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.

A modular one-component supramolecular transient network in water, based on poly(ethylene glycol) and end-capped with four-fold hydrogen bonding units, is reported. Due to its nonlinear structural formation, this system allows active proteins to be added to the hydrogel during formation. Once implanted in vivo it releases the protein by erosion of both the protein and polymer via dissolution.

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.

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The aim of this study is to revisit the characterization of entanglement density in polyethylene melts by studying a series of well-defined, high molecular weight polyethylene materials via transverse NMR relaxometry in the melt state at 423 K. The comparison of the relaxometry data with high temperature SEC-MALLS characterization allows the measurement and correlation of the fraction of chain-end fragments by two independent methods. As compared with rheological methods that measure volume average characteristics, the 1H NMR method described here offers advantages for studying the entanglement molecular weight (M e) and chain dynamics in entangled polyethylene melts due to the selectivity of dynamics to entangled chain fragments and disentangled chain-end blocks. The calculated M e value for infinitely long chains equals 1760 ± 80 g/mol. This value is in the range of previously reported M e for polyethylene; however, it exceeds commonly accepted in rheology M e of 1250 g/mol. The difference can be explained (1) by the effect of chain branching and molecular weight distribution, if samples are not well characterized, and (2) by complex chain dynamics in polymer melts that require several assumptions in rubber-elasticity theory used for calculation of M e from the plateau modulus.

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Lamella thickness distribution (LTD) plays a critical role in determining the mechanical properties of polyethylene. LTD is predominantly governed by the intermolecular chemical composition distribution, but intrachain heterogeneity also results in a broadened LTD. Polyethylene synthesized by acyclic diene metathesis (ADMET) contains pristine microstructures free from inter and intrachain heterogeneity and therefore represent ideal models to investigate these phenomena. The crystalline structures of ADMET polyethylene with ethyl or n-hexyl branches every 21 st backbone carbon (EB21and EO21, respectively) were characterized by transmission electron microscopy (TEM), small X-ray scattering and wide angle X-ray diffraction (SAXS and WAXD), and differential scanning calorimetry (DSC). The samples were crystallized for various periods at temperatures near the DSC crystallization peak temperatures: 10 8C for EB21 and 0 8C for EO21. TEM observation exhibited that EB21 displays straight lamellar crystals with axialitic organization and an average thickness of about 55 Å. This corresponds to twice the ethylene sequence length between branches, suggesting that one lamellar stem spans three branches and includes one ethyl branch within the lamella. The lamella thickness distribution was very narrow compared with that of the cross-fraction of ethylene/1-butene copolymer prepared via Ziegler-Natta polymerization. Similarly it was found from the same characterization methods that EO21 also displays a narrow lamella thickness distribution albeit with thinner lamellae, averaging 25-26Å thick. Judging from this lamella thickness, EO21 is considered to have a lamella stem composed of a single ethylene sequence between two braches, suggesting that the n-hexyl branch is entirely excluded from a crystalline phase.

Two sequenced ethylene-propylene (EP) copolymers possessing methyl groups every fifth (EP5) or seventh (EP7) carbon have been prepared using an olefin metathesis polycondensation/hydrogenation strategy, thus generating methyl branched polyolefins with short ethylene run lengths of 4 or 6 carbons, respectively. Precise spacing of methyl branches along both copolymer backbones imparts pristine microstructure and targeted comonomer ratios in the copolymer. Extensive NMR spectral data are presented detailing polymer microstructure, branching analysis, and end-group identification. Thermal analysis using differential scanning calorimetry revealed multiple low-temperature relaxations for EP7 and glass transition temperature of -63 °C for EP5, and FT-IR analysis suggests no crystallinity under ambient conditions. A new ADMET monomer synthesis is also reported for the development of highly functionalized polyolefins or sequenced ethylene copolymers.