Temperature‐ and Voltage‐Induced Ligand Rearrangement of a Dynamic Electroluminescent Metallopolymer

A dynamic‐covalent metal‐containing polymer was synthesized by the condensation of linear diamine and dialdehyde subcomponents around copper(I) templates in the presence of bidentate phosphine ligands. In solution, the red polymers undergo a sol–gel transition upon heating to form a yellow gel, a process that can be either reversible or irreversible depending on the solvent used. When fabricated into a light‐emitting electrochemical cell (LEC), the polymer emits infrared light at low voltage. As the voltage is increased, a blue shift in the emission wavelength is observed until yellow light is emitted, a process which is gradually reversed over time upon lowering the voltage. The mechanism underlying these apparently disparate responses is deduced to be due to loss of the copper phosphine complex from the polymer.     

Synthesis of poly(propylene glycol)-block-polyethylenimine triblock copolymers for the delivery of nucleic acids

LPEIs, which are efficient DNA transfection agents, were found to be far less effective for the delivery of siRNAs. Here, two amphiphilic triblock copolymers LPEI(50) -b-PPG(36) -b-LPEI(50) (2) and LPEI(14) -b-PPG(68) -b-LPEI(14) (4) have been synthesized. The transfection assays showed that compound 2 was efficient for DNA transfection whilst it was almost inactive for siRNA delivery. In contrast, polymer 4 was inefficient for DNA transfection while it showed capabilities for siRNA delivery. Taken together, our results indicate that the properties required for DNA and siRNA delivery are different. Moreover, we show that introduction of a hydrophobic segment that allows self-assembly confers siRNA delivery capacities.     

High molecular weight polyacrylamides by atom transfer radical polymerization: Enabling advancements in water‐based applications

Through the use of copper (I) chloride (CuCl) and tris(2‐dimethylaminoethyl)amine (Me₆‐TREN) as a metal/ligand pair, conditions for the robust, fast, and controlled radical polymerization of high molecular weight N‐hydroxyethylacrylamide (HEAm),N‐isopropylacrylamide (NIPAm), N,N′‐dimethylacrylamide (DMAm), and acrylamide (Am) at ambient temperature are reported. Linear evolution of molecular weight and narrow molecular weight distribution was observed for all monomers with degrees of polymerization ranging from 50 to 5000. Random copolymers of several acrylamide‐based monomers are also reported with excellent control over molecular weight and polydispersity. Characterization of high molecular weight poly (NIPAm) demonstrated large changes in the lower critical solution temperature observed on heating and cooling, and this hysteresis was exploited for the controlled release of doxorubicin from poly(NIPAm) spheres. This study represents the first example of preparation of high molecular weight acrylamide polymers by a metal‐mediated controlled radical polymerization technique. Access to these materials, as well as to NIPAm polymers in particular, opens new doors for interesting applications in a variety of fields including tissue engineering, drug delivery, and controlled solution viscosity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Correction to: Identifying Efficient Transport Pathways in Early‑Wood Timber: Insights from 3D X‑ray CT Imaging of Softwood in the Presence of Flow

Transport in Porous Media - A correction to this paper has been published: https://doi.org/10.1007/s11242-021-01569-3     

Single-site binding of pyrene to poly(ester-imide)s incorporating long spacer-units: prediction of NMR resonance-patterns from a fractal model

Co-polycondensation of the diimide-based diols N,N′-bis(2-hydroxyethyl)hexafluoroisopropylidene-diphthalimide, (HFDI), and N,N′-bis(2-hydroxy-ethyl)naphthalene-1,4,5,8-tetracarboxylic-diimide, (NDI), with aliphatic diacyl chlorides ClOC(CH₂)_xCOCl (x = 5 to 8) affords linear copoly(ester-imide)s. Such copolymers interact with pyrene via supramolecular binding of the polycyclic aromatic at NDI residues. This interaction results in upfield complexation shifts and sequence-related splittings of the NDI ¹H NMR resonances, but gives a very different final resonance-pattern from the copolymer where x = 2. Computational modelling of the polymer with x = 5 suggests that each pyrene molecule binds to just a single NDI residue rather than by intercalation between a pair of NDI''s at a tight chain-fold, as was found for x = 2. The new single-site binding model enables the pattern of ¹H NMR resonances for copolymers with longer spacers (x = 5 to 8) to be reproduced and assigned by simulation from sequence-specific shielding factors based on a type of fractal known as the last-fraction Cantor set. As this type of fractal also enables an understanding of pairwise binding systems, it evidently provides a general numerical framework for supramolecular sequence-analysis in binary copolymers.

Nine ¹H NMR resonances assignable to specific copoly(ester-imide) sequences identified from a fractal model result from 1 : 1 supramolecular binding of pyrene to NDI residues.     

Supramolecular polymeric hydrogels

The supramolecular crosslinking of polymer chains in water by specific, directional and dynamic non-covalent interactions has led to the development of novel supramolecular polymeric hydrogels. These aqueous polymeric networks constitute an interesting class of soft materials exhibiting attractive properties such as stimuli-responsiveness and self-healing arising from their dynamic behaviour and that are crucial for a wide variety of emerging applications. We present here a critical review summarising the formation of dynamic polymeric networks through specific non-covalent interactions, with a particular emphasis on those systems based on host-guest complex formation, as well as the characterisation of their physical characteristics. Aqueous supramolecular chemistry has unlocked a versatile toolbox for the design and fine-tuning of the material properties of these hydrogels (264 references).