Sealants urethane

Urethane sealants Urethane systems Urethane TPE Urethritis, nonspecific... 

The first step in formulating a urethane sealant is to prepare what is commonly called the prepolymer, typically by reaction of a hydroxy-terrninated polyether with a stoichiometric amount of a diisocyanate. Each hydroxy group reacts with one end of every diisocyanate molecule. 

One-part urethane sealants (Table 3) are more compHcated to formulate on account of an undesirable side reaction between the prepolymer s isocyanate end and water vapor which generates carbon dioxide. If this occurs, the sealant may develop voids or bubbles. One way to avoid this reaction is to block the isocyanate end with phenol and use a diketamine to initiate cure. Once exposed to moisture, the diketamine forms a diamine and a ketone. The diamine reacts with the isocyanate end on the prepolymer, creating a cross-link (10). Other blocking agents, such as ethyl malonate, are also used (11). Catalysts commonly used in urethane formulations are tin carboxylates and bismuth salts. Mercury salt catalysts were popular in early formulations, but have been replaced by tin and bismuth compounds. 

Table 3. Typical One-Part Urethane Sealant Formulation ...

Urethane sealants have good inherent adhesion to most substrates, but silane adhesion promoters are often used to improve this adhesion. Epoxy-, amino-, and mercapto-functional silanes are the most common because of their dual reactive nature. The silane end can react with surface hydroxyls the epoxy, amino, or mercapto end can react with the isocyanate. 

Adhesion promoting silanes are often added to improve adhesion to various substrates. As is the case with urethane sealants, silanes with a dual-reactive nature are typically used. Examples of such silanes are mercapto- and epoxy-functional silanes. Organic titanates may also be used. 

Frisch, Jr., K., Sealants and Caulks II — Short Course, Urethane Sealants. Adhesives and Sealants Council, Ine., 1994. 

One-part solvent-releasing butyl sealant formulation, 22 43t One-part urethane sealants, 22 36-37 One-pass clarifier, 22 61 One-photon absorption, 77 455 One-pot oxidation polymerization, 23 713 One-stage separation plants, 75 840 One-step cameras/processors, 79 276-278 One-step Ziegler process, 77 715-718 One-way memory, of shape-memory alloys, 22 341, 345-346... 

Polybutadiene (PB), 9 558 14 246 24 703 commercial block copolymers, 7 648t oxygen permeability at 25°C, 3 400 physical properties of, 4 376t in rubber compounding, 21 764-765 synthesis, 4 375-377 in tire compounding, 21 807 nel-Polybutadiene, 7 610t Polybutadiene-based urethane sealants, 22 36... 

Polyester-based urethane sealants, 22 36 Polyester block copolymers, commercial, 24 707-708... 

Polythiocarbamates, 23 735-738 Polythiocarbonates, 23 626, 725-729 thermal stability of, 23 726-727 Polythioesters, 23 729-732 preparation of, 23 730-731 Polythioether-based urethane sealants, 22 36... 

Although polyethers are the main building blocks of the prepolymer, other materials such as polyesters, polythioethers, and polybutadienes are also used. Most urethanes use blends of polymers to achieve desired properties. Urethane sealants have pood inherent adhesion to most substrates, but silane adhesion promoters are often used to unprove this adhesion,... 

Details of various joints are given in the discussion on polysulphide sealants (section 7.3) and silicone sealants (section 6.3). The same criteria are applicable in the case of urethane sealants, with the exception of glazing joints. 

Evans, R.N. and Greene, R.B. (1982) Urethane sealants for concrete structures, in Joint Sealing Systems for Concrete Structures, volume 2, publication sp-70, American Concrete Institute, Detroit, MI, pp. 983-96. 

MAJOR PRODUCT APPLICATIONS cosmetics, pharmaceuticals, mbber, tire, paint, coatings, paper, agriculture, floor covering, crack fillers, primers, films, wire and cable, electrical accessories, can sealants, roofing membranes, syringes, coated fabrics, tennis balls, urethane sealants, foam, gaskets, footwear... 

Urethane sealants were first used in in-plant assembly applications. In 1960 the... 

Improved bonding of polysulfide or urethane sealants to metal substrates or glass. 

Lord 7610 A one part, urethane sealant/adhesive for composites application, offering a working time... 

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