Urethanes from Stable Prepolymers

The use of Nitrosan as blowing agent has one or two disadvantages. Nitrosan is relatively unstable and considerable caution is required when handling. When machine processing, the Nitrosan has to be metered as a 

The technique of using water as the blowing agent also has limitations. In this case the water and MOCA are competing for the available isocyanate in the prepolymer, making the ratio of water to MOCA used very critical. Furthermore, the gas evolution and chain extension proceed simultaneously and a delicate balance between this gas formation and the chemical and physical changes in the polymer has to be maintained to obtain satisfactory results. 

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