Polyurethane isocyanate-terminated

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

It is common in acrylic structural adhesives to use oligomers that have a desirable backbone and are terminated with free-radical-polymerizable bonds. A variety of isocyanate-terminated polyurethanes can be adapted to use in acrylic structural adhesives by reacting the terminal isocyanates with a hydroxy functional acrylic monomer such as 2-hydroxyethyl methacrylate.76,92 93... 

Hawkins, J. M., Epoxy Resin Adhesive Compositions Containing an Isocyanate Terminated Polyurethane Prepolymer and a Chain Extender, U.S. Patent No. 3,636,133, 1972. 

The laminating adhesive for Samples 1-3 was a 100 25 mix of an isocyanate terminated polyurethane prepolymer based upon polypropylene glycol and MDI (amount of free monomer approximately 25%) and a tri-functional polypropylene glycol with a molecular weight of approximately 450. 

This prepolymer (Scheme 1.10) is then reacted with a chain-extender diol or diamine to give the final polyurethane or polyurethane-polyurea block copolymer, respectively. The diversity in properties that the final urethane block copolymers exhibit is governed by the nature of the three building blocks the diol-terminated polyester, the di-isocyanate-terminated polyurethane and the chain extender (Hepburn, 1982). As shown in Figure 1.17, these form flexible blocks (from the polyester) that undergo phase segregation as structures of size 1000-2000 nm. 

Using this technique, a large variety of polyurethanes have been prepared from different vegetable oils. Natural polyols like castor oil (generally trifunctional) are directly reacted with diisocyanates to obtain branched polyurethanes, although it is difficult to control the reactivity. However, bifunctional castor oil can be polymerised with diisocyanates in the presence of suitable chain extenders and catalysts to produce polyurethanes in a more controlled manner (Fig. 6.4). A castor oil polyol-based polyurethane network can also be prepared from epoxy terminated polyurethane pre-polymer with 1,6-hexamethylene diamine. Epoxy terminated pre-polymer is obtained by the reaction of glycidol and isocyanate terminated polyurethane pre-polymer of castor oil polyol, poly(ethylene glycol) (PEG) and 1,6-hexamethylene diisocyanate. ... 

Preparation Polyurethane (PU), The isocyanate-terminated polyurethane prepolymer was prepared by reacting two equivalent weights of 4,4 -diphenylmethane diisocyanate (MDI) with one equivalent weight of poly(caprolactone) glycol (Niax D-560) at 60 C. The prepolymer was stored under vacuum (for not more than two days) because of its susceptibility to... 

An isocyanate-terminated polyurethane, derived from TDI and polypropylene glycol with MW = 600, shows N—H bands at 1470 and 2040 nm. The 2040 nm band increases on heat curing [16]. NIR can be used to monitor the ratio of polyol or polyester being reacted with isocyanate. A substantial reduction in scrap rate occurs when precise ratios of polyol and isocyanate are known by the molding operator. 

Polyurethane reactive hot melt adhesives (PURhma) consist of an isocyanate-terminated polyurethane or high molecular weight hydroxyl-terminated polyurethane which is solid at ambient temperature, but which melts at low temperature. They bond through the physical process of rapid solidification from the melt as well as through chemical reaction with ambient moisture. As a result of... 

Another approach is to first prepare an isocyanate-terminated polyurethane in acetone. This is then chain extended with a sulfonate substituted diamine. The acetone solution is diluted with water, and then the acetone is removed by distillation leaving an aqueous polyurethane dispersion stabilized by charge repulsion of sulfonate groups. 

For example, one-component isocyanate-terminated polyurethane prepolymers in solution are cured by reaction with moisture in 2-24 h, depending on bond thickness. Carbon... 

---