We report the detailed characterization of strictly linear ethylene-co-acrylic acid (EAA) copolymers synthesized via two modes of olefin metathesis polymerization, where control of the polymer microstructure leads to the generation of unique polymer morphologies based on distribution of carboxylic acid moieties along the polymer backbone. Acyclic diene metathesis (ADMET) was used to prepare three high molecular weight, high strength EAA materials bearing pendant carboxylic acid groups along the copolymer backbone precisely placed every 9th, 15th, and 21st carbon, and ring-opening metathesis polymerization (ROMP) was used to create EAA materials of equimolar acid concentrations with irregularly distributed pendant groups along the linear copolymer backbone. Primary structure characterization using FT-IR and NMR techniques are discussed as well as secondary structure analysis via DSC and X-ray scattering. Thermal analysis indicates significant effects of functional group placement on melting temperatures and enthalpies illustrating the importance of ethylene sequence lengths and distributions on polymer crystallization. X-ray scattering reveals broad scattering peaks with evidence of orthorhombic polyethylene-like crystallization in all irregular copolymers except the most highly functionalized, fully amorphous material. The precise carboxylic acid copolymers have X-ray scattering peaks indicative of acid−acid spacing along all-trans polyethylene segments of the polymer chain. Only the regularly functionalized EAA copolymer with the lowest acid content is semicrystalline with evidence of orthorhombic polyethylene-like crystallization, while higher concentrations of acids groups lead to amorphous materials. Drawing the semicrystalline ADMET acid copolymer produces an anisotropic morphology, indicating that the acid−acid spacing is parallel to the polyethylene chain axis.

The morphology of a series of linear poly(ethylene-co-acrylic acid) zinc-neutralized ionomers with either precisely or randomly spaced acid groups was investigated using X-ray scattering, differential scanning calorimetry (DSC), and scanning transmission electron microscopy (STEM). Scattering from semicrystalline, precise ionomers has contributions from acid layers associated with the crystallites and ionic aggregates dispersed in the amorphous phase. The precisely controlled acid spacing in these ionomers reduces the polydispersity in the aggregate correlation length and yields more intense, well-defined scattering peaks. Remarkably, the ionic aggregates in an amorphous, precise ionomer with 22 mol % acid and 66% neutralization adopt a cubic lattice; this is the first report of ionic aggregate self-assembly onto a lattice in an ionomer with an all-carbon backbone. Aggregate size is insensitive to acid content or neutralization level. As the acid content increases from 9.5 to 22 mol % at approximately 75% neutralization, the number density of aggregates increases by approximately 5 times, suggesting that the ionic aggregates become less ionic with increasing acid content.

This paper reports the first quantitative reconciliation of imaging and scattering data for poly(styreneran-styrenesulfonate) (P(S-SS x )) ionomers. We examined the morphology of solvent-cast and spin-cast P(S-SS 0.019 )-M ionomers using the combination of scanning transmission electron microscopy (STEM) and X-ray scattering, where the scattering data were fit with a liquidlike hard-sphere model. Both the ionic aggregate sizes (R 1 ) and the sample volume per ionic aggregate (V P ) as measured by both techniques were in good agreement. In addition, STEM found that P(S-SS 0.019 ) ionomers prepared by spin-casting exhibit nanometer spherical ionic aggregates that are indistinguishable in size, shape, and spatial distribution from the bulk solvent-cast ionomers. Six P(S-SS 0.019 )-M ionomers fully neutralized with various cations have ionic aggregate compositions that are predominately ionic, and the ionic aggregate radius (R 1 ) increases as the cation radii increases. Finally, the influence of copolymer type was studied by comparing P(S-SS 0.070 ) and P(S-MAA 0.072 ) ionomers. The ionic aggregates in P(S-SS 0.070 )-Cu are surrounded by a thicker region of limited mobility and are more ionic as compared with P(S-MAA 0.072 ) ionomers. Although STEM and X-ray scattering have been reconciled for these P(S-SS x ) ionomers, a broad application of the liquidlike hard-sphere scattering model is not recommended. However, when STEM and X-ray scattering are reconciled, detailed morphological information can be extracted from the scattering data, particularly regarding the composition of the ionic aggregates, which is important for understanding the mechanisms of ion transport.