Azide/Alkyne‐“Click”‐Reactions of Encapsulated Reagents: Toward Self‐Healing Materials

The successful encapsulation of reactive components for the azide/alkyne‐“click”‐reaction is reported featuring for the first time the use of a liquid polymer as reactive component. A liquid, azido‐telechelic three‐arm star poly(isobutylene) ( = 3900 g · mol⁻¹) as well as trivalent alkynes were encapsulated into micron‐sized capsules and embedded into a polymer‐matrix (high‐molecular weight poly(isobutylene), = 250 000 g · mol⁻¹). Using (Cu^IBr(PPh₃)₃) as catalyst for the azide/alkyne‐“click”‐reaction, crosslinking of the two components at 40 °C is observed within 380 min and as fast as 10 min at 80 °C. Significant recovery of the tensile storage modulus was observed in a material containing 10 wt.‐% and accordingly 5 wt.‐% capsules including the reactive components within 5 d at room temperature, thus proving a new concept for materials with self‐healing properties.

     

Nanostructured Heteroarm Star Block Terpolymers via an Extension of the “In–Out” Polymerization Route

In this communication an extended “in–out” polymerization method is presented, which leads to the synthesis of novel heteroarm star block terpolymers of the type A_n(B‐b‐C)_n. A four step/one‐pot synthetic procedure is pursued using anionic polymerization under an inert atmosphere. The resulted star‐shaped terpolymer consists of a divinyl benzene nodule bearing pure polystyrene and poly(hexyl methacrylate)‐block‐poly(methyl methacrylate) diblock copolymer arms. It is shown that this kind of star terpolymers can self‐assemble in the bulk forming lamellae mesophase by arm and block segregation. The mechanical properties of the terpolymer have been examined in detail. Finally, the proposed synthetic procedure can be easily employed in other controlled polymerization methods.

     

‘Click’ Functionalization of Cryogels Conveniently Verified and Quantified Using High‐Resolution MAS NMR Spectroscopy

Chemical modification reactions of alkyne containing polyHEMA‐based macroporous network structures (cryogels) by Cu(I) catalyzed azide‐alkyne ‘click’ cycloaddition reactions and their monitoring and quantification with high‐resolution magic angle spinning (hr‐MAS) NMR spectroscopy are reported. Complete conversion is obtained when benzylazide is reacted with the grafted alkyne function, but only partial conversion is observed when using azide‐modified poly(ethylene glycol) (PEG‐N₃). Subsequent addition of benzylazide consumes all remaining alkyne groups. All chemical modifications are easily monitored at each stage using hr‐MAS NMR spectroscopy. The alkyne functionality and the resulting triazole ring provide well resolved ¹H resonances to monitor and quantify the progress of such ‘click’ reactions in general.

     

Application of Poly(3‐hexylthiophene) Functionalized with an Anchoring Group in Dye‐sensitized Solar Cells

A series of three poly(3‐hexylthiophene) functionalized either with a cyanoacetic acid (CA) or a rhodanine‐3‐acetic acid anchoring groups were synthesized and characterized. The TiO₂ based dye‐sensitized solar cells have been fabricated and performances were tested. We show that shorter chain length (15 thiophene units) linked to CA binding group gives good performances as J_sc, V_oc, FF and η(%) were 6.93(mA · cm⁻²), 0.65(V), 0.67 and 3.02%, respectively. A maximum IPCE of ≈50% at 500 nm was recorded with a liquid electrolyte, under AM 1.5 simulated solar irradiance.

