Polymer translocation through a narrow pore is investigated using a particle‐based dissipative particle dynamics (DPD) method. A rigid core is included in each particle to avoid particle interpenetration problems based on the original DPD method. Electrostatic interactions of charged particles are simply represented via screened Coulombic interactions. The average translocation time τ versus polymer length N satisfies the scaling law τ ∼ Nβ. The scaling exponent β depends on solvent quality. The results demonstrate that solvent quality exerts a considerable influence on the dynamics of translocation of polymers. The findings may help facilitate understanding of the dynamic behaviors of various polymer and DNA molecules during translocation processes.
The ability to control the dispersion of carbon nanotubes in polymers is key to most applications of nanotube‐polymer composites. This feature article describes recent advances in methods used to disperse carbon nanotubes and considers how these methods affect dispersion on different length scales. It is becoming increasing clear that perfect dispersion is not desired for many applications, in particular for electrical conductivity, and controlling the dispersion is key for proper function of the composite in its intended application.
The layer‐by‐layer (LBL) assembly of poly(diallyldimethylammonium chloride) and poly(sodium styrene sulfonate) on poly(sulfo propyl methacrylate) brushes resulted in films with nanometer‐ and micrometer‐sized holes and ledges, observed by atomic force microscopy and scanning electron microscopy. Polyelectrolyte assembly was followed by the quartz microbalance technique. The formation of ledges and holes is explained by the interaction of the brush polymers with the incoming polyelectrolytes during the LBL assembly, inducing a spatially localized and self‐organized accumulation of the assembled polymers.
The synthesis of a new glycomonomer based on mannose, prepared via CuAAC, is reported. The resulting 1,2,3‐triazole linkage between mannose and the polymer backbone ensures the formation of highly stable glycopolymers, which will not undergo hydrolysis. The monomer 2′‐(4‐vinyl‐[1,2,3]‐triazol‐1‐yl)ethyl‐O‐α‐D ‐mannopyranoside was polymerized in the presence of a RAFT agent – 3‐benzylsulfanylthiocarbonylsulfanyl propionic acid – to yield well‐defined polymers with molecular weights up to 51 500 g mol?1 and a PDI of 1.16. The resulting polymer was employed as a macroRAFT agent in the polymerization of NIPAAm in order to generate thermo‐responsive block copolymers, which undergo reversible micelle formation at elevated temperatures. The rapid interaction between the polymers prepared and ConA confirms the high affinity of these structures to proteins. While the linear glycopolymers already undergo a fast complexation with ConA, the reported rates have found to be exceeded by the micellar glycopolymer structure presented in the current contribution.
Summary: Linear polymeric core, polyethylenimine (PEI), is successfully dendronized divergently using different‐generation polyamidoamine (PAMAM)‐type dendrons. The formed dendronized polymers are further end‐capped using long alkyl acrylate, hexyl acrylate, to give macromolecular amphiphiles, which perform as unimolecular nanocontainers, capable of encapsulating water‐soluble dye in their interiors. The encapsulation properties are found to be generation‐dependent, in which, at higher generations of nanocontainers, the cavity becomes more localized, due to dense packing of the dendrons at their termini.
Dendronization of a linear polymeric core followed by capping with hydrophobic arms. 相似文献
Twin polymerization is a novel technique for synthesizing hybrid polymers with domain sizes in the nanometer range. While a broad variety of monomers have been investigated, the mechanistic details and the most important influences on the nanostructure formation are unknown. A scale bridging approach is presented to simulate the twin polymerization of 2,2'‐spirobi[4H‐1,3,2‐benzodioxasiline]. This approach is based on detailed quantum chemical calculations that yield insight into reactivity and structure at the molecular level while the kinetics of the network formation process and the influences that govern structure formation are investigated at the mesoscopic level by a coarse‐grained simulation.
