an oxo - piperazinyl triazine with three piperazinone substituents , each of which has an alkylated n 4 atom , used in an amount no more than 0 . 2 phr , and without any secondary stabilizer , and in particular , without any hindered phenol antioxidant , or phosphorous acid ester , simultaneously provides thermooxidative stability and stability against degradation by uv light along with acceptable melt processability . further , the virgin mpip - t allows uninterrupted operation of a die or mold while maintaining the surfaces of the cavities essentially contaminant - free ; and , excellent ao stabilization which is equivalent to that obtained with a premier hindered phenol ao , and superior to that obtained with the premier oligomeric piperidinyl - triazine compound , when each stabilizer is used in the same amounts by weight in a thermoplastic synthetic resinous substrate .