Isonate M 340 Isocyanate Dow Chemical PU - Prepolymers >> Isocyanate >> MDI based MDI prepolymer ISONATE* M 340 is a liquid derivative of 4,4'-diphenylmethane diisocyanate having a functionality(1) of 2.1 and an isocyanate content of 26.3%. ISONATE M 340 has been specifically designed for use in elastomeric applications. Since it has a linear structure, elastomers and elastoplastics having a high level of performance can be prepared from it. MDI prepolymer. Liquid derivative of 4,4'-diphenylmethane diisocyanate. Used in elastomeric applications.