Cross‐linked silicone elastomers constructed with dynamic‐covalent boronic esters are first synthesized by photoinitiated radical thiol−ene “click” chemistry. The resultant samples can be cut with a sharp knife into two pieces and then healed via the reversibility of the boronic ester cross‐linkages to restore the original silicone sample within 30 min. Regulation of luminescent properties is achieved by incorporating organic dye into the elastomers through a “one‐pot” thiol–ene reaction. The proposed synthesis procedure demonstrates a new strategy to produce boronic acid silicone materials capable of self‐healing without external forces.
A novel and non‐cytotoxic self‐healing supramolecular elastomer (SE) is synthesized with small‐molecular biological acids by hydrogen‐bonding interactions. The synthesized SEs behave as rubber at room temperature without additional plasticizers or crosslinkers, which is attributed to the phase‐separated structure. The SE material exhibits outstanding self‐healing capability at room temperature and essential non‐cytotoxicity, which makes it a potential candidate for biomedical applications.
Since the development of supramolecular chemical biology, self‐organised nano‐architectures have been widely explored in a variety of biomedical applications. Functionalized synthetic molecules with the ability of non‐covalent assembly in an aqueous environment are typically able to interact with biological systems and are therefore especially interesting for their use in theranostics. Nanostructures based on π‐conjugated oligomers are particularly promising as theranostic platforms as they bear outstanding photophysical properties as well as drug loading capabilities. This Feature Article provides an overview on the recent advances in the self‐assembly of intrinsically fluorescent nanoparticles from π‐conjugated small molecules such as fluorene or perylene based chromophores for biomedical applications.
The present review focuses on the recent progress made in thin film orientation of semi‐conducting polymers with particular emphasis on methods using epitaxy and shear forces. The main results reported in this review deal with regioregular poly(3‐alkylthiophene)s and poly(dialkylfluorenes). Correlations existing between processing conditions, macromolecular parameters and the resulting structures formed in thin films are underlined. It is shown that epitaxial orientation of semi‐conducting polymers can generate a large palette of semi‐crystalline and nanostructured morphologies by a subtle choice of the orienting substrates and growth conditions.
Reversible addition‐fragmentation chain transfer polymerization yields reactive block copolymers bearing the pentafluorophenyl ester (PFPA) group, and subsequent Click amidation using 2,2,6,6‐tetramethylpiperidine‐N‐oxyl‐ and imidazolium‐functionalized primary amines produces the corresponding functional block copolymers, leading to installation of statistical radical‐ and ionic sites into the PFPA segment. The monolayered thin film devices fabricated using the obtained block copolymers exhibit repeatable switching of electric conductivity (on/off ratio > 103) under a bias voltage, which reveals that the coexistence of radicals and ions in the same spherical domain of the copolymer layer is a prerequisite for repeatable switching memory.
Cationic imidazolium‐functionalized polyethylene is accessible by insertion copolymerization of ethylene and allyl imidazolium tetrafluoroborate (AIm‐BF4) with phosphinesulfonato palladium(II) catalyst precursors. Imidazolium‐substituted repeat units are incorporated into the main chain and the initiating saturated chain end of the linear polymers, rather than the terminating unsaturated chain end. The counterion of the allyl imidazolium monomer is decisive, with the chloride analogue (AIm‐Cl) no polymerization is observed. Stoichiometric studies reveal the formation of an inactive chloride complex from the catalyst precursor. An effect of moderate densities (0.5 mol%) of ionic groups on the copolymers' physical properties is exemplified by an enhanced wetting by water.
In this study, a new type of functional, self‐assembled nanostructure formed from porphyrins and polyamidoamine dendrimers based on hydrogen bonding in an aqueous solution is presented. As the aggregates formed are promising candidates for solar‐energy conversion, their photocatalytic activity is tested using the model reaction of methyl viologen reduction. The self‐assembled structures show significantly increased activity as compared to unassociated porphyrins. Details of interaction forces driving the supramolecular structure formation and regulating catalytic efficiency are fundamentally discussed.
An extrinsic self‐healing coating system containing tetraphenylethylene (TPE) in microcapsules was monitored by measuring aggregation‐induced emission (AIE). The core healing agent comprised of methacryloxypropyl‐terminated polydimethylsiloxane, styrene, benzoin isobutyl ether, and TPE was encapsulated in a urea‐formaldehyde shell. The photoluminescence of the healing agent in the microcapsules was measured that the blue emission intensity dramatically increased and the storage modulus also increased up to 105 Pa after the photocuring. These results suggested that this formulation might be useful as a self‐healing material and as an indicator of the self‐healing process due to the dramatic change in fluorescence during photocuring. To examine the ability of the healing agent to repair damage to a coating, a self‐healing coating containing embedded microcapsules was scribed with a razor. As the healing process proceeded, blue light fluorescence emission was observed at the scribed regions. This observation suggested that self‐healing could be monitored using the AIE fluorescence.
