only two symmetrical stabilizers in a polyolefin or copolymer thereof , provide thermooxidative or antioxidative stability . one is an arylphosphite or arylfluorophosphite ; the other is a monomolecular tri - substituted triazine in which each of three chlorine atoms on a trihalo - s - triazine is substituted with a piperazinone in which the n atom in the 4 - position is alkylated . only a trace amount of phosphite , at least 0 . 01 phr but less than 0 . 1 phr , is used so that the ratio of the piperazinone - substituted stabilizer to ester is greater than 1 ; additional phosphite has no noticeable effect . the trace amount of phosphite has a surprising booster effect , giving the stabilized composition excellent to stability . articles thermoformed from the stabilized polyolefin or copolymer thereof may be used under the hood or the dash of a vehicle , and , in containers for packaging goods , all of which articles are subject to to degradation even if they are not subject to ultraviolet light degradation .