Isonate M 342 Isocyanate Dow Chemical PU - Prepolymers >> Isocyanate >> MDI based MDI prepolymer ISONATE* M 342 is a liquid derivative of 4,4'-diphenylmethane diisocyanate having a functionality(1) of 2.0 and an isocyanate content of 23.3%. ISONATE M 342 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.