The polymerization of ocimene has been first achieved by half‐sandwich rare‐earth metal dialkyl complexes in combination with activator and AliBu3. The regio‐ and stereoselectivity in the ocimene polymerization can be controlled by tuning the cyclopentadienyl ligand and the central metal of the complex. The chiral cyclopentadienyl‐ligated Sc complex 1 prepares syndiotactic cis‐1,4‐polyocimene (cis‐1,4‐selectivity up to 100%, rrrr = 100%), while the corresponding Lu, Y, and Dy complexes 2 – 4 and the achiral pentamethylcyclopentadienyl Sc, Lu, and Y complexes 5 – 7 afford isotactic trans‐1,2‐polyocimenes (trans‐1,2‐selectivity up to 100%, mm = 100%).
Several pyrene‐based polyphenylene dendrimers (PYPPDs) with different peripheral chromophores (PCs) are synthesized and characterized. Deep blue emissions solely from the core are observed for all of them in photoluminescence spectra due to good steric shielding of the core and highly efficient surface‐to‐core Förster resonant energy transfers (FRETs). Device performances are found in good correlation with the energy gaps between the work function of the electrodes and the frontier molecular orbital (FMO) levels of the PCs. Pure blue emission, luminance as high as 3700 cd m−2 with Commission Internationale de l'Éclairage 1931 (CIExy) = (0.16, 0.21), and a peak current efficiency of 0.52 cd A−1 at CIExy = (0.17, 0.20) are achieved. These dendrimers are among the best dendritic systems so far for fluorescent blue light‐emitting materials.
A facile homogeneous polymerization system involving the iniferter agent 1‐cyano‐1‐methylethyl diethyldithiocarbamate (MANDC) and copper(II) acetate (Cu(OAc)2) is successfully developed in bulk using methyl methacylate (MMA) as a model monomer. The detailed polymerization kinetics with different molar ratios (e.g., [MMA]0/[MANDC]0/[Cu(OAc)2]0 = 500/1/x (x = 0.1, 0.2, 0.5, 1.0)) demonstrate that this system has the typical “living”/controlled features of “living” radical polymerization, even with ppm level catalyst Cu(OAc)2, first order polymerization kinetics, a linear increase in molecular weight with monomer conversion and narrow molecular weight distributions for the resultant PMMA. 1H NMR spectra and chain‐extension experiments further confirm the “living” characteristics of this process. A plausible mechanism is discussed.
A self‐healing hydrogel is prepared by crosslinking acrylamide with a host–guest macro‐crosslinker assembled from poly(β‐cyclodextrin) nanogel and azobenzeneacrylamide. The photoisomerizable azobenzene moiety can change its binding affinity with β‐cyclodextrin, therefore the crosslinking density and rheology property of the hydrogel can be tuned with light stimulus. The hydrogel can repair its wound autonomously through the dynamic host–guest interaction. In addition, the wounded hydrogel will lose its ability of self‐healing when exposed to ultraviolet light, and the self‐healing behavior can be recovered upon the irradiation of visible light. The utilizing of host–guest macro‐crosslinking approach manifests the as‐prepared hydrogel reversible and light‐switchable self‐healing property, which would broaden the potential applications of self‐healing polymers.
Copolymers of 2‐(N,N‐dimethylamino)ethyl acrylate (DMAEA) and 2‐(tert‐Boc‐amino)ethyl acrylate (t BocAEA) are synthesized by reversible addition–fragmentation chain transfer polymerization in a controlled manner with defined molar masses and narrow molar masses distributions (Ð ≤ 1.17). Molar compositions of the P(DMAEA‐co‐t BocAEA) copolymers are assessed by means of 1H NMR. A complete screening in molar composition is studied from 0% of DMAEA to 100% of DMAEA. Reactivity ratios of both comonomers are determined by the extended Kelen–Tüdos method (r DMAEA = 0.81 and rtBocAEA = 0.99).
Star copolymers are known to phase separate on the nanoscale, providing useful self‐assembled morphologies. In this study, the authors investigate synthesis and assembly behavior of miktoarm star (μ‐star) copolymers. The authors employ a new strategy for the synthesis of unprecedented μ‐star copolymers presenting poly(N‐octyl benzamide) (PBA) and poly(ε‐caprolactone) (PCL) arms: a combination of chain‐growth condensation polymerization, styrenics‐assisted atom transfer radical coupling, and ring‐opening polymerization. Gel permeation chromatography, mass‐analyzed laser desorption/ionization mass spectrometry, and 1H NMR spectroscopy reveal the successful synthesis of a well‐defined (PBA11)2‐(PCL15)4 μ‐star copolymer (M n,NMR ≈ 12 620; Đ = 1.22). Preliminary examination of the PBA2PCL4 μ‐star copolymer reveals assembled nanofibers having a uniform diameter of ≈20 nm.
