modified polystyrenes are described which are catalysts for the conversion of organic isocyanates to the corresponding carbodiimides . the modified polystyrenes are characterized by the presence of recurring units of the formula : ## str1 ## r 1 and r 2 are hydrocarbyl which is free of substituents reactive with isocyanate groups , r 3 is hydrogen , chloro or methyl , r 4 is hydrogen or methyl , and n is 0 or 1 . the use of the above polymers to catalyze the formation of carbodiimides from organic isocyanates is also disclosed .