for a suitable period of time so that the majority of the charged diphenylamine is alkylated thereafter the reaction temperature is reduced to a second temperature in range of about 140 u00b0 c to about 160 u00b0 c preferably in the range of about 145 u00b0 c to about 155 u00b0 c and more preferably in the range of about 150 u00b0 c to about 155 u00b0 c the second temperature is maintained for a period of time such that the total composition contains less than about 1 0 weight percent of unreacted diphenylamine and more preferably less than about 0 8 weight percent preferably from less than about 0 8 to about 0 2 weight percent in the product the reaction pressure can range up to about 250 psi or higher preferably below about 250 psi and more preferably in the range of about 25 to 100 psi inert gas such as nitrogen can be used to minimize oxidation of products during reaction but mostly to allow operation at higher temperatures with the lower boiling oligomers a nitrogen or other inert gas atmosphere in contrast to air suppresses the formation of products that deactivate the clay catalyst other benefits of nitrogen pressure include higher rates of reaction shorter.