tight matrix the following example 2 illustrates the preparation of a preferred polyether polyurethane for use in an amount up to 20 by weight based upon the total weight of the binder material of the present compositions i e in combination with at least 80 by weight of the water soluble acrylic polymer 0021 material parts by wt mol wt moles equivalents ratio polytetra 100 2000 05 1 1 0 methylene ether isophorone 25 25 202 125 25 2 5 diisocyanate dimethyol 3 7 148 025 05 5 propionic acid dmpa isophorone 6 57 146 045 09 9 diiamine triethylamine 2 52 101 025 025 25 tea the polyurethane in example 2 is technically a polyurea since diamines are used to chain extend the urethane prepolymer react with the diisocyanates the dmpa allows the urethane to go into water solution amines are preferred to react with aliphatic diisocyanates in commercial applications as they give good film tensile properties whereas the use of diols typical in aromatic urethane usage would not isophorone diamine is used as the chain extension agent since an aliphatic diisocyanate s must be used when diamines are used as the chain extending agents polyethers such as polytetramethylene oxide are used because they will not hydrolyze or break down in the presence of water or moisture this increases the washability compared to polyester based polyurethanes also they are resistant to fungus and mildew as discussed above the formed aqueous polyurethane comprises a polyurea formed by the reaction of the diamine which functions as a chain extending agent with the isophorone diisocyanate s the dimethylol propionic acid assists in the curing or crosslinking of the.