Researchers investigatred various inhibitors that retard the formatino of allophanate linkages during the synthesis of acid, benxoyl chloride, ethyl cyanoacetate, and diethyl malonate. Various polyurethanes were formed by reacting phenyl isocyanate with N-phenylurethane in DMF and by reacting bis(4-isocyanatophenyl) methane with a diol mixture of poyethylene adipate and ethylene glycol in DMF. An examination of the raction rate constants revealed that phosphoric acid was the most effective inhibitor: increasing the concentration of phosphoric acid past 60 parts per million significantly retarded the formation of allophanate linkages during polyurethane synthesis. 8 refs.