Polyurethane, moisture curing prepolymers

Polyurethane 3651 is a moisture-curing prepolymer at 60% solids in xylol and Cellosolve acetate. 

In formulating polyurethane/urea systems using ultra-low monol PPG polyols, it was found that polyol MWD has a major effect on polymer properties. A broadened MWD is required to achieve a property profile similar to a PTMEG-based system. The MW-distribution effect is illustrated using TDI prepolymers cured with MBOCA, TDI moisture-cured prepolymers and aqueous polyurethane/urea dispersion coatings. 

Ready for application to wood or concrete floors at 40% solids. Polyurethane 3651 is a moisture-curing prepolymer at 60% solids in xylol and Cellosolve acetate and is made by Cargill Inc., USA. 

Fig, 17. (a) Isocyanate-terminated polyurethane prepolymer synthesis, (b) Moisture cure of isocyanate-terminated polyurethane prepolymers, (c) Side reactions of isocyanate-terminated polyurethane prepolymers. 

Example 11. One-Component, Moisture-Cure Polyurethane Sealant. This example is of a low-hardness, high-elongation, moisture-curable polyurethane sealant. The material is based on a low-%NCO prepolymer made from 4,4 -MDI and a low-unsaturation (low-monol-content) Acclaim polyol from Bayer. It is adapted from (a) J. Lear et al., Adhesives Age, February 1999, pp. 18-23 and (b) B. Lawrey, et al., presented at UTECH 2000, The Hague, The Netherlands, March 30, 2000, Crain Communications London, 2000. 

Polyurethane reactive hot melts are 100% solid, hot-melt thermoplastic prepolymers that moisture cure slowly after application. Conventional hot melts are known for their quick setting, excellent green strength, ease of application, and low toxicity. Their primary limitation is low heat resistance (at elevated temperatures, the adhesive will soften and flow) and poor adhesion to some substrates, due to insufficient wetting. The use of a polyurethane prepolymer with low levels of free isocyanates as a hot melt offers distinct... 

Chem. Descrip. Polyurethane prepolymer Uses Prepolymer for formulating moisture-cure primer systems for industrial coatings... 

To determine if the polyol MWD effect can be seen in other polyurethane/urea systems, a moisture-cured film was prepared using a 2 1 prepolymer based on 2,4-TDI and PPG-1000 and this was compared with one based on 4000-MW PPG blended with DEG to a MW of 1000. Table 9.19 shows the mechanical properties of the films in bold type. The dramatic increases in 100% modulus (1.3 to 3.6 MPa), tensile strength (14 to 35 MPa) and tear strength (18 to 58 IcN/m) obtained by broadening the MWD of the polyol can... 

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. 

Polyurethane sealant formulations use TDI or MDI prepolymers made from polyether polyols. The sealants contain 30—50% of the prepolymer the remainder consists of pigments, fiUers, plastici2ers, adhesion promoters, and other additives. The curing of the sealant is conducted with atmospheric moisture. One-component windshield sealants utili2e diethyl malonate-blocked MDI prepolymers (46). Several polyurethane hybrid systems, containing epoxies, siUcones, or polysulfide, are also used. 

Single component systems rely in most cases for the cure to take place by the reaction of moisture in the air with the prepolymer to form a solid polymer. Carbon dioxide gas is given off during this reaction and either escapes into the air or is trapped by fillers in the system. These systems are used to make waterproof barriers and single pack polyurethane paints. 

Novel, toughened one-component epoxy structural adhesives based on epoxy-terminated polyurethane prepolymer incorporating an oxolidone structure were developed to provide improved toughness, fracture resistance and adhesive properties with good chemical and moisture resistance.21 The hybrid resin cures with a standard latent curing agent/accelerator. 

First-generation solventless polyurethane adhesives are one-component isocyanate terminated prepolymers formed by the reaction of MDI (4,4 methylene bis (phenyl isocyanate)), or other isocyanates with polyether and/ or polyester polyols. One-component 100% solids adhesives rely on moisture from the air or substrates or from induced moisture misting during the converting process, to cure the adhesive via an isocyanate/water reaction and subsequent polyurea-polyurethane polymer formation. Typically the high viscosity of the adhesive is such as to require adhesive delivery equipment and application rollers heated from 65-80 °C for use. They have a high level... 

Conventional (1-component) polyurethane spray foams are cured by a reaction of NCO-prepolymers with moisture to generate an urea unit and CO2 [1]. The latter serves as a propellant or... 

Chemically reactive polyurethanes include both one- and two-component systems. One-component systems are usually based on a polyether polyol treated with a polyisocyanate to give an isocyanate-terminated polymer. A one-component system cures when exposed to moisture at room temperature. One-component polyurethane hot-melt adhesives are also cured by moisture after application. Two-component systems result from the reaction of low molecular mass polyols and isocyanates or from isocyanate-terminated prepolymers with either polyols or polyamines. Two-component systems cure at room and/or elevated temperatures. 

Hydroxyl-containing silicon material with the hydroxyl groups attached directly to a silicon atom are combined together to react to form silanol-functionalised urethane prepolymers that can cure at ambient temperatures in the presence of moisture to form polysiloxane polyurethanes. For instance, physical blends of a polypropyleneoxide polyol intermediates and an organic-silicone block copolymer-based polyol intermediates have been prepared to improve elongation and reduced... 

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