Continuous process for preparing a polyurethane latex

Abstract

A polyurethane/urea/thiourea latex having a narrow molecular weight polydispersity and sub-micron particle size can be prepared by first preparing a high internal phase ratio (HIPR) emulsion of a polyurethane/urea/thiourea prepolymer, then contacting the emulsion with a chain-extending reagent under such conditions to form the polymer latex.

What is claimed is:  
     
         1 . A composition comprising a polyurethane latex having a mean volume average particle size of not greater than about 1 micron and a solids content of at least 45 percent by weight, wherein the polyurethane latex contains the following units:  
       
         
           
           
               
               
           
         
       
       where R and R′ are each aromatic.  
     
     
         2 . The composition of  claim 1 , wherein the polyurethane latex contains units formed from 4,4′-diisocyanatodiphenylmethane or 2,4′-diisocyanatodiphenylmethane or a combination thereof.  
     
     
         3 . The composition of  claim 1 , wherein the polyurethane latex has a solids content of not less than 50 percent by weight based on the total weight of the latex.  
     
     
         4 . The composition of  claim 3 , wherein the latex has a solids content of not less than 55 percent by weight based on the total weight of the latex and has a volume average particle size of not greater than 0.5 micron and a polydispersity of not greater than 1.5.  
     
     
         5 . The composition of  claim 1 , wherein the polyurethane latex has a mean volume average particle size of not greater than about 0.5 micron.