Regio- and Stereoregular EVOH Copolymers from ROMP as Designer Barrier Materials

This work aimed to decrease the water permeability (P_H2O) while simultaneously maintaining low oxygen permeability (P_O2) in ethylene vinyl alcohol (EVOH)-based copolymers by introducing high levels of backbone regioregularity and stereoregularity. Both regioregular atactic and isotactic EVOH samples with 75 mol % ethylene were prepared by a ring-opening metathesis polymerization (ROMP)-hydrogenation-deprotection approach and then compared to commercial EVOH(44) (containing 44 mol % ethylene) as a low P_O2 standard with poor water barrier characteristics (i.e., high P_H2O). The high levels of regioregularity and stereoregularity in these copolymers increased the melting temperature (T_m), degree of crystallinity (χ_c), and glass-transition temperature (T_g) compared to less regular structures. EVOH(44) demonstrated the highest T_m but lower χ_c and T_g values as compared to that of the isotactic polymer. Wide-angle X-ray scattering showed that semicrystalline EVOH(44) exhibited a monoclinic structure characteristic of commercial materials, while ROMP-derived polymers displayed an intermediate structure between monoclinic and orthorhombic. Tensile testing showed that isotacticity resulted in brittle mechanical behavior, while the atactic and commercial EVOH(44) samples had higher tensile toughness values. Although EVOH(44) had the lowest P_O2 of the samples explored, the atactic and tough ROMP-derived polymer approached this value of P_O2 while having a P_H2O over 3 times lower than that of commercial EVOH(44).