Catalysts polyisocyanates

BPA epoxy resins can be cross-linked by reaction of their hydroxyl groups with MF and UF resins are used. Amine salts of a sulfonic acid are used as latent catalysts. Polyisocyanates also cross-link the hydroxyl groups of epoxy resins. 

Foam may be made from such polycaprolactones by reaction with polyisocyanates in the presence of tin catalysts. 

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 ... 

The pharmacological activities of other derivatives of these ring systems are examined intensively. Whereas other representatives of the above ring systems are patented as photographic sensitizers, catalysts for curing polyisocyanates, or dyes for acrylic nylon, polyester filters, and photographic material. 

In the single-stage production of polyurethanes, di-, tri-, or polyisocyanates are mixed directly with molecules containing two or more reactive hydrogen atoms, such as diols, diamines, and dicarboxylic acids. We typically increase the reaction rate by adding amine or organotin based catalysts. The reaction normally occurs rapidly, evolving much heat. In order to ensure... 

Polyurethane foam Natural oil polyol, water, and surfactants were weighed into a 1 quart metal cup and premixed for 15 seconds at 1800 rpm using a pin type mixer. The catalyst was added and the mixture stirred an additional 15 seconds at 1800 rpm. The polyisocyanate was then added and the mixture stirred at 2400 rpm for 3 seconds and immediately transferred to a 15 x 15 x 10 wooden box lined with a polyethylene bag. The buns were allowed to cure overnight before testing. 

Polyols and polyisocyanates are major ingredients for polyurethane (PU)-based composite propellants in addition to chain extenders and catalysts etc. A brief description on these materials is considered necessary in order to understand the chemistry of composite propellants in a better way. Polyols are the largest group of raw materials for PUs. The properties of PUs/PU products are largely determined by their chemical composition and molecular mass. They may be broadly classified [87] as ... 

The methyl methylphosphonate quatemery salt 695 was patented as catalyst in curing of polyisocyanate (85GEP3328662). The 2-phenyl derivative of hexahydropyrido[l,2-a]pyrimidine (696) was patented as a catalyst for curing of blocked isocyanate-terminated polycarbonate (87EUP247692). Pyrido[l,2-a]pyrimidine-8-nitrile derivatives were... 

Reactions with Isocyanates, TYZOR TPT catalyzes the trimerization of isocyanates and polyisocyanates to isocyanurates and polyisocyanurates (38). Titanium alkoxides of the type Cl3TiOR initiate the living polymerization of isocyanates. Polyisocyanates possessing controlled molecular weights and narrow polydispersities can be synthesized using these catalysts (39) ... 

Reaction Injection Molding. RIM mixes polyol, polyamine, polyisocyanate, and strong catalyst, and injects the mixture rapidly into a mold, where it cures rapidly to form large parts very economically. It is used primarily for producing front ends and other large parts of autos. 

A recent innovation in in-situ microencapsulation is the development of acid-triggered release of pesticide from the microcapsules [12]. Diols and aldehydes are reacted to form an acid labile acetal moiety. The acetal is then reacted with isocyanate to create a prepolymer. The prepolymer is a polyisocyanate cmitaining the acid labile moiety and suitable for in-situ shellwall polymerization. The prepolymer is dissolved into a pesticide, emulsified into water, and shellwall formed in-situ. Under alkaline or neutral pH conditions in a container, the insecticide is safely contained in the microcapsules. Acid could be added to the spray tank to rapidly release capsule contents prior to application. Alternate shellwall chemistry for in-situ microencapsulation utilizes etherified urea-formaldehyde prepolymers in the oil phase that are self-condensed with acid catalyst to produce encapsulating aminoplast shellwalls [13]. This process does not have the problem of continuing CO2 evolution. Water-soluble urea-formaldehyde and melamine-formaldehyde prepolymers can be selected to microencapsulate water or aqueous solutions [14]. 

The major raw materials for making isocyanate-based foams include the following compounds polyisocyanates, polyols, catalysts, blowing agents, surfactants, epoxides, and flame retardants. 

Preparation. Polyurethane foams (often referred to as urethane foams) are prepared by the reaction of a polyisocyanate with a polyol in the presence of a blowing agent, a surfactant, and a catalyst without external heating of the foaming system. The principle of preparation of urethane foams is based on the simultaneous occurrence of two reactions, i.e., polyurethane formation and gas generation in the presence of catalyst and surfactant, as shown below ... 

In recent years, the ban on the use of CFCs resulted in major changes in foam formulations. A number of studies were carried out on the use of 100% water-blown foams for both rigid and flexible foams. These studies required modifications or improvements in raw materials, e.g., polyisocyanates, polyols, catalysts and surfactants. 

In most cases semi-rigid urethane foams are produced by using two-component systems, that is component A (polyisocyanate component) and component B (blend of the remaining ingredients, i.e., polyol, blowing agent, catalyst and surfactant). 

Example (1) Unsaturated monoalcohol (acryloesterol) and styrene monomer are reacted with a polyisocyanate in the presence of a urethane catalyst and a radical polymerization catalyst to form hybrid resins (52). Styrene monomer acts as a crosslinker and at the same time, acts also as a reactive diluent. The trade name of a commercial product of such systems is Arimax (Ashland Chemical) (107). 

The polyisocyanates used for preparing carbodiimide foams include TDl, TDl-based prepolymers, liquid-MDl oligomers and polymeric isocyanates. Many catalysts for producing carbodiimide foams have been disclosed in the patent literature. Some of these are shown in Table 13. 

Polyurethane Foams. Rigid polyurethane foam can be prepared by the reaction of a polyisocyanate, a polyol, a blowing agent, a catalyst and a surfactant. Detailed explanation of these foams are described in the sections on Rigid Urethane Foams and Miscellaneous Urethane Foams earlier in this chapter. 

Urethane-Modified Isocyanurate Foams. Urethane-modified isocyanurate foams are prepared by the trimerization of a polyisocyanate in the presence of a polyol, a trimerization catalyst, a blowing agent, and a surfactant. The foams have high flame and temperature resistance. The combined use of an isocyanurate foam and glass fiber not only improves the physical properties, e.g., flexural strength, friability, etc. but it also improves the flame resistance because the char formed from the foam acts as thermal barrier and protects it from flame and heat. This type of composite, therefore, is widely used for buUding applications in the U.S.A. Urethane-modified isocyanurate foam systems have also been used in the SRIM process (26, 36, 37). 

The nse of organotin catalysts in secondary amine fnnctional polyaspartate-polyisocyanate cross-linked coatings has shown to improve the potlife of the formulation. 

Polyurethane hydrogels are prepared by reaction of a polyisocyanate with polyethyleneglycol. These hydrogels can swell with water and are used in medical applications, such as wound dressings. Although dialkyltin catalysts are claimed in this application, the use of organotin compounds in medical applications with potential contact with blood is questionable, and they are probably not the safest catalysts for this application. 

Polyurethanes are formed when a diisocyanate (or polyisocyanate) is reacted with hydroxyl groups at a molar ratio of 2 or higher (isocyanate hydroxyl). When the polyol and polyisocyanate are combined in the presence of a suitable catalyst, the exothermic polymerization reaction begins spontaneously. This type of synthesis is an addition polymerization. Most polyols and polyisocyanates used for manufacturing PUs are liquid at standard room temperature. Industrially, the PU synthesis reaction is rapid, and the product is a solid polymer. The reaction rate can be varied significantly by changing the catalyst type and concentration, facilitating the use of PUs in a variety of applications. ... 

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