Compounds of formula I ##STR1## wherein R.sub.1, R.sub.2, R. sub.3 and R.sub.4 are each 2-ethylhexyl or are independently higher alkyl, or R.sub. 1 and R.sub.2 are independently hydrogen or methyl, and R.sub. 3 and R.sub. 4 are independently higher alkyl are effective processing stabilizers for polymers processed at elevated temperatures by preventing polymer degradation and providing resistance to discoloration. The compounds of formula I also exhibit superior hydrolytic stability and resist moisture pickup on storage.
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