Deformation-induced morphology evolution of precise polyethylene ionomers

Abstract

The morphology evolution during deformation was characterized for a series of lithium neutralized acrylic acid containing linear polyethylenes (PEs). In situ X-ray scattering measurements simultaneously captured the changes in the inter-ionic aggregate peak and amorphous halo during uniaxial elongation. The effects of spacer length between pendant acid groups on the linear PE backbone, fraction of neutralized acid groups, and temperature were examined. This study indicates that the neutralization of the acid-functionalized precise polymers with metal salts significantly increases the melting and glass transition temperatures and improves mechanical properties, while the accessible morphologies remain controlled by the underlying polymer structure. During deformation above the thermal transitions, an anisotropic layered morphology similar to that found in the acid forms with 15 and 21 carbon spacers was observed in the precise ionomers with 9, 15, and 21 carbon spacers. Precise polymers with the highest acid and ionic content corresponding to a 9-carbon spacer have the highest ultimate tensile strength in the melt state due to persistent ionic aggregates. At elevated temperatures strain hardening was observed when significant chain orientation occurred corresponding to an anisotropic layered morphology, indicating some chain mobility through facile aggregate exchange.