Poly(L ‐lactide)/layered aluminosilicate nanocomposites were synthesized in bulk by ring‐opening polymerization in the presence of two organo‐modified montmorillonites. When the organo‐modifier consisted of an ammonium cation bearing primary hydroxyl groups, polymerization was initiated by the alcohol functions after adequate activation. The growing polymer chains were directly “grafted” onto the clay surface through the hydroxyl‐functionalized ammonium cations yielding exfoliated nanocomposites with enhanced thermal stability.
TEM image of a fully exfoliated Cloisite®30B‐based nanocomposite, showing delamination of the silicate layers. 相似文献
Grafted conjugated polyelectrolytes were synthesized for the first time and characterized. The polymers demonstrated properties of a convenient and efficient protocol for creating Hg2+ sensors. The unique character of the new material comes from an anionic counterion nature with no external cofactors, and imparts high selectivity and fast detection for mercury ion in a fluorescence probe. The concept may be potentially applied to create new sensors for monitoring other ions.
The effect of various alkylaluminium compounds and their mixtures on ethylene polymerization catalyzed with a tridentate bis(imino)pyridinyliron catalyst is studied. Triethylaluminium and trihexylaluminium are good cocatalysts but yield polyethylenes with broad molar mass distribution (MMD) whereas triisobutylaluminium, a less efficient activator, gives polyethylenes with unimodal and narrow MMD. Specific mixtures of branched and linear alkylaluminium compounds yield highly active catalytic systems and polyethylenes with unimodal and tunable MMD.
SEC traces of PE prepared with iron catalyst and (1) TEA, (2) TiBA, and (3) THA (Al/Fe = 250) as cocatalysts. 相似文献
Photochromic spiropyran molecules were embedded in electrospun polymer microfibers. Electrospinning of a clear viscous chloroform solution containing a spiropyran and a matrix polymer, such as polystyrene and polyethylene oxide, affords polymer microfibers that are photoswitchable. Photomasked, 365 nm UV irradiation of the microfibers results in the generation of patterned color images owing to the selective transformation of the spiropyran molecules from their ring‐closed SP to ring‐opened MC form. The UV‐irradiated areas display brilliant red fluorescence, which changes to green fluorescence upon prolonged irradiation.
Small, organic, toxic compounds are not well eliminated by water‐treatment systems and eventually become concentrated in the human body. In this study, liposomes are employed to house aptamers with their own binding buffer. When small, organic, toxic compounds in water pass through a liposome barrier, only the target molecules are captured by the DNA aptamers inside the liposomes. The capture efficiency is not high when DNA aptamers are used in tap water. When DNA aptamers in liposomes are used, the capture efficiency increases more than 80%. The simultaneous and selective elimination of target toxicants is successfully performed for tap‐water samples containing toxicant mixtures.
The synthesis and characterization of a soluble high molecular weight copolymer based on 4,8‐bis(1‐pentylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene and 2,1,3‐benzoxadiazole is presented. High efficiency organic photovoltaic (OPV) devices comprised of this polymer and phenyl‐C71‐butyric acid methyl ester (PC71BM) were fabricated by additive processing with 1‐chloronapthalene (CN). When the active layer is cast from pristine chlorobenzene (CB), power conversion efficiencies (PCEs) average 1.41%. Our best condition—using 2% chloronapthalene as a solvent additive in CB—results in an average PCE of 5.65%, with a champion efficiency of 6.05%.
Cross‐linked lyotropic liquid crystal (LLC) assemblies represent a new class of polymer materials for membrane applications. These materials are formed by the phase‐segregation and self‐assembly of polymerizable amphiphiles in water into condensed ordered ensembles that can be cross‐linked in situ with retention of microstructure. The resulting LLC polymer networks have ordered, nanometer‐scale aqueous and cross‐linked organic domains, which can be used to affect gas solubility and diffusivity through the polymer to help separate molecules via the solution–diffusion mechanism. The open aqueous domains can also be used for pore transport and size exclusion with resolution on the molecular size level. The use and application potential of cross‐linked LLC assemblies as gas separation membranes, selective vapor barrier materials, and water nanofiltration and desalination membranes are presented.
