This work demonstrates a new reactive and functional hybrid (S‐MMA‐POSS) of polyhedral oligomeric silsesquioxane (POSS) and sulfur prepared with a direct reaction between a multifunctional methacrylated POSS compound (MMA‐POSS) and elemental sulfur (S8) through the “inverse vulcanization” process. S‐MMA‐POSS is an effective building block for imparting self‐healing ability to the corresponding thermally crosslinked POSS‐containing nanocomposites through a self‐curing reaction and co‐curing reaction with conventional thermosetting resins. Moreover, S‐MMA‐POSS is also a useful precursor for preparation of materials with high transparency in mid‐infrared region.
This study reports the structural transition of electrospun poly(ε‐caprolactone) (PCL)/poly[(propylmethacryl‐heptaisobutyl‐polyhedral oligomeric silsesquioxane)‐co‐(methyl methacrylate)] (POSS‐MMA) blends, from PCL‐rich fibers, to bicontinuous PCL core/POSS‐MMA shell fibers, to POSS‐MMA‐rich fibers with a discontinuous PCL inner phase. A ternary phase diagram depicting the electrospinnability of PCL/POSS‐MMA solutions is constructed by evaluating the morphological features of fibers electrospun from solutions with various concentrations and PCL/POSS‐MMA blend ratios. X‐ray diffraction, Raman spectroscopy, and differential scanning calorimetry are further used to characterize the electrospun PCL/POSS‐MMA hybrid fibers. These physicochemical characterization results are thoroughly discussed to understand the internal structures of the hybrid fibers, which are directly correlated to the phase separation behavior of the electrospun solutions. The current study provides further insight into the complex phase behavior of POSS‐copolymer‐based systems, which hold great potential for a broad spectrum of biomedical applications.
Herein, it is demonstrated that star pseudopolyrotaxanes (star‐pPRs) obtained from the inclusion complexation of α‐cyclodextrin (CD) and four‐branched star poly(ε‐caprolactone) (star‐PCL) organize into nanoplatelets in dimethyl sulfoxide at 35 °C. This peculiar property, not observed for linear pseudopolyrotaxanes, allows the processing of star‐pPRs while preserving their supramolecular assembly. Thus, original PCL:star‐pPR core:shell nanofibers are elaborated by coaxial electrospinning. The star‐pPR shell ensures the presence of available CD hydroxyl functions on the fiber surface allowing its postfunctionalization. As proof of concept, fluorescein isothiocyanate is grafted. Moreover, the morphology of the fibers is maintained due to the star‐pPR shell that acts as a shield, preventing the fiber dissolution during chemical modification. The proposed strategy is simple and avoids the synthesis of polyrotaxanes, i.e., pPR end‐capping to prevent the CD dethreading. As PCL is widely used for biomedical applications, this strategy paves the way for simple functionalization with any bioactive molecules.
Multi‐micelle aggregation (MMA) mechanism is widely acknowledged to explicate large spherical micelles self‐assembly, but the process of MMA during self‐assembly is hard to observe. Herein, a novel kind of strong, regular microspheres fabricated from self‐assembly of amphiphilic anthracene‐functionalized β‐cyclodextrin (CD‐AN) via Cu(I)‐catalyzed azide‐alkyne click reactions is reported. The obtained CD‐AN amphiphiles can self‐assemble in water from primary core–shell micelles to secondary aggregates with the diameter changing from several tens nm to around 600–700 nm via MMA process according to the images of scanning electron microscopy, transmission electron microscopy, and atomic force microscopy as well as the dynamic light scattering measurements, followed by further crosslinking through photo‐dimerization of anthracene. What merits special attention is that such photo‐crosslinked self‐assemblies are able to disaggregate reversibly into primary nanoparticles when changing the solution conditions, which is benefited from the designed regular structure of CD‐AN and the rigid ranging of anthracene during assembly, thus confirming the process of MMA.
The preparation of multifunctional polymers and block copolymers by a straightforward one‐pot reaction process that combines enzymatic transacylation with light‐controlled polymerization is described. Functional methacrylate monomers are synthesized by enzymatic transacylation and used in situ for light‐controlled polymerization, leading to multifunctional methacrylate‐based polymers with well‐defined microstructure.
A new method for fabricating hydrogels with intricate control over hierarchical 3D porosity using microfiber porogens is presented. Melt electrospinning writing of poly(ε‐caprolactone) is used to create the sacrificial template leading to hierarchical structuring consisting of pores inside the denser poly(2‐oxazoline) hydrogel mesh. This versatile approach provides new opportunities to create well‐defined multilevel control over interconnected pores with diameters in the lower micrometer range inside hydrogels with potential applications as cell scaffolds with tunable diffusion and transport of, e.g., nutrients, growth factors or therapeutics.
