u00b0 c for specified periods of time the pressure vessels were then allowed to cool to room temperature at which the polymer content methanol precipitation and viscosities using cannon fenske viscometers of the samples were measured py gas oil viscosity was measured at 20 u00b0 c after being heated at 150 u00b0 c for 7 5 hours three trials were performed one blank the second with 1000 ppm phenylenediamine and the third according to the inventive method including 1000 ppm of the quinone methide of formula ii above table 1 below demonstrates that the viscosity of the py gas oil after treatment with the inventive quinone methide was 43 6 less than after treatment with phenylenediamine alone and 55 1 less than the blank after the py gas oil was subjected to conditions simulating those in an oil quench tower py gas oil viscosity at 23 u00b0 c was measured after being heated at 144 u00b0 c for six hours with the amounts of treatment listed in table 2 this demonstrates that up to a concentration of 2000 ppm a greater concentration of the inventive quinone methide treatment provides an enhanced inhibition of viscosity increase the polymer content in py gas oil samples was measured by methanol precipitation after heating at 150 u00b0 c for 7 5 hours three trials were performed one blank the second with 1000 ppm phenylenediamine and the third according to the inventive method including 1000 ppm of the quinone methide of formula ii above the results in table 3 indicate that the polymer content of the py gas oil samples after treatment with.