Summary: A series of high clay content Laponite XLS/polyacrylamide (PAAm) nanocomposite hydrogels (S‐M gels) with excellent resilience, low elastic hysteresis, and ultrahigh elongation, have been successfully synthesized. Based on our results, it is concluded that the mechanical properties of nanocomposite hydrogels probably depend to a great extent on the hydrophilicity and flexibility of the macromolecules. Moreover, it is found that the transparency during the in‐situ polymerization of S‐M gels does not change, which is quite different from clay/poly(N‐isopropylacrylamide) nanocomposite hydrogels.
Formation of nanocomposite hydrogels using Clay‐S by in‐situ polymerization. 相似文献
New multifunctional copoly(2‐oxazoline) nanoparticles were prepared for cell studies. The polymer contains double‐bond side chains as potential reaction sites for “thio”‐click reactions as well as a fluorescein label covalently bound to the polymer backbone. Using the nanoprecipitation technique, spherical nanoparticles of 200–800 nm were obtained. Confocal laser scanning microscopy measurements revealed the cellular uptake of the nanoparticles.
Sixteen parallel polymerization reactions of 2‐ethyl‐2‐oxazoline have been performed at different temperatures in an automated synthesizer that allowed individual heating of each reactor. During the reactions samples were taken automatically, which were characterized by means of both online GPC and offline GC, in order to optimize the reaction temperature and to determine the activation energy of the polymerization.
The coating of super‐paramagnetic iron oxide nanoparticles (SPIONs) with multiple shells is demonstrated by building a layer assembled from carboxymethyldextran and poly(diallydimethylammonium chloride). Three shells are produced stepwise around aggregates of SPIONs by the formation of a polyelectrolyte complex. A growing particle size from 96 to 327 nm and a zeta potential in the range of +39 to ?51 mV are measured. Microscopic techniques such as TEM, SEM, and AFM exemplify the core‐shell structures. Magnetic force microscopy and vibrating sample magnetometer measurements confirm the architecture of the multishell particles. Cell culture experiments show that even nanoparticles with three shells are still taken up by cells.
Novel poly(2‐(3‐sulfo)benzoyl‐1,4‐phenylene)‐block‐polynaphthalimide (PSP‐b‐PI) copolymers were successfully synthesized by Ni(0)‐catalyzed copolymerization of 2,5‐dichloro‐3′‐sulfo‐benzophenone and dichloro‐terminated naphthalimide oligomer. The membranes exhibited a microphase‐separated structure and good hydrolytic stability at 130 °C. They showed a fairly strong anisotropy of membrane swelling with much smaller in‐plane swelling, but a rather weak anisotropy of proton conductivity. The membranes had a fairly high through‐plane conductivity in water and even under low relative humidity. The PSP‐b‐PI copolymer with an IEC of 1.5 meq · g−1 showed high PEFC performance due to the high through‐plane conductivity.
A facile method for preparing gold nanoparticle (AuNP) films with a high loading density based on the seed‐mediated growth of AuNPs on a polyelectrolyte multilayer (PEM) is reported. Use of PEMs as a base layer for gold seed adsorption confers controllability on the loading density of the AuNP film and size of the resulting AuNPs. In addition, the shape of the final AuNPs could be varied by adapting various species of polyelectrolytes. The optical response of the AuNP films is stable, because of the relatively uniform distribution of the AuNPs over a large area. The AuNP film has been used as a substrate for surface‐enhanced Raman scattering (SERS), and it shows stable and reproducible enhancement in the range from 105 to 107 depending on the fabrication condition.
A directed diffusion approach is used to create atomistic models of crosslinked epoxy. In polymerization‐based approaches for preparing epoxy model structures, conversions higher than 95% are difficult to achieve due to very slow diffusion of unreacted monomers and crosslinkers in the partially formed network. This problem is overcome by creating very long bonds in the polymerization stage, and then relaxing these to equilibrium values by using a directed‐diffusion‐based relaxation strategy. The method minimizes the use of custom code by relying on the in‐built functionality in LAMMPS package (S. Plimpton, J. Comput. Phys. 1995 , 117, 1). The approach allows for near‐complete conversion (≈99%) and the thermal and volumetric properties of the structures so prepared show good agreement with experimental data.
Polymer nanocomposites continue to receive considerable attention as multifunctional hybrid materials, with most nanocomposites fabricated by physical dispersion of surface‐functionalized nanoscale objects. In this study, we explore the viability of growing Pd‐containing nanoparticles from Na2PdCl4 in two different polymers: hypercrosslinked polystyrene (HPS) and an aromatic polyimide (PIm). In HPS, single Pd‐containing nanoparticles possessing a relatively narrow size distribution (ca. 1–4 nm) form upon reduction of the divalent PdCl ions. Single nanoparticles with a broad size distribution ranging from ≈2 to 16 nm develop in PIm, which simultaneously undergoes chemical crosslinking during ion reduction. Such hybrid materials hold promise in molecular catalysis and gas separation.
This review article describes the preparation of polymer brushes by nitroxide‐mediated radical polymerization using either the ‘grafting to’ or the ‘grafting from’ approach. The use of TEMPO as a classical initiator is intensively described. More sophisticated nitroxides are also included in the discussion. Brush formation on flat surfaces such as wafers and also on particles is reported. Finally, some applications of polymer brushes are presented.