     

Novel Amphiphilic Degradable Poly(ε‐caprolactone)‐graft‐poly(4‐vinyl pyridine), Poly(ε‐caprolactone)‐graft‐poly(dimethylaminoethyl methacrylate) and Water‐Soluble Derivatives

New amphiphilic graft copolymers that have a poly(ε‐caprolactone) (PCL) biodegradable hydrophobic backbone and poly(4‐vinylpyridine) (P4VP) or poly(2‐(N,N‐dimethylamino)ethyl methacrylate) (PDMAEMA) hydrophilic side chains have been prepared by anionic polymerization of the corresponding 4VP and DMAEMA monomers using a PCL‐based macropolycarbanion as initiator. The water solubility of these amphiphilic copolymers is improved by quaternization, which leads to fully water‐soluble cationic copolymers that give micellar aggregates in deionized water with diameters ranging from 65 to 125 nm. In addition, to improve the hydrophilicity of PCL‐g‐P4VP, grafting of poly(ethylene glycol) (PEG) segments has been carried out to give a water‐soluble double grafted PCL‐g‐(P4VP;PEG) terpolymer.

     

Encapsulation of Bovine Serum Albumin in Temperature‐Programmed “Shell‐in‐Shell” Structures

A novel approach to load a hydrophilic bovine serum albumin into drug carriers was proposed in terms of temperature‐programmed “shell‐in‐shell” structures, which were fabricated with poly(N‐isopropylacrylamide), poly(lactide), poly(ethylene glycol), and Au nanoparticles. Spherically well‐defined “shell‐in‐shell” structures were constructed by a modified‐double‐emulsion method (MDEM). The lower critical solubility temperature of the structures was manipulated to 36.4 °C which was confirmed by UV/Vis spectroscopy and DSC (Differential Scanning Calorimetry).

TEM image of the Au@PLLA‐PEG@PNIPAAm‐PDLA structure.     

Synthesis of Well‐defined Amphiphilic Block Copolymers by Organotellurium‐Mediated Living Radical Polymerization (TERP)

Low‐molecular weight amphiphilic diblock copolymers, polystyrene‐block‐poly (2‐vinylpyridine) (PS‐b‐P2VP), and (P2VP‐b‐PS) with different block ratios were synthesized for the first time via organotellurium‐mediated living radical polymerization (TERP). For both the homo‐ and block copolymerizations, good agreement between the theoretical, and experimental molecular weights was found with nearly 100% yield in every case. The molecular weight distribution for all the samples ranged between 1.10 and 1.24, which is well below the theoretical lower limit of 1.50 for a conventional free radical polymerization. Furthermore, a very simple approach to producing highly dense arrays of titania nanoparticles (TiO₂) is presented using a site‐selective reaction of titanium tetraisopropoxide within the P2VP domains of micellar film of P2VP‐b‐PS in toluene through the sol–gel method.

     

Hairy PEO‐Silica Nanoparticles through Surface‐Initiated Polymerization of Ethylene Oxide

Summary: The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles was performed in situ by the ring‐opening polymerization of the oxirane monomer initiated from the mineral surface using aluminium isopropoxide as an initiator/heterogeneous catalyst. Alcohol groups were first introduced onto silica by reacting the surfacic silanols with prehydrolyzed 3‐glycidoxypropyl trimethoxysilane. The alcohol‐grafted silica played the role of a coinitiator/chain‐transfer agent in the polymerization reaction and enabled the formation of irreversibly bonded polymer chains. Silica nanoparticles containing up to 40 wt.‐% of a hairy layer of grafted PEO chains were successfully produced by this technique.

The grafting of poly(ethylene oxide) (PEO) onto silica nanoparticles by in‐situ ring‐opening polymerization of the oxirane monomer.     

1,1‐Diphenyl Ethylene‐Mediated Radical Polymerisation: A General Non‐Metal‐Based Technique For The Synthesis Of Precise Core Cross‐Linked Star Polymers

This communication details the successful synthesis of low polydispersity core cross‐linked star (CCS) polymers via DPE‐mediated polymerisation. We demonstrate the ability to produce poly(methyl methacrylate) and poly(acrylonitrile) CCS polymers that are currently inaccessible via the two most common non‐metal‐based controlled radical polymerisation techniques (NMP and RAFT polymerisations).