Reversible addition–fragmentation chain transfer (RAFT) polymerization and characterization of an alkoxysilane acrylamide monomer using a trithiocarbonate chain transfer agent are described. Poly(N‐[3‐(trimethoxysilyl)propyl]acrylamide) (PTMSPAA) homopolymers are obtained with good control over the polymerization. A linear increase in the molecular weight is observed whereas the polydispersity values do not exceed 1.2 regardless of the monomer conversion. Moreover, PTMSPAA is used as a macro‐RAFT agent to polymerize N‐isopropylacrylamide (NIPAM). By varying the degree of polymerization of NIPAM within the block copolymer, different sizes of thermoresponsive particles are obtained. These particles are stabilized by the condensation of the alkoxysilane moieties of the polymers. Furthermore, a co‐network of silica and PTMSPAA is prepared using the sol–gel process. After drying, transparent mesoporous hybrids are obtained with a surface area of up to 400 m2 g−1.
High molecular weight cyclic poly(ε‐caprolactone)s (cPCLs) with variable ring size are synthesized via light‐induced ring closure of α,ω‐anthracene‐terminated PCL (An‐PCL‐An). The ring size of cPCL is tunable simply by adjusting the polymer concentration from 10 to 100 mg mL−1 in THF. The cycloaddition via the bimolecular cyclization of An‐PC‐An is well characterized by a variety of analyses such as 1H NMR and UV–vis spectroscopies, gel‐permeation chromatography, and differential scanning calorimetry. The reversible dimerization of An induced by heating enables the cyclic PCL to have a switchable “on–off” capability. This novel light‐induced ring‐closure technique can be one of the most powerful candidates for producing various well‐defined cyclic polymers in highly concentrated polymer solution.
A facile and versatile method for the synthesis of Janus graphene oxide (GO) nanosheets with different structures is reported. Based on electrostatic assembly, Janus GO nanosheets can be easily functionalized with a template polymer or be defunctionalized by altering the ionic strength. By using this approach, Janus GO nanosheets are prepared successfully with hydrophobic polystyrene chains on one side and hydrophilic poly(2‐(dimethylamino)ethyl methacrylate) chains on the other side.
Solvent vapor annealing (SVA) is originally developed to attain equilibrium nanostructures from microphase‐separated block polymer thin films. Interestingly, by carefully choosing a solvent vapor that can selectively mobilize the amorphous chains of a semicrystalline polymer while preserving the integrity of its crystalline structure, this study demonstrates that the SVA method can also be utilized to introduce hierarchical structures onto semicrystalline polymer‐based materials. This study on electrospun poly(ε‐caprolactone) (PCL) fibers clearly shows that acetone, a poor solvent for PCL, can effectively delocalize the amorphous chains and redeposit them onto the pre‐existing crystal edges, giving rise to secondary nanostructures inscribed onto the PCL fibers. In the past decade, various fiber fabrication methods and numerous fiber products are reported. The easy one‐step approach reported here provides new insight into the design and fabrication of structurally hierarchical polymeric materials.
A new and easy method of stimuli‐triggered growth and removal of a bioreducible nanoshell on nanoparticles is reported. The results show that pH or temperature could induce the aggregation of disulfide‐contained branched polymers at the surface of nanoparticles; subsequently, the aggregated polymers could undergo intermolecular disulfide exchange to cross‐link the aggregated polymers, forming a bioreducible polymer shell around nanoparticles. When these nanoparticles with a polymer shell are treated with glutathione (GSH) or d,l ‐dithiothreitol (DTT), the polymer shell could be easily removed from the nanoparticles. The potential application of this method is demonstrated by easily growing and removing a bioreducible shell from liposomes, and improvement of in vivo gene transfection activity of liposomes with a bioreducible PEG shell.
The excellent properties of elastomers are exploited to trigger wrinkling instabilities in curved shells. Micro‐ and nano‐fibres are produced by electrospinning and UV irradiated: each fibre consists of a soft core and a stiff outer half‐shell. Upon solvent de‐swelling, the fibres curl because the shell and the core have different natural lengths. Wrinkling only starts after the fibre has attained a well‐defined helical shape. A simple analytical model is proposed to find the curling curvature and wrinkle wavelength, as well as the transition between the “curling” and “wrinkling” regimes. This new instability resembles that found in the tendrils of climbing plants as they dry and lignify.
The temperature and pH‐dependent diffusion of poly(glycerol monomethacrylate)‐block‐poly(2‐hydroxypropyl methacrylate) nanoparticles prepared via polymerization‐induced self‐assembly in water is characterized using fluorescence correlation spectroscopy (FCS). Lowering the solution temperature or raising the solution pH induces a worm‐to‐sphere transition and hence an increase in diffusion coefficient by a factor of between four and eight. FCS enables morphological transitions to be monitored at relatively high copolymer concentrations (10% w/w) compared to those required for dynamic light scattering (0.1% w/w). This is important because such transitions are reversible at the former concentration, whereas they are irreversible at the latter. Furthermore, the FCS data suggest that the thermal transition takes place over a very narrow temperature range (less than 2 °C). These results demonstrate the application of FCS to characterize order–order transitions, as opposed to order–disorder transitions.