The mathematical treatment of polymer modification systems, described by population balances containing convolution is discussed. The two‐dimensional case (molecular weight vs. number of branch points) was considered by utilizing approximations of distributions, expanding them in terms of Gaussian basis functions. Three branching reactions were addressed: chain backbone to chain end point coupling; three‐functional coupling of chain ends; and crosslinking. The results were compared to those of Monte Carlo (MC) simulations. Good agreement was observed, although the quality of a distribution as generated by the numerical approach is much better in view of the strong scatter in the MC data.
Summary: Thermogravimetry and differential scanning calorimetry have been used to study the thermal and thermo‐oxidative degradation of polystyrene (PS) and a PS–clay nanocomposite. An advanced isoconversional method has been applied for kinetic analysis. Introduction of the clay phase increases the activation energy and affects the total heat of degradation, which suggests a change in the reaction mechanism. The obtained kinetic data permit a comparative assessment of the fire resistance of the studied materials.
The change in activation energy for the degradation of PS and the PS–clay nanocomposite with the extent of polymer conversion. 相似文献
Stable nanoparticle vesicles were for the first time prepared from adamantyl‐ and cyclodextrin (CD)‐modified silica nanoparticles forming host–guest interactions in aqueous solution. Adamantyl‐functionalized nanoparticles were obtained from thiol‐isocyanate reaction of thiol‐modified nanoparticles with 1‐adamantyl isocyanate. The CD modified silica particles were isolated from a reaction of mono‐6‐para‐toluenesulfonyl‐β‐cyclodextrin with the thiol functionalized silica under microwave conditions in basic media. The obtained particles were characterized in respect of agglomeration and self‐assembly behavior in aqueous solution by dynamic light scattering and transmission electron microscopy. The found vesicle structures are exceptionally stable even after evaporation of water. Such inorganic hollow spheres formed through self‐assembly processes may be important for chemical storage and transport. The technique of chemically‐driven assembly is an attractive option to form useful complex structures by tunable agglomeration.
A natural and synthetic layered silicate (LS) was modified with trihexyltetradecyl‐phosphonium tetrafluoroborate (an ionic liquid) via a cationic exchange reacation. The exchange reaction and loading of modifier was investigated using a combination of WAXD, inductively coupled plasma‐optical emmission spectroscopy (ICP‐OES) and thermogravimetric analysis (TGA). The thermal stability of the modified LS was enhanced by up to 150 °C, when compared with conventional quaternary ammonium cations, making melt mixing of such modified nanoclays possible with poly(ethylene‐terephthalate) (PET).
The functionalization of magnetite (Fe3O4) nanoparticles with dopamine‐derived clickable biomimetic anchors is reported. Herein, an alkyne‐modified catechol‐derivative is employed as the anchor, as i) the catechol‐functional anchor groups possess irreversible covalent binding affinity to Fe3O4 nanoparticles, and ii) the alkyne terminus enables further functionalization of the nanoparticles by the grafting‐onto approach with various possibilities offered by ‘click’ chemistry. In the present work, azido‐end group functionalized Rhodamine and poly(ethylene glycol) (PEG) are utilized to coat the iron oxide nanoparticles to make them fluorescent and water soluble.
A precise control of metallic‐nanoparticle assembly is highly critical for the realization of tangible, high‐performance devices or materials. Until recently, nanoparticle assembly using 1D templates had been limited to a narrow spectrum of nanoparticles as it was mostly dependent on the surface chemistry of the nanoparticles used. Inspired by the universal adhesive properties of mussels, we demonstrate a universal polymeric template for 1D assembly of various nanoparticles including, gold nanoparticles, iron oxide nanoparticles, and quantum dots. We find that the length of the 1D assembly is tunable using hyaluronic acid‐graft‐catechol templates with various contour lengths.
Porous surface patterns are used in a wide variety of practical applications. Honeycomb‐patterned porous polymer films are good templates for preparing porous surfaces due to their simple fabrication and the arrangement of pores on the surface. Catechol groups include in adhesive protein of mussels have attracted much attention due to their highly and substrate‐independent adhesive properties. In this paper, highly and substrate‐independent adhesive honeycomb‐patterned porous polymer films are prepared by using amphiphilic copolymer having catechol moieties. Furthermore, porous surface patterns are transferred on various organic or inorganic substrates by wet etching with using adhesive honeycomb films as templates.
Some new water‐soluble bis‐porphyrins, constituted of two porphyrin units spaced by means of aliphatic bridges of different lengths, were synthesized and characterized by MALDI‐TOF mass spectrometry, 1H NMR and UV‐vis spectroscopy. The hydrosolubility of these uncharged compounds was guaranteed from the presence of six long PEG chains bound on the peripheral positions of the two porphyrins. Cobalt and zinc derivatives were also prepared. In the case of Co‐bis‐porphyrin, the appearance of induced circular dichroism (ICD) signals in water solution confirmed the formation of stable complexes with some amino acids, in which the bis‐porphyrin behaves like molecular tweezers.
Gold nanoparticles (AuNP) with carboxyl groups on their surface were used in combination with PAH for the layer‐by‐layer coating of CaCO3 microparticles, followed by the dissolution of the CaCO3 core. SEM, TEM, and confocal microscopy are used to characterize the hybrid nanoparticles/polyelectrolyte capsules. As the AuNP have carboxyl groups on their surface, their charge density is pH dependent; therefore, the capsules exhibit a pH‐dependent swelling and can be deconstructed both at low and high pH. By covalent cross‐linking of the carboxyl groups of the AuNP and the amino groups of the PAH, it is possible to suppress the pH‐responsive behavior. AuNP are used as activation centers using IR light and this ability is used to release encapsulated material from the nanoparticles/polyelectrolyte capsules as well as for the enhancement of detection and imaging of such capsules by Raman microspectrosopy.
