8-10 mols of PO/mol of DETA, by using dimethylethanolamine as catalyst, aminic polyols of low hydroxyl number (390-420 mg KOH/g) are obtained, with low viscosity of around 6,000-9,000 mPa-s, at 25 °C [1,10,11] ... 

By the reaction of 4-5 mols of EO with one mol of DETA, followed by a catalysed propoxylation step, it is possible to obtain aminic polyols with a functionality of 5 OH groups/mol with a high hydroxyl number and convenient low viscosities (equation 14.5). 

By the introduction of internal EO units (25-30% internal EO) it was possible to obtain an o-TDA-based aminic polyol with an acceptable viscosity, of around 10,000-15,000 mPa-s, at 25 °C (reaction 14.8.) [4]. 

The same strong effect on the viscosity decrease was observed by the introduction of an internal poly [EO] block in the case of synthesis of aromatic aminic polyols derived from methylenedianiline (MDA), a precursor of diphenylmethane diisocyanate (MDI) [2, 5, 6] ... 

This method of viscosity decrease by introduction of internal EO units is very efficient for reusing wastes resulting from MDA fabrication, which have superior oligomers with 3, 4 or 5 aromatic nuclei (reaction 14.9). Propoxylation of these MDA wastes gives extremely viscous aminic polyols [2]. 

Highly aromatic and high functionality aminic polyols, of very convenient viscosities (15,000-25,000 mPa-s at 25 °C) are obtained. Similar effects of viscosity decrease were obtained by using as monomers a mixture of PO with EO (15-25% EO). 

The third method to decrease the viscosity of aminic polyols is the alkoxylation of a mixture between a polyamine (which leads to very viscous polyols) with a monoamine, such as monoethanolamine, diethanolamine, diisopropanolamine or monoisopropanolamine, (which lead to fluid polyols). The quantity of monoamine is calculated so as not to affect markedly the functionality of the final aminic polyol. 

Polybutadienes, polycaprolactones, polycarbonates, and amine-terminated polyethers (ATPEs) are shown in Scheme 4.4 as examples of other commercially available polyols. They are all specialty materials, used in situations where specific property profiles are required. For example, ATPEs are utilized in spray-applied elastomers where fast-reacting, high-molecular-weight polyamines give quick gel times and rapid viscosity buildup. Polycarbonates are used for implantation devices because polyuredtanes based on them perform best in this very demanding environment. Polycaprolactones and polybutadienes may be chosen for applications which require exceptional light stability, hydrolysis resistance, and/or low-temperature flexibility. 

An amine-terminated poly ether (ATPE) is prepared as follows. Charge poly(tetramethylene oxide) diol (PolyTHF 1000, BASF, 75.96 g, 0.0759 m) to a 500-mL three-neck round-bottom flask fitted with a thermocouple, a mechanical stirrer, and a vacuum port. Add tert-butylacetoacetate (24.04 g, 0.1582 m) and apply vacuum. Heat at 175° C for 4 h, Fourier transform infrared (FTIR) analysis should indicate complete loss of the polyol OH absorption at 3300 cm. The room temperature viscosity of the product should be about 520 mPa-s. React this acetoacetylated product (85.5 g, 0.0649 m) with cyclohexylamine (14.5 g, 0.1465 m) at 110° C under vacuum for several hours. Cool the resultant cyclohexylaminocrotonate poly ether product to room temperature (1790 mPa-s at room temperature). 

The one-shot process is used for flexible and rigid foams. In the case of slabstock foams, the ingredients are separately supplied to the mixing head. In order to adjust viscosity and mixing accuracy, some of the ingredients, such as polyol and tin catalyst, water and amine catalyst, are pre-mixed. 

The advantages of these aromatic polyesters are lower cost than conventional polyether polyols, better flame retardance, and high-temperature resistence. However, their disadvantages include compatibility problems with chlorofluorocarbons and quality deviations in viscosity and hydroxyl values. In order to improve the compatibility problems, amine-based polyether polyols have been blended. 

The structure (6.8) is another type of NAD formed in situ by transfer reaction with the tertiary amine type polyethers. Addition of a high molecular weight polyether initiated by an alkanolamine, ethylene diamine, N-methyl substituted propylene diamine, or N,N dimethyl dipropylene diamines in the polyether polyol used for grafting leads to the formation of very stable polymeric dispersions [37]. The solid fraction has particles of low median diameter (<1.5 pm). The resulting polymer polyols have low viscosities which give good stabilisation of the polymeric dispersion. 

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 alkoxylation of lignin is possible in a solvent (dimethylformamide, N-methylpyrrolidone or in liquid PO [20]). A process using a lignin-glycerol mixture (3 1) in a polyether polyol based on lignin was developed [20]. The catalysts of this reaction are KOH, but a tertiary amine, such as dimethylaminoethanol is preferred. By alkoxylation with a PO-EO mixture (e.g., 18-25% ethylene oxide EO) a totally liquid dark-brown lignin-based polyether polyol with a viscosity in the range 4,700-8,000 mPa-s at 25 °C, with an hydroxyl number... 

Metal compounds, and especially organotin compounds, are much more efficient catalysts than the amines, especially for the hydroxyl/isocyanate reaction. This allows the polymer-forming polyol/isocyanate reaction to proceed at a sufficient rate to increase viscosity rapidly to a state where gas is effectively trapped, as well as to develop enough gel strength to present any cell structure from collapsing after gas evolution has ceased. 

The most suitable polyols are prepared via a coinitiator technique whereby optimal functionality (4-5), hydroxyl number (330-430), use viscosity (2,500 cps max) and reactivity are achieved. Comparative letbora-tory evaluations have shown that sucrose amine-based polyols are inherently more compatible with polymeric isocyanates than other polyols. They have also demonstrated excellent flow and demolding characteristics and produce hard but not brittle structural foams. 

Low-molecular-weight low-viscosity hydroxylated polyesters can be used for this purpose and can be formulated from glycols, higher polyols and poly basic acids. The HS fully alkylated amines fit well into this type of coating system because they have low molecular weight, are of moderate viscosity, carry little or no solvent and thus offer many advantages in HS formulations. 

A two-stage method of waste polyurethane degradation is described in [79]. In the first stage, scission of the polyurethane chain takes place at a temperature of 120°C in the presence of dialkanolamine and metal hydroxide e.g., KOH). Under these conditions, the reaction products include polyols, aromatic amines, short-chain ureas, and urea derivatives. The second stage is based on the alcox-ylation of the hydroxyl groups and the primary and secondary amine groups, e.g., by the use of propylene oxide. In this way, polyols with a hydroxyl number of 156-271 mg KOH/g and viscosity within the range of 1950-57 000 mPa s can be obtained. The flexible foams prepared from recycled polyols revealed favorable mechanical properties. 

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