MDI-based polyurethane prepolymer with low monomeric MDI content

Abstract

An MDI/polypropylene polyether prepolymer composition consisting essentially of at least 80 wt % perfect prepolymers and less than 2 wt % free MDI monomer suitable for use in polyurethane adhesive compositions optionally also comprising a curative for isocyanate groups.

We claim:  
     
         1 . A prepolymer composition comprising the reaction product of 4,4′-diphenylmethane diisocyanate with a polyol composition comprising a propylene oxide based polyether polyol and consisting essentially of at least 80 wt % perfect prepolymers and less than 2 wt % free MDI monomer.  
     
     
         2 . The prepolymer composition of  claim 1  in which the 4,4′-diphenylmethane diisocyanate comprises isomeric mixtures of MDI and/or polymeric MDI.  
     
     
         3 . The prepolymer composition of  claim 1  in which the 4,4′-diphenylmethane diisocyanate comprises an isomeric mixture of MDI containing 30-98 wt % of 4,4′ isomer, 2-70 wt % of the 2,4′ isomer, and 0-5 wt % of the 2,2′ isomer (with the wt % totaling 100%); and/or polymethylene poly(phenylisocyanate) having an average isocyanate functionality of 2.1 to 3.5, isocyanate group content of 18.0 to about 33.6, and containing about 30 to 96 wt % monomeric 4,4′ MDI, about 2-70 wt % monomeric 2,4′ MDI, and less than 5 wt % monomeric 2,2′ MDI, and from 2-60 wt % higher ring homologues of the MDI series (with the wt % totaling 100%)  
     
     
         4 . The prepolymer composition of  claim 1  in which the propylene oxide based polyether polyol is a polypropylene polyether polyol with functionality of two or greater and an average equivalent weight between 100 and 3000.  
     
     
         5 . The prepolymer composition of  claim 1  in which the propylene oxide based polyether polyol is an ethylene oxide capped polypropylene polyether polyol.  
     
     
         6 . The prepolymer composition of  claim 1  in which 0 to 60 wt % of the polyol composition comprises a di- or multi-functional alkylene ether polyol, a polyester polyol, a polyester polyol from polycaprolactones or a hydroxyl terminated polybutadienes  
     
     
         7 . The prepolymer composition of  claim 1  consisting essentially of at least 90 wt % perfect prepolymers.  
     
     
         8 . The prepolymer composition of  claim 1  consisting essentially of less than 1 wt % free MDI monomer.  
     
     
         9 . The prepolymer composition of  claim 1  containing a free prepolymer NCO functionality ranging from 0.2 to 15 wt %.  
     
     
         10 . The prepolymer composition of  claim 1  in which the polyol composition has an average Mn ranging from about 400 to 16,000.  
     
     
         11 . A prepolymer composition comprising the reaction product of 4,4′-diphenylmethane diisocyanate with a polyol composition comprising a polypropylene polyether polyol with functionality of two or greater and an average equivalent weight between 100 and 8000 and consisting essentially of at least 90 wt % perfect prepolymers, less than 2 wt % free MDI monomer and a free prepolymer NCO functionality ranging from 0.2 to 15 wt %.  
     
     
         12 . The prepolymer composition of  claim 11  in which the 4,4′-diphenylmethane diisocyanate comprises an isomeric mixture of MDI containing 30-98 wt % of 4,4′ isomer, 2-70 wt % of the 2,4′ isomer, and 0-5 wt % of the 2,2′ isomer (with the wt % totaling 100%); and/or polymethylene poly(phenylisocyanate) having an average isocyanate functionality of 2.1 to 3.5, isocyanate group content of 18.0 to about 33.6, and containing about 30 to 96 wt % monomeric 4,4′ MDI, about 2-70 wt % monomeric 2,4′ MDI, and less than 5 wt % monomeric 2,2′ MDI, and from 2- 60 wt % higher ring homologues of the MDI series (with the wt % totaling 100%)  
     
     
         13 . The prepolymer composition of  claim 11  in which the propylene oxide based polyether polyol is an ethylene oxide capped polypropylene polyether polyol.  
     
     
         14 . The prepolymer composition of  claim 11  in which 0 to 60 wt % of the polyol composition comprises a di- or multi-functional alkylene ether polyol, a polyester polyol, a polyester polyol from polycarbonate or a hydroxyl terminated polybutadiene.  
     
     
         15 . The prepolymer composition of  claim 14  consisting essentially of less than 0.5 wt % free MDI monomer and containing a free prepolymer NCO functionality ranging from 0.5 to 8 wt %.  
     
     
         16 . The prepolymer composition of  claim 15  in which the polyol composition has an average Mn ranging from about 400 to 16,000.  
     
     
         17 . In a polyurethane adhesive composition comprising a polyurethane prepolymer composition and, optionally, an isocyanate-reactive curative, the improvement which comprises the prepolymer composition of  claim 1 .  
     
     
         18 . In a polyurethane adhesive composition comprising a polyurethane prepolymer composition and, optionally, an isocyanate-reactive curative, the improvement which comprises the prepolymer composition of  claim 11.