Living cationic ring‐opening polymerizations of 2‐ethyl‐2‐oxazoline and purification of the resulting polymers were performed utilizing an automated synthesizer. Eight polymers (500 mg scale) as well as 40 polymers (150 mg scale) were synthesized in parallel to investigate the reproducibility and the living character of the polymerizations. The poly(2‐ethyl‐2‐oxazoline)s obtained such were characterized by means of 1H NMR spectroscopy, MALDI‐TOF mass spectrometry and online gel permeation chromatography.
Strong electrolyte temperature‐sensitive hydrogels were synthesized by radiation polymerization using N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methylpropanesulfonate. The influence of irradiation dose and mole ratio of the monomers was examined by swelling measurements in aqueous solution and organic solvents. The hydrogels without any pollution were applied in concentrating protein.
Effect of irradiation dose on swelling ratios of P(NIPA‐co‐NaAMPS) hydrogels. 相似文献
A close correllation between molecular‐level interactions and macroscopic characteristics of polymer networks exists. The characteristics of the polymeric hydrogels assembled from β‐cyclodextrin (β‐CD) and adamantyl (AD) substituted poly(acrylate)s can be tailored through selective host–guest complexation between β‐CD and AD substituents and their tethers. Dominantly, steric effects and competitive intra‐ and intermolecular host–guest complexation are found to control poly(acrylate) isomeric inter‐strand linkage in polymer network formation. This understanding of the factors involved in polymeric hydrogel formation points the way towards the construction of increasingly sophisticated biocompatible materials.
A group of ferrocene‐containing polymers were synthesized from vinylferrocene, ethynylferrocene and 1,1′‐dibromoferrocene, and properties of the formed polymers were examined to clarify their potential as a new class of cathode‐active, charge‐storage materials for rechargeable batteries. Vinylferrocene polymerized with 2,2′‐azoisobutyronitrile (AIBN) to give a polymer with number‐average molecular weights of 2 200–5 100 g · mol−1 in 12–41% yields, while ethynylferrocene and 1,1′‐dibromoferrocene polymerized with Rh catalysts and by step‐growth mechanism, respectively, to provide insoluble polymers in 71–96% yields. The capacities of organometallic rechargeable cells fabricated with poly(vinylferrocene), poly(ethynylferrocene), and poly(ferrocene) reached 105, 105, and 95 Ah · kg−1, respectively. In particular, poly(vinylferrocene) displayed completely reversible charge/discharge processes featuring a constant voltage of around 3.5 V.
Two kinds of cyclodextrin/peptide (CD/peptide) hybrids bearing ZnII‐cyclen or cyclen, dansyl and β‐cyclodextrin (β‐CD) units have been synthesized as chemosensors for organic anionic molecules. ZnII‐cyclen serves as a ligand site and β‐CD is a receptor site for guest molecules, while the dansyl unit acts as a fluorescent probe. Examination of the fluorescence behaviors of these CD/peptides suggest that the hybrid containing Zn2+ has larger binding constants with respect to anionic molecules than that without Zn2+.
A nickel α‐diimine catalyst was used for Grignard metathesis (GRIM) polymerization of 2,5‐dibromo 3‐hexylthiophene and 2‐bromo‐5‐iodo‐3‐hexylthiophene monomers. GRIM polymerization of 2‐bromo‐5‐iodo‐3‐hexylthiophene generated regioregular polymers with molecular weights ranging from 3 000 to 12 000 g · mol−1. The nickel α‐diimine catalyst was also successfully used for the GRIM polymerization of a bulky benzodithiophene monomer.
Summary: The use of electrostatically addressable templates for the directed assembly of conducting polymers and pattern transfer to another polymer substrate is demonstrated. Doped conducting polyaniline was selectively assembled on the patterned template assisted by a DC electric field. Adding an insulated silicon dioxide layer onto the surface of the silicon wafer is critical to the formation of patterned PANi rather than a PANi film. After deposition, it was demonstrated that by compression molding or solution casting methods, patterned PANi can be completely transferred to a secondary polymer substrate, such as an NBR sheet or a polyurethane film. The conductivity of PANi lines on the PU film was found to be as high as 0.87 S · cm−1. The simple one‐step assembly process for patterning conductive polymers and transfer provides a promising nanomanufacturing approach for cost‐effective and high performance flexible nanoelectronics and biosensors.
