Multiple computational and experimental techniques are used to understand the nanoscale morphology and water/proton transport properties in a series of sulfonated Diels–Alder poly­(phenylene) (SDAPP) membranes over a wide range of temperature, hydration, and sulfonation conditions. New synthetic methods allow us to sulfonate the SDAPP membranes to much higher ion exchange capacity levels than has been previously possible. Nanoscale phase separation between the hydrophobic polymer backbone and the hydrophilic water/sulfonic acid groups was observed for all membranes studied. We find good agreement between structure factors calculated from atomistic molecular dynamics (MD) simulations and those measured by X-ray scattering. With increasing hydration, the scattering ionomer peak in SDAPP is found to decrease in intensity. This intensity decrease is shown to be due to a reduction of scattering contrast between the water and polymer and is not indicative of any loss of nanoscale phase separation. Both MD simulations and density functional theory (DFT) calculations show that as hydration levels are increased, the nanostructure morphology in SDAPP evolves from isolated ionic domains to fully percolated water networks containing progressively weaker hydrogen bond strengths. The conductivity of the membranes is measured by electrical impedance spectroscopy and the equivalent proton conductivity calculated from pulsed-field-gradient (PFG) NMR diffusometry measurements of the hydration waters. Comparison of the measured and calculated conductivity reveals that in SDAPP the proton conduction mechanism evolves from being dominated by vehicular transport at low hydration and sulfonation levels to including a significant contribution from the Grötthuss mechanism (also known as structural diffusion) at higher hydration and sulfonation levels. The observed increase in conductivity reflects the impact that changing hydration and sulfonation have on the morphology and hydrogen bond network and ultimately on the membrane performance.

We report a new class of organoaluminum-based initiator for anionic ring-opening polymerization of epoxides that is simple to synthesize from readily available precursors. The resultant organometallic initiator was the triethyl­aluminum adduct of (2-dibenzyl­amino)­ethoxy­diethylaluminum (TAxEDA) [(AlEt3)·(O­(AlEt2)­CH2­CH2N­(Bn)2)], which was isolated by direct crystallization from the reaction medium and then compositionally and structurally characterized by NMR spectroscopy and XRD. We studied the reactivity and versatility of the new initiator through the polymerization of propylene oxide, butylene oxide, epichlorohydrin, and allyl glycidyl ether into homopolymer, statistical copolymer, and block copolymer architectures with heterobifunctional end-groups consisting of dibenzylamine and hydroxyl functionalities. The TAxEDA-initiated polymerizations were consistent with a controlled, living, anionic mechanism that was tolerant of chemical functionality and exhibited no chain transfer to monomer that limits the traditional anionic ring-opening polymerization of substituted epoxides.

We present an improvement in the rate, utility, and mechanistic understanding of mono-μ-oxo-dialuminum initiators for epoxide ring-opening polymerization.

A combined theoretical and experimental investigation into the structure and mechanism of the classical Vandenberg catalyst for the isoselective polymerization of epoxides has led to a consistent mechanistic proposal. The most likely reaction pathway was based on a bis(μ-oxo)di(aluminum) (BOD) resting state that proceeded through a mono(μoxo)di(aluminum) (MOD) transition state. The isoselectivity of the Vandenberg catalyst was derived from the rigidity of the BOD structure and its bonding to the ultimate and penultimate oxygen heteroatoms along the polyether backbone. The energetic driving force for isoselectivity was the loss of an energetically favorable secondary Al−O interaction during enchainment of oppositely configured epoxides, providing a ca. 2 kcal/mol driving force for the emergent isoselectivity. Experimental spectroscopic and kinetic evidence based on model BOD and MOD complexes support the new mechanistic framework developed using density functional theory calculations. A purposefully synthesized BOD analogue of the proposed Vandenberg structure produced a characteristically isotactically enriched poly(allyl glycidyl ether) as produced by the classical Vandenberg catalyst. In situ 1 H NMR spectroscopy of a Vandenberg-catalyzed polymerization of allyl glycidyl ether revealed the activation enthalpy (ΔH ‡ = 21 kcal/mol) and energetics of epoxide−aluminum coordination (ΔH = −4.0 ± 1.0 kcal/mol, ΔS = −0.018 ± 0.004 kcal/(K mol)) by observation of the shifting acetylacetonate signal located on the active site of the Vandenberg catalyst in the 1 H NMR spectra of polymerization.

