Process for preparing oxidatively-stable polymers by reaction with antioxidant in the presence of free radical

A process for preparing an oxidatively stable polymer which comprises reacting the polymer with an antioxidant of the formula:

• ##STR16## in which R.sub.1 and R.sub.2 each independently represents a hydrogen atom or a tertiary alkyl radical such that at least one represents a tertiary alkyl radical and R.sub.3 represents a hydrogen atom or an alkyl, hydroxy, hydroxyalkyl, alkoxyalkyl or mercaptoalkyl radical, said R radicals optionally being substituted by aromatic phenolic or aromatic amine groups, in the presence of a free radical with the proviso that when the free radical is produced by a free radical generator, said generator produces free radicals at a temperature below about 120.degree. C.