Prepolymer safety

Most general-purpose release agents have been developed for this market in part because of their low toxicity and chemical inertness and do not usually present health and safety problems. Some of the solvent dispersions require appropriate care in handling volatile solvents, and many supphers are offering water-based alternatives. Some of the sohds, particularly finely divided hydrophobic sohds, can also present inhalation problems. Some of the metallic soaps are toxic, although there is a trend away from the heavier, more toxic metals such as lead. The reactive type of release coating with monomers, prepolymers, and catalysts often presents specific handling difficulties. The potential user with health and safety questions is advised to consult the manufacturer directly. 

On completion of the reaction, the material may be carefully degassed to remove any entrapped gasses and unreacted diisocyanate. Care must be taken to prevent foaming. Applying vacuum to the glassware does create the potential for it to implode. Suitable safety precautions must be taken. Table 3.2 indicates some typical time/temperature reaction conditions for some simple prepolymers. 

Castable Polyurethane Elastomers explains the production process of polyurethane components from both the theoretical and practical points of view. It describes the underlying concepts for the raw material supplier recommendations and explains how to achieve application-specific properties in polyurethane. The book explains the production of prepolymers with special focus on health and safety issues. It presents the different types of methods available on both the micro and macro levels and explains the rationale behind choosing the system needed to create a cost-effective, application-specific product. 

In the past, fabricators would commonly mix directly a preselected polyol with an isocyanate and chain extender in what was called a one shot method. However, today, it is far more likely that the fabricator will have the supplier prereact the polyol with a designated diisocyanate to form what is called an isocyanate-terminated prepolymer. The fabricator would rather work with these isocyanate-terminated prepolymers because there should be less chance of worker exposure to free isocyanates in the product fabrication. There are significant worker safety concerns with exposure to isocyanates. 

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