example in the formula str3 r 39 is a carbonyl group or r and r 39 are the same or different hydrocarbon moieties which may be acyclic aliphatic cyclic or bicyclic or aromatic n is an integer of 0 or 1 x and y are integers of from 0 to 2 providing that when n is 0 y is 0 and when r 39 is a carbonyl group y is 0 representative substituents include phenylene naphthalene anthrylene cyclobutylene cyclopentylene cycloheptylene cyclohexylene cyclooctylene octylene hexylene heptylene butylene and the like with preferably two carboxylic acid groups per molecule i e per r group preferably positioned ortho to the carbonyl groups preferably r and r 39 have from 3 to 6 carbon atoms excluding the pendant carboxylic acid groups and x y 2 to 4 or r 39 is a carbonyl group and x is 2 representative examples of hydrophilic materials are exemplified by the following structures str4 the hydrophilic polymers are made by conventional means such as by mixing equimolar quantities of an acid dianhydride with an acid hydrazide or diamine and the like in a suitable solvent such as anhydrous n methyl pyrrolidone or dimethyl acetamide at room temperature for about 18 hours under an inert atmosphere such as a nitrogen atomosphere the solution can then be sprayed draw bar coated or the like onto the substrate and heated for about 1 2 hour at 50 u00b0 c to evaporate the solvent cure the polymer and bond it to the substrate if desired fillers and other additives can be mixed with the hydrophilic polymers to provide strength or additional hydrophilicity such as zinc oxide carbon black titanium dioxide and the like conventional thermal means can.