Polyols hydroxyl number

Of course the hydroxyl number presented in Table 13.2 is a hypothetical one (the amines do not have hydroxyl groups), but it is very useful for the calculation of the final amino polyol hydroxyl number, after alkoxylation. 

Polyisocyanate Equivalent Weight % NCO Polyol Hydroxyl Number Molecular Weight... 

Hydroxyl Number. The molecular weight of polyether polyols for urethanes is usually expressed as its hydroxyl number or percent hydroxyl. When KOH (56,100 meg/mol) is the base, the hydroxyl number is defined as 56,100/equivalent weight (eq wt). Writing the equation as eq wt = 56,100/OH No. allows one to calculate the equivalents of polyol used in a urethane formulation, and then the amount of isocyanate required. The molecular weight can be calculated from these equations if the fiinctionahty, is known mol wt = / eq wt. 

The hydroxyl number can be deterrnined in a number of ways such as acetylation, phthalation, reaction with phenyl isocyanate, and ir and nmr methods. An imidazole-catalyzed phthalation has been used to measure the hydroxyl number for a number of commercial polyether polyols and compared (favorably) to ASTM D2849 (uncatalyzed phthalation) (99). The uncatalyzed method requires two hours at 98°C compared to 15 minutes at the same temperature. 

Example 5. Glycolysis of Polyurethanes with Propylene Oxide after Pretreatment with Ethanolamine.55 A rigid polyurethane foam (ca. 100 g) was dissolved in 30 g ethanolamine by heating. Excess ethanolamine was stripped, leaving a clear solution. Infrared and GPC analysis indicated that the clear solution obtained contained some residual polyurethane, aromatic polyurea, aliphatic polyols, aromatic amines, and N,N -bis(f -hydroxyethyljurea. Next the mixture was dissolved in 45 g propylene oxide and heated at 120°C in an autoclave for 2 h. The pressure increased to 40 psi and then fell to 30 psi at the end of the 2-h heating period. The product was a brown oil with a hydroxyl number of485. 

Fig. 22 Respirometry of vegetable oil-based polyurethanes made from the following polyols triolein-met arrowhead), soy-HF (filled square), soy-met 180 (open diamond), soy-met 206 (open circle), and linseed met (open square). Also shown is ESO/BF3 polymer (open triangle) and soybean oil control (filled circle). Temperature was increased from 30°C to 55°C on day 71. Note that hydroxyl number of 180 has the functionality of 3.3 and that of hydroxyl 206 is 4.0. Met refers to polyol made from ESO and methanol HF refers to polyol from hydroformylation and reduced ESO. Reproduced from [152] by permission of Journal of Polymers and the Environment...

ASTM Method D 4274-94, Standard Test Methods for Testing Polyurethane Raw Materials Determination of Hydroxyl Numbers of Polyols, ASTM, Philadelphia, PA, 1994. 

Infrared Spectroscopy. The following bands are seen in the ir spectrum of PPG 2970, 2940, 2880 cm-1 (C—H stretch, m) 1460,1375 cm-1 (C—H bend, m) 1100,1015 cm-1 (C—O stretch, m) of which the 2940 and 1015 band are specific. The latter are also present in copolymers of EO and PO. Absorptions due to unsaturated end groups are found at 1650 cm-1 (allyl ether) and 1672 cm-1 (1-propenyl ether). The O—H stretching band at 3470 cm-1 shows the greatest variation for different hydroxyl number polyols and has been used to estimate the hydroxyl number (169). 

J. Loertscher and F. Weesner, Determination of Hydroxyl Number in Polyols by Mid-Infrared Spectroscopy, Nicolet FT-IR Application Note (AN-9146), Nicolet Instrument Corp. 

Specification sheets will often give the equivalent weight of the polyol in terms of the hydroxyl number ("OH" value). The hydroxyl number is defined as "the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content of 1.0 grams of polyol." Manipulation of this definition gives the follow equation ... 

Sorbitol Polyol-Modified Isocyanurate Foam (71). This foam was prepared according to the following procedure. Potassium 2-ethylhex-anoate containing 4% water was used as the catalyst (soluble in polyether polyols). 94 g of sorbitol-based polyether polyol having a hydroxyl number of 490, 8.5 g of the potassium 2-ethylhexanoate, 120 g of tris(chloroethyl) phosphate, 5 g of silicone surfactant, and 90 g of... 

ASTM D 4274-88 Standard Method for Testing Polyurethane Polyol Raw Materials Determination Of Hydroxyl Number of Polyols, 9 pp (Conun D-20)... 

The hydroxyl number is very important for the synthesis of polyurethane. It is defined as the number of milligrams of potassium hydroxide equivalent to the hydroxyl content of one gram of the sample. The principle of the analytical method is that the hydroxyl group is esterified with a solution of phthalic anhydride in pyridine. The excess reagent is back-titrated with standard sodium hydroxide solution, and a blank is run on the reagents to determine the amount of anhydride consumed. The phenolphthalein is an indicator for the titrate. Because the color of recycled polyol is dark brown, the faint pink endpoint is not clear, so a potentiometric titrate can be applied. 

UrethHall [Hall], TM for polyester polyols for urethane systems that are fluid and pourable at room temperature and are based on chemistry completely different from the traditional adipate polyesters. Available in 25 different variations of glycol base, hydroxyl number, or molecular weight. 

A High Molecular Weight, Ethylene Oxide Capped Polyether Polyol with a Hydroxyl Number of 34. 

Polymer Polyol, 20% Solids, with a Hydroxyl Number of 28. 

The influence of those parameters on hydroxyl number, carboxyl number, and polyol yield are summarized in Tables II and III. 

Low copolymer to propylene oxide ratios make it obviously difficult to totally liquefy lignin, Table II. Such conditions, however, seem to favor polyols with low total hydroxyl numbers. The oxyalkylation reaction appears to require catalyzation by zinc chloride or base catalysts in concentrations of about 10% or less for successful completion. The presence of an initiator (ethylene glycol) helps completion of the reaction in particular when the unhydrolyzed copolymer is used as substrate (Table III). 

OH = hydroxyl number of oligo-polyol in mg KOH/g, Mn = number average molecular weight (g/mol), f = functionality, the number of OH groups/mol, and 56,100 = equivalent weight of KOH, in milligrams. 

For poly ether polyols an NMR method was elaborated for functionality determination [20]. The most usual and practical method for functionality determination is based on the assessment of the MW of an oligo-polyol, by a method applicable to low MW compounds (MW < 10,000 daltons), such as vapour pressure osmometry (VPO) or gel permeation chromatography (GPC), together with hydroxyl number determination. The functionality is calculated by using the fundamental equation 3.4 ... 

The MW of any oligo-polyol is calculated with formula 3.4 if the functionality (f) and the hydroxyl number (OH ) are known, in fact it is a particular case of MW determination by the quantitative analysis of the terminal functional groups, in our case the hydroxyl groups. Thus, a triol with an OH of 27 mg KOH/g has a calculated MW of 6,233 daltons, but a tetraol having the same OH, has a calculated MW of 8,311 daltons. Table 3.1 gives the values of the MW for oligo-polyols of different functionalities. 

The 19fluorine NMR method is one of the most accurate methods for primary hydroxyl determination. It is suitable for oligo-polyols (especially poly ether polyols) with hydroxyl numbers in the range 24-300 mg KOH/g and primary hydroxyl percentages in the range of 2 to 98%. 

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