The formation of a poly(2,6‐carbazole) derivative during an electrochemical polymerization process is shown. Comparison of 3,5‐bis(9‐octyl‐9H‐carbazol‐2‐yl)pyridine and 3,5‐bis(9‐octyl‐9H‐carbazol‐3‐yl)pyridine by electrochemical and UV–Vis‐NIR spectroelectrochemical measurements and DFT (density functional theory) calculation prove the formation of a poly(2,6‐carbazole) derivative. Both of the compounds form stable and electroactive conjugated polymers.
Here, a novel method is demonstrated for the preparation of three‐arm branched microporous organic nanotube networks (TAB‐MONNs) based on molecular templating of three‐arm branched core–shell bottlebrush copolymers and Friedel–Crafts alkylation reaction. The unique three‐arm branched bottlebrush copolymers are synthesized by a combination of atom transfer radical polymerization, reversible addition‐fragmentation chain transfer polymerization, and ring‐opening polymerization techniques. In this approach, the length and diameter of branched tube units can be well‐controlled by rational molecular design. Moreover, the as‐prepared TAB‐MONNs possess a high surface area and exhibit a superior adsorption capacity for Rhodamine 6G (R6G) and p‐cresol.
The synthesis of symmetric cyclo poly(ε‐caprolactone)–block–poly(l (d )‐lactide) (c(PCL–b–PL(D)LA)) by combining ring‐opening polymerization of ε‐caprolactone and lactides and subsequent click chemistry reaction of the linear precursors containing antagonist functionalities is presented. The two blocks can sequentially crystallize and self‐assemble into double crystalline spherulitic superstructures. The cyclic chain topology significantly affects both the nucleation and the crystallization of each constituent, as gathered from a comparison of the behavior of linear precursors and cyclic block copolymers. The stereochemistry of the PLA block does not have a significant effect on the nonisothermal crystallization of both linear and cyclo PCL‐b‐PDLA and PCL‐b‐PLLA copolymers.
An alkyne‐functionalized ruthenium(II) bis‐terpyridine complex is directly copolymerized with phenylacetylene by alkyne polymerization. The polymer is characterized by size‐exclusion chromatography (SEC), 1H NMR spectroscopy, cyclic voltammetry (CV) measurements, and thermal analysis. The photophysical properties of the polymer are studied by UV–vis absorption spectroscopy. In addition, spectro‐electrochemical measurements are carried out. Time‐resolved luminescence lifetime decay curves show an enhanced lifetime of the metal complex attached to the conjugated polymer backbone compared with the Ru(tpy)22+ model complex.
Electrospinning is a well‐known technique for the preparation of scaffolds for biomedical applications. In this work, a continuous electrospinning method for gel fiber preparation is presented without a spinning window. As proof of concept, the preparation of poly(aspartic acid)‐based hydrogel fibers and their properties are described by using poly(succinimide) as shell polymer and 2,2,4(2,4,4)‐trimethyl‐1,6‐hexanediamine as cross‐linker in the core of the nozzle. Cross‐linking takes place as the two solutions get in contact at the tip of the nozzle. The impact of solution concentrations and feeding rates on fiber morphology, proof of the presence of cross‐links as well as pH sensitivity after the transformation of the poly(succinimide)‐based material to poly(aspartic acid) is presented.
A convenient synthetic approach for the preparation of uniform metallopolymer‐containing hollow spheres based on 2‐(methacryloyloxy)ethyl ferrocenecarboxylate (FcMA) as monomer by sequential starved feed emulsion polymerization is described. Core/shell particles consisting of a noncrosslinked poly(methyl methacrylate) core and a slightly crosslinked ferrocene‐containing shell allows for the simple dissolution of core material and, thus, monodisperse metallopolymer hollow spheres are obtained. Since PFcMA is incorporated in the particle shell, herein investigated hollow spheres can be addressed by external triggers, i.e., solvent variation and redox chemistry in order to change the particle swelling capability. PFcMA‐containing core/shell particles and hollow spheres are characterized by transmission electron microscope (TEM), scanning electron microscopy, cryogenic TEM, thermogravimetric analysis, and dynamic light scattering in terms of size, size distribution, hollow sphere character, redox‐responsiveness, and composition. Moreover, the general suitability of prepared stimulus‐responsive nanocapsules for the use in catch‐release systems is demonstrated by loading the nanocapsules with malachite green as model payload followed by release studies.
Temperature‐triggered switchable nanofibrous membranes are successfully fabricated from a mixture of cellulose acetate (CA) and poly(N‐isopropylacrylamide) (PNIPAM) by employing a single‐step direct electrospinning process. These hybrid CA‐PNIPAM membranes demonstrate the ability to switch between two wetting states viz. superhydrophilic to highly hydrophobic states upon increasing the temperature. At room temperature (23 °C) CA‐PNIPAM nanofibrous membranes exhibit superhydrophilicity, while at elevated temperature (40 °C) the membranes demonstrate hydrophobicity with a static water contact angle greater than 130°. Furthermore, the results here demonstrate that the degree of hydrophobicity of the membranes can be controlled by adjusting the ratio of PNIPAM in the CA‐PNIPAM mixture.
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