Polyester polyols functionality

MDl polyester isocyanate prepolymers (addition products of MDl and a di- or higher functional polyester polyol)... 

Features High functionality polyester polyol produces foams with extreme solv. resist., good bond strength, adhesion, and tack without creep Properties Gardner 0+ liq. m.w. 2600 dens. 10.0 Ib/gal vise. 24,000 cps acid no. 0.5 hyd. no. 90 Lexorez 3130-35 [Inolex]... 

Polyester polyols are based on saturated aHphatic or aromatic carboxyHc acids and diols or mixtures of diols. The carboxyHc acid of choice is adipic acid (qv) because of its favorable cost/performance ratio. For elastomers, linear polyester polyols of ca 2000 mol wt are preferred. Branched polyester polyols, formulated from higher functional glycols, are used for foam and coatings appHcations. Phthalates and terephthalates are also used. 

Polyester polyols (Scheme 4.4) are prepared by condensation polymerization of dicarboxylic acids and diols. An excess of diol ensures OH functional product, minimizing die possibility of residual acid groups which react with isocyanates to generate C02 and act as inhibitors in catalyzed urethane reactions. The reactants are heated at 200-230°C under vacuum to remove the water by-product and drive the reaction to completion. The most common coreactants include adipic... 

Isocyanates react with carboxylic acids to form amides, ureas, anhydrides, and carbon dioxide, depending on reaction conditions and the structure of the starting materials (Scheme 4.13). Aliphatic isocyanates more readily give amides. Aromatic isocyanates tend to react with carboxylic acids to first generate anhydrides and ureas, which at elevated temperatures (ca. 160°C) may further react to give amides. In practice, the isocyanate reaction with carboxylic acid is rarely utilized deliberately but can be an unwanted side reaction resulting from residual C02H functionality in polyester polyols. 

These results have been fit to experimental data obtained for the reaction between a diisocyanate and a trifunctional polyester polyol, catalyzed by dibutyltindilaurate, in our laboratory RIM machine (Figure 2). No phase separation occurs during this reaction. Reaction order, n, activation energy, Ea, and the preexponential factor. A, were taken as adjustable parameters to fit adiabatic temperature rise data. Typical comparison between the experimental and numerical results are shown in Figure 7. The fit is quite satisfactory and gives reasonable values for the fit parameters. Figure 8 shows how fractional conversion of diisocyanate is predicted to vary as a function of time at the centerline and at the mold wall (remember that molecular diffusion has been assumed to be negligible). 

Linear polyols of various molecular weights can be used in the chain extension of prepolymers. Their main use is to adjust the hardness of the final compound. They act as a reactive plasticizer, and their functionality and molecular weight must be taken into account in the curative calculations. Either polyether or polyester polyols can be used. The most important point is that they must be dry. 

Polyether Polyols. The major polyols for preparing various urethane foams are polyether polyols. Polyester polyols are used only in specific applications. The advantages of polyether polyols are choice of functionality and equivalent weight the viscosities are lower than those of conventional polyesters production costs are cheaper than for aliphatic polyesters and resulting foams are hydrolysis-resistant. 

The polyols which function as modifiers include ethylene glycols, 1,4-butanediol, polyether polyols and polyester polyols. In recent years aromatic polyesters prepared from reclaimed PET (polytetraethylene terephthalate) or the distillation residue of DMT (dimethylterephthalate) have appeared as modifiers for urethane-modified isocyanurate foams (73, 78). These aromatic polyesters are produced by the transesterification of reclaimed PET or DMT distillation residue. 

Polyester polyols are the esters of dicarboxylic acids with bivalent alcohols, resulting in intermediate products with two terminal or functional OH groups (diol). The dicarboxylic acids may be either aliphatic or aromatic, which is also true of the... 

To determine the average hydroxyl functionality of a sample of polyester polyol of M = 3,000 about 1 g of the dry sample was treated with bromoacetyl bromide (BrCH2COBr) to convert hydroxyl to bromoacetyl end groups. The treated polymer was found to contain 4.88% Br by elemental analysis. Estimate the average number of hydroxyl groups on each molecule of the polyol. 