Optical image of PANi‐assembled templates with patterned gold lines connected to negative electrodes at 10 V for 1 min. 相似文献
We have developed a novel strategy for the preparation of ion‐bonded supramolecular star polymers by RAFT polymerization. An ion‐bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert‐butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by 1H NMR and GPC. The results show that the polymerization possesses the character of living free‐radical polymerization and the ion‐bonded supramolecular star polymers PSt, PtBA, and PSt‐b‐PtBA, with six well‐defined arms, were successfully synthesized.
In this work, we report the design of a new multi‐functional, water‐soluble conjugated polymer integrating both a DNA intercalator and a redox label. Based on this multi‐functional conjugated polymer, we develop a sequence‐specific electrochemical DNA sensor, where the acridine unit serves as the basis for sequence discrimination, and the ferrocene label provides the electrochemical signal. Moreover, the conjugated polythiophene helps transfer electrons from ferrocene to the electrode. This sensor provides a new way for rapid and convenient detection of DNA targets.
A novel method for synthesis of ultrafine polymeric nanoparticles of diameters less than 20 nm has been developed. The method is based on miniemulsion polymerization exploiting combination of the in situ surfactant generation approach (whereby the surfactant is formed at the oil–water interface by reaction between an organic acid and a base) and ultrasonication. Conventional radical polymerization and nitroxide‐mediated radical polymerization of styrene have been conducted in miniemulsion using oleic acid/potassium hydroxide, demonstrating that particles with diameters less than 20 nm can be obtained by this approach at surfactant contents much lower than traditionally required in microemulsion polymerizations.
In this communication, β‐cyclodextrin modified quantum dots were used as a water‐soluble “supramolecular” cross‐linker (SCL) because of its surface's supramolecular activity. The guest monomer‐loaded SCL (mSCL) can be used to copolymerize with water‐soluble monomers leading to transparent hybrid supramolecular hydrogels. This simple and versatile method opens new venues for the preparation of hybrid supramolecular hydrogels and the host–guest chemistry of cyclodextrins.
Summary: Thermosensitive polymer nanotubes can be fabricated within an aminopropylsilane‐modified porous anodic aluminum oxide membrane by surface‐initiated atom transfer radical polymerization (ATRP) followed by template removal. DSC experiments prove that the synthesized PNIPAM‐co‐MBAA copolymer nanotubes have a reversible thermosensitive behavior. The temperature‐induced changes in dimension and shape of the nanotubes were studied by AFM in real time in an aqueous environment. It indicates that the nanotubes undergo a shape alteration from an “ellipse” to “circular” shape in water upon heating to LCST or above.
PS grafted silica nanoparticles have been prepared by a tandem process that simultaneously employs RAFT polymerization and click chemistry. In a single pot procedure, azide‐modified silica, an alkyne functionalized RAFT agent and styrene are combined to produce the desired product. As deduced by thermal gravimetric and elemental analysis, the grafting density of PS on the silica in the tandem process is intermediate between analogous “grafting to” and “grafting from” techniques for preparing PS brushes on silica. Relative rates of RAFT polymerization and click reaction can be altered to control grafting density.
Highly functional and monodisperse macromolecules with tailored architecture constitute the key to designing efficient and smart nanomaterials. Dendrimers offer real potential to achieve this goal, and one of the earlier challenges faced by this novel class of polymers has been addressed by the evolution of synthetic methodologies. This review provides an evaluation of the role played by chemistry in taking these macromolecules of academic relevance to practical industrial and biological applications, in a relatively short period. One can now construct dendrimers in a ‘made‐to‐order’ fashion, for numerous applications in a variety of disciplines.
