ETHYLENE-CO-VINYL ALCOHOL BLENDS

The presence of the aliphatic hydroxyl group in poly(ethylene-co-vinyl alcohol) (EVOH) suggests that these copolymers have the potential for forming miscible blends with a variety of polymers containing complementary functional groups such as esters, (meth)acrylates, acetoxys, pyridines, etc. There is a paucity of examples of miscible EVOH blends in the literature, however. Hydrogen bonding, which is very complicated in EVOH copolymers and involves an extraordinary variety of inter- and intramolecular species, plays an important role in the phase behavior of EVOH blends. We have applied an association model to this problem and arrived at the following important conclusion. Miscible EVOH blends with polymers containing ester or acetoxy groups do exist, but they have lower critical solution temperatures below normal processing temperatures (< 200-degrees-C). This is primarily a consequence of the fact that EVOH copolymers are strongly self-associated, while the interassociation of the hydroxyl groups of EVOH with the carbonyl groups of the complementary polymers is comparatively weak.