Exploiting the tremendous potential of the recently discovered reversible bidirectional shape‐memory effect (rbSME) for biomedical applications requires switching temperatures in the physiological range. The recent strategy is based on the reduction of the melting temperature range (ΔTm) of the actuating oligo(ε‐caprolactone) (OCL) domains in copolymer networks from OCL and n‐butyl acrylate (BA), where the reversible effect can be adjusted to the human body temperature. In addition, it is investigated whether an rbSME in the temperature range close or even above Tm,offset (end of the melting transition) can be obtained. Two series of networks having mixtures of OCLs reveal broad ΔTms from 2 °C to 50 °C and from −10 °C to 37 °C, respectively. In cyclic, thermomechanical experiments the rbSME can be tailored to display pronounced actuation in a temperature interval between 20 °C and 37 °C. In this way, the application spectrum of the rbSME can be extended to biomedical applications.
This work describes the synthesis of π‐conjugated polymers possessing arylene and 1,3‐butadiene alternating units in the main chain by the reaction of α,β‐unsaturated ester/nitrile containing γ‐H with aromatic/heteroaromatic aldehyde compound. By using 4‐(4‐formylphenyl)‐2‐butylene acid ethyl ester as a model monomer, the different polymerization conditions, including catalyst, catalyst amount, and solvent, are optimized. The polymerization of 4‐(4‐formylphenyl)‐2‐butylene acid ethyl ester is carried out by refluxing in ethanol for 72 h with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a catalyst to give a 1,3‐butadiene‐containing π‐conjugated polymer, poly(phenylene‐1,3‐butadiene), in 84.3% yield with and / (PDI) estimated as 6172 and 1.65, respectively. Based on this new methodology, a series of π‐conjugated polymers containing 1,3‐butadiene units with different substituents are obtained in high yields. A possible mechanism is proposed for the polymerization through a six‐membered ring transition state and then a 1,5‐H shift intermediate.
Multivalent binding is a key for many critical biological processes and unique recognition and specificity in binding enables many of different glycans and proteins to work in a great harmony within the human body. In this study, the binding kinetics of synthetic glycopolypeptides to the dendritic cell lectin DC‐SIGN and their inhibition potential for DC‐SIGN interactions with the gp120 envelope glycoprotein of HIV‐1 (gp120) are investigated.
The chemical control of cell division has attracted much attention in the areas of single cell‐based biology and high‐throughput screening platforms. A mussel‐inspired cytocompatible encapsulation method for achieving a “cell‐division control” with cross‐linked layer‐by‐layer (LbL) shells is developed. Catechol‐grafted polyethyleneimine and hyaluronic acid are chosen as polyelectrolytes for the LbL process, and the cross‐linking of polyelectrolytes is performed at pH 8.5. Cell division is controlled by the number of the LbL nanolayers and cross‐linking reaction. We also suggest a new measuring unit, , for quantifying “cell‐division timing” based on microbial growth kinetics.
The polymerisation of N‐acryloylmorpholine in water is reported utilising Cu(0)‐mediated living radical polymerisation (SET‐LRP). The inherent instability of [CuI(Me6‐Tren)Br] in aqueous solution is exploited via rapid disproportionation to prepare Cu(0) particles and [CuII(Me6‐Tren)Br2] in situ prior to addition of monomer and initiator. Quantitative conversion is attained within 30 min for various degrees of polymerisation (DPn = 20–640) with SEC showing symmetrical narrow molecular weight distributions (Đ < 1.18) in all cases. Optimised conditions are subsequently applied for the preparation of a diblock copolymer poly(NIPAm)‐b‐(N‐acryloylmorpholine), illustrating the versatility of this approach.
A new self‐healing polymer has been obtained by incorporating a cyclometalated platinum(II) complex Pt(C∧N∧N)Cl (C∧N∧N = 6‐phenyl‐2,2′‐bipyridyl) into a polydimethylsiloxane (PDMS) backbone. The molecular interactions (a combination of Pt···Pt and π–π interactions) between cyclometalated platinum(II) complexes are strong enough to crosslink the linear PDMS polymer chains into an elastic film. The as prepared polymer can be stretched to over 20 times of its original length. When damaged, the polymer can be healed at room temperature without any healants or external stimuli. Moreover, the self‐healing is insensitive to surface aging. This work represents the first example where the attractive metallophilic interactions are utilized to design self‐healing materials. Moreover, our results suggest that the stretchability and self‐healing properties can be obtained simultaneously without any conflict by optimizing the strength of crosslinking interactions.
