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

Abstract

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 (χc), and glass-transition temperature (T g) compared to less regular structures. EVOH(44) demonstrated the highest T m but lower χc 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).