Room Temperature Morphologies of Precise Acid- and Ion-Containing Polyethylenes

The room temperature morphologies of twelve precise copolymers based on polyethylene (PE) were studied by solid-state C-13 NMR, DSC, and X-ray scattering. These copolymers feature carboxylic acid, phosphonic acid or 1-methylimidazolium bromide pendants on exactly every 9th, 15th or 21st carbon atom along the linear PE chain. The morphologies were categorized by the arrangement of the acid or ionic aggregates into liquid-like, layered, or cubic morphologies. The liquid-like morphology is characterized by an amorphous PE matrix and liquid-like packing of the aggregates, wherein the interaggregate spacing increases with l. both the PE segment length and the pendant size. The layered morphologies typically have a semicrystalline PE matrix and upon stretching become highly anisotropic. Notably, the orientation of the aggregates and the PE crystallites relative to the stretch direction depends on whether the morphology is dominated by PE crystallization, as found for acrylic acid (AA) and phosphonic acid (PA) copolymers, or by the strong ionic aggregates, as found for the 1-methylimidazolium bromide (ImBr) copolymers. Cubic morphologies in these precise copolymers require geminal substitution, PA pendants, and sufficiently long PE segments to allow the aggregates to order. These precise copolymers provide an unprecedented array of morphologies that enable correlations between chemical structure and nanoscale morphologies.