Isocyanates millable polyurethanes

Millable polyurethane elastomers are elastomers to which the conventional techniques of mill compounding and vulcanization can be applied. In this approach, stable (hydroxyl-terminated) polymers are prepared by the reaction of linear polyesters (commonly adipates) or polyethers (commonly poly(oxytetramethylene) glycol) with diisOcyanates. These polymers are rubber-like gums which may be compounded on two-roll mills with other ingredients. Vulcanization may be effected by several types of reagents, but isocyanates, sulphur systems and peroxides are the most widely used. 

Yeganeh, H., Mehdizadeh, M.R., 2003. Synthesis and properties of isocyanate curable millable polyurethane elastomers based on castw oil as a renewable resource polyol. Eur. Polym. J. 40, 1233-1238. 

Polyurethanes similar to those utilized as millable elastomers (Section 14.6.2) may be used as adhesives provided the molecular weight is low enough to permit solubility in appropriate organic solvents. Isocyanates are generally the preferred cross-linking agents for these adhesives since they are effective at low temperatures. Such adhesives give flexible bonds and are used in the shoe industry. 

Method D appears to be possibly the most important type of isocyanate-based adhesive system. It is similar to Method B in that a preformed, fully reacted, high molecular weight polymer is employed as a vehicle in the adhesive formulation. The strength of the vehicle holds adherend members in exact position after assembly until the full bond has formed. Method D differs from Method B in that its vehicle polymer is a polyurethane. A further difference is that the inherent adhesive character and strength of the polyurethane vehicle frequently enables its use without added di- or poiyisocyanate. This strength may be realized in essentially amorphous compositions such as the thermoplastic polyurethane elastomers or millable gums. Or it may be achieved with crystallizing urethane adhesive polymers. 

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