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

A mono(μ-oxo)bis(alkylaluminum) (MOB) catalyst and initiator for epoxide polymerization, [(H 3 C) 2 NCH 2 CH 2 (μ 2 -O)Al(iBu) 2 •Al(iBu) 3 ] (1), produced a ca. 170-fold enhancement in epoxide polymerization rate over previously reported MOB initiators demonstrated with allyl glycidyl ether (AGE). This discovery reduces polymerization times to minutes. 1 exhibited an exponential dependence of polymerization rate on concentration, rather than an expected low integer order relationship. A proposed polymerization intermediate was identified via direct synthesis, isolation, kinetic comparison, and corroborating in situ spectroscopic evidence to be a symmetric bis((μ-alkoxo)dialkylaluminum) (BOD) with a characteristic R 3 N•AlR′ 3 (N−Al) adduct. The N−Al adduct on the BOD intermediate is proposed to act as a catalyst, whereas the aluminoxane ring is proposed to be the site of monomer enchainment on the basis of mass spectrometry and spectroscopic analysis of resultant polymer structure. The distinct catalytic and initiation/propagation functionalities were separated into separate species, and the catalytic activity of the N−Al adduct was demonstrated in the presence of a distinct aluminoxane initiator. Each 1 equiv of N−Al adduct relative to initiator resulted in an abrupt (ca. 5−10fold) increase in the polymerization rate of AGE. The resultant N−Al adduct catalyst represents a versatile tool for rapid functional macromolecular synthesis.

We report a partial elucidation of the relationship between polymer polarity and ionic conductivity in polymer electrolyte mixtures comprising a homologous series of nine poly(vinyl ether)s (PVEs) and lithium bis(trifluoromethylsulfonyl)imide. Recent simulation studies have suggested that low dielectric polymer hosts with glass transition temperatures far below ambient conditions are expected to have ionic conductivity limited by salt solubility and dissociation. In contrast, high dielectric hosts are expected to have the potential for high ion solubility but slow segmental dynamics due to strong polymer−polymer and polymer−ion interactions. We report results for PVEs in the low polarity regime with dielectric constants of about 1.3 to 9.0. Ionic conductivity measured for the PVE and salt mixtures ranged from about 10 −10 to 10 −3 S/cm. In agreement with the predictions from computer simulations, the ionic conductivity increased with dielectric constant and plateaued as the dielectric approached 9.0, comparable to the dielectric constant of the widely used poly(ethylene oxide).

Establishing general structure−property relationships for polymer electrolytes is crucial to enable design of improved materials to advance solid-state energy storage. We report the relationship between dielectric constant, glass transition temperature, and ionic conductivity for polyether-based electrolytes with dielectric constants of the polyether host within the range 7−35 at 60 °C. The ionic conductivities of the polyether and lithium bis(trifluoromethylsulfonyl)imide mixtures ranged from 10 −7 to 10 −3 S/cm. In this higher-dielectric-constant regime, here defined as a polymer with a dielectric constant greater than that of poly(ethylene oxide) (ca. 9.0), the glass transition temperature increased with dielectric constant while ionic conductivity decreased. These results complement a recent report on the low-dielectric-constant regime, where the ionic conductivity was limited by the dielectric constant and ion dissociation. In the high-dielectric-constant regime explored here, segmental dynamics are slowed due to stronger polymer−polymer and polymer−ion interactions, resulting in decreased ionic conductivity and associated increase in neat polymer glass transition temperature. The disparate chemical structures of the polymers of this study, along with the results of past coarse-grained molecular dynamics simulations, support the generality of these conclusions and speak to the difficulty of identifying a single molecular characteristic leading to the design of high-conductivity polymer electrolytes. Widely used poly(ethylene oxide) represents a near-optimal balance between the low-and high-dielectric-constant regimes. To improve upon the ionic conductivity limitations of polymer electrolytes, single-component polymer hosts are unlikely to resolve the trade-off between the need for ion dissociation while retaining rapid segmental dynamics.

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Melanin-like compounds have been studied in recent years for their electron transport and ultraviolet (UV) light absorbance properties as well as applications as functional, biocompatible catalysts, and material additives. Pyomelanin is a unique form of melanin compounds that has not received significant attention. Here, a strain of Yarrowia lipolytica suitable for the production of nearly 2.8 g L −1 of homogentisic acid (HGA) is metabolically engineered, which can then be oxidized to form pyomelanin either in situ or through altering pH. By using this biosourced material, a series of material traits including spectral analysis/UV-vis absorbance properties, electronic and metal interaction/chelation properties, and effectiveness in polymer dispersions with poly(l-lactide) are evaluated. In all cases, biosourced pyomelanin performs on par with or better than a chemically sourced analog. In a performance application, it is explored how pyomelanin may be blended at low concentrations to increase the elasticity of a rigid commercial polymer. Collectively, this work establishes biosourced pyomelanin as a versatile compound for unique material applications.