In this paper, an atomistic model for PI/SiO2 hybrid nanocomposites was designed for the investigation of physical properties of this material on the base of molecular dynamics simulations. The thermal properties of a reference pure PI matrix in the temperature range of 300–650 K were first investigated. The results for the CTE and the glass transition temperature showed good agreement with the experimental data. Then, the thermal expansion of the model of PI/silica composite material with different SiO2 fractions was investigated at normal conditions. The CTE of the composite model decreases with the increase in the SiO2 content in agreement with experimental studies. The results show a threshold for the SiO2 loading beyond which the material model exhibits ultra‐low thermal expansion.
Summary: Using molecular dynamics simulations, we determine the linear and nonlinear viscoelastic properties of a model polymer melt in the unentangled regime. Several approaches are compared for the computation of linear moduli and viscosity, including Green‐Kubo and nonequilibrium molecular dynamics (NEMD). An alternative approach, based on the use of the Rouse modes, is also discussed. This approach could be used to assess local viscoelastic properties in inhomogeneous systems. We also focus on the contributions of different interactions to the viscoelastic moduli and explain the microscopic mechanisms involved in the mechanical response of the melt to external solicitation.
This study reports a continuous prepartion of spherical or hemispherical polymer particles simply utilizing the phase separation in polymer blend films during the coating process. We took an advantage of the strong phase separation between a water‐soluble crystalline polymer as a matrix and hydrophobic polymers as minor components. We demonstrated the prepartion of water‐soluble polystyrene (PS) particles, nitrilotriacetic acid (NTA)‐functionalized PS particles for protein separation, and semiconducting poly(3‐hexylthiophene) (P3HT) particles. The sizes of the particles could be controlled by adjusting the film thickness and weight fraction of the minor component polymers in the blend film. It provides a simple facile way to prepare polymer particles in a continous process.
Summary: Dissipative particle dynamics simulation was performed to study the formation of multicompartment micelles from ABC star triblock copolymers in water. The study revealed some new morphologies that had not been observed before and also provided a direct visualization of the evolution of wormlike multicompartment micelles that follows the fusion process. Thus, this work provides molecular understanding of multicompartment micelles which will be useful for the future rational synthesis of novel micelles.
Multicompartment micelles formed from ABC star triblock copolymers in water by DPD simulations. 相似文献
Equilibrium P–V–T properties of randomly crosslinked amorphous polymer networks are modeled via molecular dynamics simulation for connectivity ratios between 1.0 and 1.5. The relation between connectivity ratio and network shrinkage is studied over a wide range of temperatures and pressures. The simulation results are compared to a mean‐field Flory–Huggins lattice model.
The RAFT radical polymerization of vinyl monomers in supercritical carbon dioxide was modeled using the Predici® simulation package. The sensitivity of polymerization responses on formulation and process variables was analyzed. The simulations were carried out using kinetic and physical parameters corresponding to the polymerization of methyl methacrylate in supercritical carbon dioxide, using AIBN as initiator, at 65 °C and 200 bar, and using values of the addition and fragmentation kinetic rate constants of a “typical” RAFT agent, as reference conditions. This is the first report in the literature addressing the modeling or simulation of RAFT polymerization in supercritical carbon dioxide.
Summary: Polystyrene (PS) micro‐ and nanospheres with uniform dimensions and smooth surfaces have been produced by electrospray. The effect of PS molecular weight on beads morphology and the fundamental role of concentration have been investigated. Moreover, a new apparatus was designed to collect the polymer spheres during the process and to prevent the coalescence among the spheres.
PS micro‐ and nanospheres produced by electrospray 相似文献
Here, we report the use of fluorescently labelled proteins to study protein adsorption to microarrayed synthetic polymers for the first time, indicating that this method is appropriate for the study of protein adsorption on these arrays. To investigate protein adhesion directly we use atomic force microscopy (AFM) to measure the force of adhesion between a protein‐coated probe and the arrayed polymers. Both approaches show promise as methods for screening protein interactions with polymers in a microarray format. Comparison of these very different measures of protein–surface interactions indicate a good correlation.
Functional three‐dimensional (3D) micropatterns of diacetylene supramolecules embedded in a host polymer have been successfully fabricated by a replica‐molding (REM) technique. Dimensional reduction as a result of liquid evaporation during the curing process does not affect the conformational features of the transferred patterns. Polymerization of the diacetylene vesicles using 254 nm UV‐light irradiation from the back‐side of the transparent substrate induces blue colored polydiacetylene (PDA) micro‐images. Interestingly, the polymerization selectively occurs in the molded areas because of the sub‐300 nm light blocking property of SU‐8. 3D fluorescence patterns are readily obtained by heat treatment of the blue images on the film.