     

Facile Synthesis of Glycopolypeptides by Combination of Ring‐Opening Polymerization of an Alkyne‐Substituted N‐carboxyanhydride and Click “Glycosylation”

Synthetic glycopolypeptides have attracted much interest for application in biomedical field as they are structural mimics to the natural glycopeptides or glycoproteins. However, the synthesis methods toward glycopolypeptides are still few or less efficient. Herein, we present a facile route to preparation of glycopolypeptides with highly effective “glycosylation” by click postpolymerization modification. First, an alkyne‐substituted N‐carboxyanhydride (NCA) monomer was synthesized and subsequently polymerized to afford the polypeptide with “clickable” alkyne pendants. The alkyne‐functionalized polypeptide was then “glycosylated” by click reaction of different sugar azides to the alkyne pendants with high efficiency. All the obtained glycopolypeptides were soluble and preferred α‐helix conformation in water. Primary studies on the obtained glycopolypeptides binding with Con A lectin were assessed by turbidimetric assay. The more quantitive studies of the interactions between lectin proteins and the synthetic glycopolypeptides, and the application of these materials as the multivalent ligands are in progress.

     

Self‐Assembly Pluronic and β‐Cyclodextrin to Hollow Nanospheres for Enhanced Gene Delivery

This paper studies a kind of hollow nanospheres prepared by self‐assembly β‐cyclodextrins (β‐CDs) and poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (pluronic F127) for gene delivery. It was found that this kind of hollow nanospheres enable load PEI10K/DNA and the resulting F127 NH₂ βCD/(PEI10K/DNA) with 0.08 µg/well DNA display equal or higher gene delivery capability compared to PEI10K/DNA with 1 µg/well DNA in the absence or presence of serum. The cytotoxicity of the nanospheres was over 100 times lower than that of PEI10K.

     

A Mechanochemical Approach to Nanocomposites Using Single‐Wall Carbon Nanotubes and Poly(L‐lysine)

A simple method to fabricate polymer nanocomposites with single‐walled carbon nanotubes is reported, in which the nanotubes were reacted with poly(L ‐lysine) by using high‐speed vibration milling. The nanocomposites obtained were characterized by Fourier transform infrared (FT‐IR), UV–Vis spectroscopy, and thermogravimetric methods. The morphology as well as the dispersion of the carbon nanotubes were determined by scanning and transmission electron microscopy.

     

A Facile Route to Prepare Organic/Inorganic Hybrid Nanomaterials by ‘Click Chemistry’

An organosilane with an alkyne group at the non‐condensable end, [(2‐propynylcarbamate)propyl]triethoxysilane, has been synthesized. Condensation of this organosilane with tetraethoxysilane can be achieved by a co‐condensation strategy to produce silica nanoparticles with surface alkyne functionality. The size and uniformity of size distribution of the silica nanoparticles are influenced by varying the concentration of the added organosilane. The alkyne‐functionalized silica nanoparticles are coupled directly with azide‐modified polymers by ‘click chemistry’ to yield organic–inorganic hybrid nanomaterials.

     

Modular Synthesis of Thermosensitive P(NIPAAm‐co‐HEMA)/β‐CD Based Hydrogels via Click Chemistry

Two kinds of representative polymers, poly(N‐isopropylacrylamide) (PNIPAAm) and β‐cyclodextrin (β‐CD) were selected and modified with azide and alkyne fucntional groups, respectively. When the solutions of these two modified polymers were mixed together, a cross‐linking reaction, a type of Huisgen's 1,3‐dipolar azide‐alkyne cycloaddition, occurred in the presence of Cu(I) catalyst. The strategy described here provides several advantages for the hydrogel formation including mild reaction conditions and controllable gelation rate. The resulted hydrogels were studied in terms of scanning electric microscopy (SEM), equilibrium swelling ratio and swelling/shrinking kinetics. The data obtained demonstrated the hydrogels had a porous structure as well as favorable thermosensitivity.