By using, together with a diol, a triol such as TMP or glycerol it is possible to obtain polyesters with a functionality (f) higher than 2 OH groups/mol, situated in the range of 2-3 OH groups/mol. These polyester polyols are used for flexible PU foam fabrication. Flexible PU foams based on polyester polyols have a unique property their clickability (capacity to be easily cut) and are used in laminates for textile industry. 

Chapter 12.5). Polyester polyols in reality, have the theoretical functionality, which is a great advantage for many polyurethane applications. For polyester diols the functionality is 2 OH groups/mol. This structural aspect results in the polyester diols giving PU elastomers with excellent physico-mechanical properties, superior to all polypropylene glycols obtained by anionic PO polymerisation. 

It is very clear, that the reaction between a dicarboxylic acid with a glycol always results in a polyester diol, the functionality being exactly 2 OH groups/mol. The functionality of a branched polyester polyol is calculated by the Chang equation [22] ... 

The advantage of CPL-based polyester polyols is that the final functionality of the resulting oligo-polyol is identical to the functionality of the starter used and, generally, no side reactions were observed to markedly affect the functionality. 

The development of highly crosslinked rigid polyisocyanurate foams opens an excellent area of applications for polyester polyols [4-8]. The required polyols do not need high functionality and the plasticising effect of polyester structures is extremely beneficial for these highly crosslinked systems [6]. The first polyester polyols used for these applications were low viscosity polycondensation products of AA with ethyleneglycol (EG) or diethyleneglycol modified with phthalic anhydride or triols. 

The highly crosslinked structure is not derived from polyester polyol, which has a low functionality (f = 2-3 OH groups/mol), but is derived from the isocyanurate rings generated by the trimerisation of the excess of -NCO groups. 

Of course the thermal stability and char yield depend on the polyol structure too and the aromatic polyols are superior to aliphatic polyols from this point of view. This is the reason for the extremely rapid growth of aromatic polyester polyols, of low functionality, low viscosity and low cost. 

The bottom residues from DMT fabrication are benzyl and methyl esters of dicarboxylic and tricarboxylic acids with biphenyl or triphenyl structures together with DMT [4, 6. By the transesterification reactions of these complex ester residues with diethyleneglycol (DEG), aromatic polyester polyols with a functionality in the range 22-23 OH groups/mol are obtained. 

PET wastes, proved to be an excellent raw material for low cost aromatic polyester polyols. By transesterification with DEG and (or) propylene glycol or dipropyleneglycol (DPG), liquid, low viscosity and low functionality aromatic polyester polyols were obtained. Due to the low cost, DEG is the preferred glycol for transesterification (reaction 16.3) [4, 6-8, 12]. 

Polyester polyols with equivalent weight of 167, functionality of 2 OH groups/mol, hydroxyl number of 310-350 mg KOH/g and viscosity of 1,300-3,000 mPa-s at 25 °C, are used in thermal insulation of appliances. The initial ratio between DEG and PET used in synthesis, followed by the utilisation of one of the previously mentioned procedures avoids solidification (section 16.2, a-e), and means that a large range of aromatic polyester polyols, having various hydroxyl numbers, functionalities and aromaticity can be obtained. 

Polyester polyols for rigid PU foams can be obtained by ring opening polymerisation of s-caprolactone, initiated by various polyols such as a-methyl glucoside, sorbitol, pentaerythritol or trimethylolpropane. A polyester polyol derived from penteaerythritol has the following properties functionality of 4 OH groups/mol, hydroxyl number of 600 mg KOH/g, acid number of around 2 mg KOH/g and a of viscosity 7,000 mPa-s, at 25 °C (reaction 16.8) [2, 33-35]. 

Thus, by the propoxylation of the reaction product of one mol of maleic anhydride with one mol of glycerol, aliphatic polyester polyols having functionalities greater than 3, in the range of 3-4 OH groups/mol are obtained. The functionality of greater than 3 is created in situ by the addition of an hydroxyl group to the double bond of the maleic esters formed (reactions 16.9). 

The most important structures of rigid polyester polyols presented in this chapter (Chapter 4.4) are the low functionality aromatic polyester polyols with terephthalic or phthalic structures, used for PU/PIR rigid foams. 

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