Polyol equivalent weight

In order to complete our model, we need to know the soft phase modulus, Egp. It depends on several factors, most notably polyol equivalent weight. Eg, polyol functionality, fp, and polyol glass transition temperature, Tgp. At temperatm-es substantially above (elastomeric region), the modulus of the soft phase can be described using network elasticity models [57-59] ... 

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. 

Polyurethane adhesives are known for excellent adhesion, flexibihty, toughness, high cohesive strength, and fast cure rates. Polyurethane adhesives rely on the curing of multifunctional isocyanate-terrninated prepolymers with moisture or on the reaction with the substrate, eg, wood and ceUulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before apphcation. Two-component polyurethane systems are also used as hot-melt adhesives. 

The reactor was purged with nitrogen and heated to 50 °C under 20 torr vacuum. The vacuum was broken and 500 ppm of stannous octoate catalyst obtained from City Chemical was added. The methanol was stripped under 20 torr vacuum at 195 °C for 4-6 hours yielding a viscous light yellow natural oil polyol with an equivalent weight of 660. 

It is important to be aware of the chemical effects of isocyanates. The polynre-thanes you will develop will be combinations of polyols and isocyanates. The ratio of the two compounds will in pait dictate both the physical and chemical properties of the product. As a general rule, the isocyanates are hard segments that impart rigidity to the polymer. The polyol is the so-called soft segment. The various molecular weights (more correctly equivalent weights available in the form of polymeric MDIs) provide certain advantages. Table 2.2 lists a few commercially available polyisocyanates and their physical properties. 

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 ... 

In the present work, however, a more controlled oxypropylation process (12) carried out in solution and at atmospheric pressure was developed and used to convert EGG into a liquid polyol. This polyol, with the idealized structure (6) in which n = 3, had an equivalent weight toward MDI of 293 g-mol-1. 

In this study, the use of a PM polyol as a rubber modifier for a highly crosslinked, polyurethane resin (T = 150 °C) was assessed again in comparison with an oil-based PB polyol. The polyurethane resin matrix was formed from pure MDI and a polyol blend comprising a polyoxypropylene triol, LHT240 (Union Carbide) of equivalent weight 227.6 g-mol"1, and trimethylol propane,... 

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 catalyst makes it possible to product outstandingly high-equivalent-weight polyether polyols, e.g., about 10,000. In other words, polyether diols of 20,000 molecular weight and polyether triols of 30,000 molecular weight can be produced. 

Urethane foams can be classified into two principle types, i.e., flexible and rigid foams. In some cases, flexible foams can be further subdivided into flexible and semi-flexible (or semi-rigid) foams. The differences in physical properties of the two foams are mainly due to the differences in molecular weight per cross-link, the equivalent weight and functionality of the polyols, and the type and ctionality of the isocyanate. 

These foams can be prepared by the proper choice of equivalent weight and functionality of the polyols employed. Polyisocyanates can be considered as the joining agents of the polyols. A rough classification of the three kinds of foams based on the type of polyols used is shown in Table 14. 

To this liquid mixture was added a mixture of 50 parts by weight (0.473 equivalent) of a polyol of equivalent weight 105.6 (the adduct of propylene oxide and a mixture of polyamines containing 50% by weight of methylenedianiline obtained by the acid condensation of aniline and formaldehyde) 50 parts by weight of dimethyl sulfoxide and 10 parts by weight of a silicone surfactant. 

Preparation of the polymers was carried out by a two step method. First, MDI prepolymers were prepared in a 5 liter round bottom flask equipped with a stirrer, thermometer, addition funnel, and nitroggn inlet. The dried polyols were added dropwise tg MDI at 75°C and the reaction temperature was maintained at 85°C. The mole ratios of MDI to polyol listed in Table II gave prepolymers containing 18.67% free NCO groups by weight or an isocyanate equivalent weight of 225. In the case of prepolymers 2 and 4, the DPG was added first and then the 2000 molecular weight polyol was added. 

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