We report an effective strategy for the synthesis of semi-crystalline block copolyethers with well-defined architecture and stereochemistry. As an exemplary system, triblock copolymers containing either atactic (racemic) or isotactic (R or S) poly(propylene oxide) end blocks with a central poly(ethylene oxide) mid-block were prepared by anionic ring-opening procedures. Stereochemical control was achieved by an initial hydrolytic kinetic resolution of racemic terminal epoxides followed by anionic ring-opening polymerization of the enantiopure monomer feedstock. The resultant triblock copolymers were highly isotactic (meso triads [mm]% ~ 90%) with optical microscopy, differential scanning calorimetry, wide angle x-ray scattering and small angle x-ray scattering being used to probe the impact of the isotacticity on the resultant polymer and hydrogel properties.

The addition of a diglycidyl-ether to a mono(μ-alkoxo)bis-(alkylaluminum)-initiated epoxide polymerization presents a strategy for amorphous polyether-based membrane synthesis. In situ kinetic 1 H NMR spectroscopy was used to monitor model network copolymerizations of epichlorohydrin (ECH) with 1,4butanediol-diglycidyl ether (Butyl-dGE) or poly(ethylene oxide)-diglycidyl ether (PEO-dGE). Reactivity ratios were extracted from the evolution of polymer composition from the monomer feed during copolymerization. Quantitative conversion and nearly random comonomer incorporation was achieved. The generality of this synthetic technique was supported by the polymerization of Butyl-dGE and a range of epoxide monomers such as n-butyl glycidyl ether (nBGE), allyl glycidyl ether, ECH, and glycidol. The copolymerizations produced optically clear, flexible films in all cases. We investigated the potential for this synthetic platform to provide compositional control of structure−property relationships within the context of industrially relevant membrane separations for CO 2 . Given the affinity of PEO for CO 2 and water, we explored using nBGE as a hydrophobic diluent, which was copolymerized with varying incorporations of PEO-dGE. The resultant cross-linked polyether membranes exhibited high CO 2 permeabilities (150−300 barrer) and selectivity over N 2 (α CO 2 /N 2 = 20−30) and H 2 (α CO 2 /H 2 ≈ 6). CO 2 sorption isotherms could be described by Henry's law and did not vary across the series of nBGE/PEO-dGE films. The similar sorption coefficients suggested that differences in permeability among these samples were driven by differences in diffusion coefficients. The diffusivity of CO 2 increased with cross-link density, and permeability was unaffected by humidity for this series of hydrophobic cross-linked polyether membranes.

An amphiphilic block copolymer surfactant is used to impart modifiable surface functionality to polymer nanoparticles synthesized via emulsion polymerization.

Crystal engineered organic frameworks assembled using hydrogen bonding are known, and examples constructed from hydroxypyridine/pyridone as the dominant source of hydrogen bonding have been reported. Less explored are analogous systems based on maleic hydrazide. Herein, a two-step route (Mitsunobu followed by Schiff base reactions) to asymmetrically substituted pyridazinones from maleic hydrazide (step 1) is reported with 2-, 3-, or 4-pyridinecarboxaldehyde (step 2). Upon reaction with 4-pyridinecarboxaldehyde, single crystals suitable for analysis via X-ray diffraction were obtained. Careful examination of this solid state structure and comparison with a large number of related structures in the Cambridge Structural Database revealed a pyridazinone (vs. pyridazinol) core and persistent [Formula: see text] “head-to-tail” hydrogen bonded dimers. Although these pyridazinones were originally considered suitable for use as ligands for metal cation coordination, challenges in achieving this outcome were encountered.