Zwitterionic Ring Opening Polymerization with Isothioureas

Bicyclic isothioureas <b>1</b> and <b>2</b> mediate controlled ring opening polymerizations (ROP) of lactides in the absence of protic initiators to afford high molecular weight polylactides (PLA) with narrow polydispersities. The cyclic structure of the resulting PLA was determined by dilute solution viscosity measurement and MALDI-TOF mass spectrometry. Compared to DBU initiator, isothioureas are more selective for producing cyclic PLA without appreciable linear contaminants. Mechanistic studies involving acyl amidinium support our hypothesis that DBU-initiated ZROP generates linear chains from a ketene aminal intermediate

1,2-Dithiolane-Derived Dynamic, Covalent Materials: Cooperative Self-Assembly and Reversible Cross-Linking

The use of dithiolane-containing polymers to construct responsive and dynamic networks is an attractive strategy in material design. Here, we provide a detailed mechanistic study on the self-assembly and gelation behavior of a class of ABA triblock copolymers containing a central poly­(ethylene oxide) block and terminal polycarbonate blocks with pendant 1,2-dithiolane functionalities. In aqueous solution, these amphiphilic block copolymers self-assemble into bridged flower micelles at high concentrations. The addition of a thiol initiates the reversible ring-opening polymerizations of dithiolanes in the micellar cores to induce the cross-linking and gelation of the micellar network. The properties of the resulting hydrogels depend sensitively on the structures of 1,2-dithiolanes. While the methyl asparagusic acid-derived hydrogels are highly dynamic, adaptable, and self-healing, those derived from lipoic acid are rigid, resilient, and brittle. The thermodynamics and kinetics of ring-opening polymerization of the two dithiolanes were investigated to provide important insights on the dramatically different properties of the hydrogels derived from the two different dithiolanes. The incorporation of both dithiolane monomers into the block copolymers provides a facile way to tailor the properties of these hydrogels

Structurally Dynamic Hydrogels Derived from 1,2-Dithiolanes

The design and generation of adaptable materials derived from structurally dynamic polymers provides a strategy for generating smart materials that can respond to environmental stimuli or exhibit self-healing behavior. Herein we report an expedient organocatalytic ring-opening polymerization of cyclic carbonates containing pendant dithiolanes (trimethylene carbonate/dithiolane, TMCDT) from poly­(ethylene oxide) diols to generate water-soluble triblock (ABA) copolymers containing a central poly­(ethylene oxide) block and terminal dithiolane blocks. Hydrogels generated from the triblock copolymers and a cross-linking dithiol exhibited dynamic behavior as a result of the reversible ring opening of the pendant 1,2-dithiolanes. These materials exhibit self-healing behavior, can be injected through a syringe, and rapidly recover their mechanical properties after a severe strain deformation. The dynamic properties of these gels can be modulated with the number of dithiolane units, pH, and temperature

Different Timing Features in Brain Processing of Core and Moral Disgust Pictures: An Event-Related Potentials Study

<div><p>Disgust, an emotion motivating withdrawal from offensive stimuli, protects us from the risk of biological pathogens and sociomoral violations. Homogeneity of its two types, namely, core and moral disgust has been under intensive debate. To examine the dynamic relationship between them, we recorded event-related potentials (ERPs) for core disgust, moral disgust and neutral pictures while participants performed a modified oddball task. ERP analysis revealed that N1 and P2 amplitudes were largest for the core disgust pictures, indicating automatic processing of the core disgust-evoking pictures. N2 amplitudes were higher for pictures evoking moral disgust relative to core disgust and neutral pictures, reflecting a violation of social norms. The core disgust pictures elicited larger P3 and late positive potential (LPP) amplitudes in comparison with the moral disgust pictures which, in turn, elicited larger P3 and LPP amplitudes when compared to the neutral pictures. Taken together, these findings indicated that core and moral disgust pictures elicited different neural activities at various stages of information processing, which provided supporting evidence for the heterogeneity of disgust.</p></div

Results of ANOVA for the amplitudes of N1, P2, N2, P3 and LPP components.

<p>Results of ANOVA for the amplitudes of N1, P2, N2, P3 and LPP components.</p

The reaction times and accuracies for three types of stimuli (<i>M±SD</i>).

<p>The reaction times and accuracies for three types of stimuli (<i>M±SD</i>).</p

The schematic illustration of the experimental procedure.

<p>Core disgust: vomit. Moral disgust: a bad antisocial action, a person stamping on a disabled beggar. Picture presentation was terminated by a key pressing or when 1000 ms was elapsed.</p

Topographical maps of voltage amplitudes of N1, P2, N2, P3 and LPP across three conditions.

<p>Topographical maps of voltage amplitudes of N1, P2, N2, P3 and LPP across three conditions.</p

Stimulus-locked grand average ERP waveforms.

<p>Grand average ERP waveforms recorded from Fz, FCz, Cz, CPz and Pz in response to core disgust (black lines), moral disgust (red lines) and neutral (blue lines) pictures.</p

Three-Dimensional Self-Assembly of Core/Shell-Like Nanostructures for High-Performance Nanocomposite Permanent Magnets

Core/shell nanostructures are fascinating for many advanced applications including strong permanent magnets, magnetic recording, and biotechnology. They are generally achieved via chemical approaches, but these techniques limit them to nanoparticles. Here, we describe a three-dimensional (3D) self-assembly of core/shell-like nanocomposite magnets, with hard-magnetic Nd₂Fe₁₄B core of ∼45 nm and soft-magnetic α-Fe shell of ∼13 nm, through a physical route. The resulting Nd₂Fe₁₄B/α-Fe core/shell-like nanostructure allows both large remanent magnetization and high coercivity, leading to a record-high energy product of 25 MGOe which reaches the theoretical limit for isotropic Nd₂Fe₁₄B/α-Fe nanocomposite magnets. Our approach is based on a sequential growth of the core and shell nanocrystals in an alloy melt. These results make an important step toward fabricating core/shell-like nanostructure in 3D materials