Commercial Preparation of Prepolymers

Hepburn (1982) gives two main routes for the preparation of polyurethanes based on the relative activities of the various ingredients  

Chain extension/cross-linking to complete production of polyurethane One-Shot Systems 

The unstable prepolymers are typified by the Bayer Vulkalon polyurethane. Vulkalon is generally made by reacting naphthalene diisocyanate (NDI) and hydroxyl terminated polyesters to form a prepolymer. The reactivity of the 

The best physical properties are obtained with polyethylene adipate as the backbone. After the manufacture of the prepolymer with the polyethylene adipate and NDI, the polyurethane was completed with the addition of BDO. The use of diamines gave too fast a reaction for successful processing. Water and glycols also were used for cross-linking. Glycols do not give the C02 gas the water chain extension does. 

To improve the low temperature properties, a different backbone needs to be used. A mixture of polyethylene and polypropylene adipates has been found to be suitable. The physical properties are not as good as with the single polyol. 

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