Polymers are seldom used in the pure state; various additives may be present, of which one category includes a second polymer. This paper presents a review of the effect on the degradation properties of a polymer of the presence of a second polymer in its environment. The approach which has been used in discussing the degradation of polymer blends is to consider, in turn, for poly(methyl methacrylate), poly(vinyl chloride) and polystyrene, the effect on degradation due to the presence of various second polymers. Polymer blends are heterogeneous systems and the observed effects on degradation behavior clearly reflect the two-phase character. Most of the observed interaction processes involve reaction of a product of degradation of one polymer with the other polymer, as a result of the diffusion of a mobile small molecule or radical out of the phase in which it is formed into the other phase. Direct reactions between dissimilar macromolecules have not been observed. The interaction processes result in some cases in destabilization; in other cases the thermal stability is improved in the blend.
McNeill, I. C. (1977). THERMAL DEGRADATION OF POLYMER BLENDS. Dev in Polym Degradation - 1, 171–204.