Polyurethane catalyst

Sorbitol is manufactured by the reduction of glucose in aqueous solution using hydrogen with a nickel catalyst. It is used in the manufacture of ascorbic acid (vitamin C), various surface active agents, foodstuffs, pharmaceuticals, cosmetics, dentifrices, adhesives, polyurethane foams, etc. 

As a class of compounds, nitriles have broad commercial utility that includes their use as solvents, feedstocks, pharmaceuticals, catalysts, and pesticides. The versatile reactivity of organonitnles arises both from the reactivity of the C=N bond, and from the abiHty of the cyano substituent to activate adjacent bonds, especially C—H bonds. Nitriles can be used to prepare amines, amides, amidines, carboxyHc acids and esters, aldehydes, ketones, large-ring cycHc ketones, imines, heterocycles, orthoesters, and other compounds. Some of the more common transformations involve hydrolysis or alcoholysis to produce amides, acids and esters, and hydrogenation to produce amines, which are intermediates for the production of polyurethanes and polyamides. An extensive review on hydrogenation of nitriles has been recendy pubHshed (10). 

In the presence of acid catalysts, butynediol and aldehydes (47) or acetals (48) give polymeric acetals, useful intermediates for acetylenic polyurethanes suitable for high energy soHd propellants. 

The physical properties of polyurethane adhesives result from a special form of phase separation which occurs in the cross-linked polyurethane stmcture. The urethane portions of polyurethanes tend to separate from the polyol portion of the resin, providing good shear strength, good low temperature flexibiUty, and high peel strength. Catalysts such as dibutyltin dilaurate [77-58-7], stannous octoate [1912-83-0], l,4-diazabicyclo[2.2.2]octane... 

Acetylene is condensed with carbonyl compounds to give a wide variety of products, some of which are the substrates for the preparation of families of derivatives. The most commercially significant reaction is the condensation of acetylene with formaldehyde. The reaction does not proceed well with base catalysis which works well with other carbonyl compounds and it was discovered by Reppe (33) that acetylene under pressure (304 kPa (3 atm), or above) reacts smoothly with formaldehyde at 100°C in the presence of a copper acetyUde complex catalyst. The reaction can be controlled to give either propargyl alcohol or butynediol (see Acetylene-DERIVED chemicals). 2-Butyne-l,4-diol, its hydroxyethyl ethers, and propargyl alcohol are used as corrosion inhibitors. 2,3-Dibromo-2-butene-l,4-diol is used as a flame retardant in polyurethane and other polymer systems (see Bromine compounds Elame retardants). 

Catalysts. Mercury is or has been used in the catalysis (qv) of various plastics, including polyurethane [26778-67-6] poly(vinyl chloride) [9002-86-2] and poly(vinyl acetate) [9003-20-7]. Most poly(vinyl chloride) and poly(vinyl acetate) is manufactured by processes that do not use mercury (3). 

Organic Reactions. Nitric acid is used extensively ia iadustry to nitrate aHphatic and aromatic compounds (21). In many iastances nitration requires the use of sulfuric acid as a dehydrating agent or catalyst the extent of nitration achieved depends on the concentration of nitric and sulfuric acids used. This is of iadustrial importance ia the manufacture of nitrobenzene and dinitrotoluene, which are iatermediates ia the manufacture of polyurethanes. Trinitrotoluene (TNT) is an explosive. Various isomers of mononitrotoluene are used to make optical brighteners, herbicides (qv), and iasecticides. Such nitrations are generally attributed to the presence of the nitronium ion, NO2, the concentration of which iacreases with acid strength (see Nitration). 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

Amine catalysts for polyurethane appHcations are sold by Air Products (Dabco), Abbott (Polycat), Kao Corporation (Kaolizer), Tosoh Corporation (Toyocat), and Union Carbide (Niax). 

Some of the chemicals used in the production of polyurethanes, such as the highly reactive isocyanates and tertiary amine catalysts, must be handled with caution. The other polyurethane ingredients, polyols and surfactants, are relatively inert materials having low toxicity. 

Tertiary Amine Catalysts. The Hquid tertiary aHphatic amines used as catalysts in the manufacture of polyurethanes can cause contact dermatitis and severe damage to the eye. Inhalation can produce moderate to severe irritation of the upper respiratory tracts and the lungs. Ventilation, protective clothing, and safety glasses are mandatory when handling these chemicals. 

Metal salts of neodecanoic acid have also been used as catalysts in the preparation of polymers. For example, bismuth, calcium, barium, and 2kconium neodecanoates have been used as catalysts in the formation of polyurethane elastomers (91,92). Magnesium neodecanoate [57453-97-1] is one component of a catalyst system for the preparation of polyolefins (93) vanadium, cobalt, copper, or kon neodecanoates have been used as curing catalysts for conjugated-diene butyl elastomers (94). 

Other Octoate Uses. Metal octoates are also used as driers in printing inks. Another appHcation of octoates includes the use of the aluminum salt to gel paint. Stannous, dibutyltin, and bismuth carboxylates find appHcation as catalysts in polyurethane foam appHcations in order to obtain a reaction efficiency suitable for industrial production. In polyurethane foam manufacture the relative rate of polymeriza tion and gas foaming reactions must be controlled so that the setting of the polymer coincides with the maximum expansion of the foam. 

There is persisting interest in nylon-RIM materials as alternatives to polyurethane-RIM. Advantages of the nylon materials are the better shelf life and lower viscosity of the reaction components, ability to mould thick-walled articles, absence of a need for mould lubrication and the ability to avoid using isocyanates with their associated hazards. The main disadvantages of nylon-RIM are the need to have heated storage tanks and elevated temperature reactions, difficulties in catalyst handling and the high water absorption of the product. Possible markets include exterior car body components and appliance and business machine components. 

Over the years many blends of polyurethanes with other polymers have been prepared. One recent example is the blending of polyurethane intermediates with methyl methacrylate monomer and some unsaturated polyester resin. With a suitable balance of catalysts and initiators, addition and rearrangement reactions occur simultaneously but independently to give interpenetrating polymer networks. The use of the acrylic monomer lowers cost and viscosity whilst blends with 20% (MMA + polyester) have a superior impact strength. 

The first urethane reaction in Fig. 1 is used in two major ways in adhesives. In one case, a two-component adhesive usually employs a polyol and polyisocyanate with catalyst. This can react at room temperature to form the polyurethane. The second use of this reaction is to make an isocyanate-terminated prepolymer. Reacting a stoichiometric excess of isocyanate with polyol can produce an isocyanate-terminated prepolymer. A prepolymer is often made with an NCO/OH ratio of 2.0, as shown below, but the isocyanate ratio can range from 1.4 to over 8.0, depending upon the application ... 

Initially, the water slowly reacts with the isocyanate. However, the reaction can be catalyzed with an appropriate catalyst, such as dibutyltin dilaurate or a morpholine tertiary amine catalyst. The isocyanate will react with water to form a carbamic acid, which is unstable and splits off carbon dioxide, to produce a terminal amine end group (see p. 76 in [6]). This amine then reacts with more isocyanate-terminated prepolymer, as shown above, to form a polyurea. This process repeats itself, building up molecular weight and curing to become a polyurea-polyurethane adhesive. 

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