     

Ring‐Opening Polymerization of ε‐Caprolactone by Poly(ethylene glycol) by an Activated Monomer Mechanism

Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et₂O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.

The non‐metal catalyzed living ring‐opening polymerisation of ε‐caprolactone by PEG.     

Fabrication of Au/Titania Composite Nanodot Arrays from Au‐Loaded Block Copolymer Micellar Films

Summary: A simple route to an ordered array of metal/semiconductor oxide composite nanodots is presented. Micellar monolayer films of polystyrene‐block‐poly(2‐vinyl pyridine) (PS‐b‐P2VP) loaded with HAuCl₄ in the P2VP nanodomains are used as templates. TiO₂ is generated selectively within the polar P2VP domains of PS‐b‐P2VP/HAuCl₄ films by chemical vapor deposition of TiCl₄. Subsequent removal of the organic matrix by oxygen plasma or UV light leads to an array of Au/TiO₂ composite nanoparticles on the substrate surface.

Schematic illustration of the process to fabricate an array of Au/titania composite nanodots.     

Single‐Chain‐Particles of Poly(N‐isopropylacrylamide)

Spherical single‐chain‐particles of poly(N‐isopropylacrylamide) were prepared in aqueous solution above the lower critical solution temperature upon the addition of sodium dodecyl sulfate. The size of the single‐chain‐particles was investigated by means of transmission electron microscopy and viscosity measurements of the corresponding solutions, indicating the absence of inter‐chain entanglements among the single‐chain‐particles.

Schematic of the preparation of PNIPAM single‐chain‐globules in solution.     

“Sandglass”‐Shaped Self‐Assembly of Coil–rod–coil Triblock Copolymer Containing Rigid Aniline‐Pentamer

The amphiphilic PEG_{1 500}‐b‐EM AP‐b‐PEG_{1 500} (EM PAP) triblock copolymer of poly(ethylene glycol) (PEG) and emeraldine aniline‐pentamer (EM AP) in its concentrated solution can self‐assemble into a special shape like “sandglass”, as observed by transmission electron microscopy (TEM), field emission scanning electron microscopy (ESEM) and atomic force microscopy (AFM). This “sandglass”‐shaped assembly is composed of several “rods” aggregated in the middle, with every “rod” being about 8 µm in length and 300 nm in diameter. We conclude that the special “sandglass”‐shaped assembly may come into being because of the inducement effect of the crystallization of EM AP segments, by studying electron diffraction (ED) results and wide‐angle X‐ray diffusion (WAXD) characterization of the EM PAP triblock copolymer.

     

3‐Ethylated N‐Vinyl‐2‐pyrrolidone with LCST Properties in Water

The monomer 3‐ethyl‐1‐vinyl‐2‐pyrrolidone ( 3 ) and the homopolymer poly(3‐ethyl‐1‐vinyl‐2‐pyrrolidone) ( 5 ) have been synthesized. Polymer 5 is soluble in water and shows a critical temperature (T_c) of 27 °C. The presence of cyclodextrin causes a slight shift of the T_c. The lower critical solution temperature (LCST) could be varied between 27 and 40 °C by copolymerization with N‐vinyl‐2‐pyrrolidone. A linear correlation between the T_c and the copolymer composition is observed.

     

Temperature‐Responsive Graft Copolymers with Poly(propylene glycol) Side Chains

The phase behavior of graft copolymers in aqueous solution was investigated. The graft copolymers consist of poly(propylene glycol) (PPG) side chains and N,N‐dimethylacrylamide (dMA), N‐vinylimidazole (VIm), and N‐isopropylacrylamide (iPA), respectively, as backbones. Phase transition temperatures of the PPG copolymers increased with increasing the content of dMA and iPA as relatively more hydrophilic comonomers and with an increase in the degree of ionization of the incorporated VIm units.

Chemical structure of the graft copolymers