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.
This paper focuses on the attachment of densely grafted polymer layers (polymer brushes) to various inorganic and polymeric substrates by the “grafting to” method. A brief overview of synthesis of polymer brushes by the method is first provided, with emphasis on chemical approaches to polymer attachment. The second part of the paper covers the synthesis of polymer layers via a recently developed macromolecular anchoring layer approach. Several examples of application of the grafting technique are presented for generation of hydrophobic, hydrophilic, gradient, and switchable surfaces.
A conceptual model is proposed for the viscoelastic response of dilute polymer solutions containing well‐dispersed low volume fraction spherical particles. The equilibrium structure of the reversibly adsorbed polymer layer on the particle surface was characterized by a scaling theory. The dynamics of the polymer chains were studied by a Maxwell type kinetic model. At the limit of small particle size, our results show that the monomer‐filler energetic affinity, particle volume fraction and surface friction strongly affect the overall viscoelastic response of the filled solutions and lead to unusual viscoelastic properties that have been observed experimentally. These properties include a dramatic increase in shear viscosity, intense shear thinning, and solid‐like behavior at low frequency domains.
The united atoms (UA) and dummy hydrogen atom (DHA) approaches for molecular dynamics simulations of the interface between oxidized atactic polystyrene (aPS) thin films and water are compared. For both oxidized and non‐oxidized aPS films the polymer density profile decays steepest when using the UA model. The surface roughness of the aPS film and the ordering of the phenyl rings near the surface decrease upon changing from vacuum to water for the UA, but not for the DHA model. This also supports the fact that the non‐oxidized aPS films modeled in DHA representation become less hydrophobic. The water structure close to the interface also suggests that the aPS films modeled using UA are more hydrophobic compared to the aPS films modeled with DHA in the phenyl rings.
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.
A novel semi‐interpenetrating polymer network based on alginate and poly(N‐isopropylacrylamide) (PNiPAAm) has been synthesized that shows response to temperature and magnetic fields. Highly homogeneous porous hydrogels are obtained by copolymerizing N‐isopropylacrylamide and bis‐acrylamide in the presence of an aqueous alginate solution. The synthesis of magnetic iron oxides by in‐situ oxidation of iron cations coordinated to the alginate network results in a hydrogel with an enhanced deswelling rate with respect to pure PNiPAAm.
In this study, the hydrophobic liquid template method was firstly used to prepare temperature sensitive, porous poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel. During the radical polymerization, hydrophobic polydimethylsiloxane (PDMS) and surfactant sodium dodecyl sulfate (SDS) were used as liquid templates and stabilizer, respectively. After removal of the liquid templates, porous PNIPAAm hydrogel was obtained. This gel exhibited superfast shrinking properties when being transferred from below to above the lower critical solution temperature (LCST), which was ascribed to the interconnected porous structures.
A dextran‐based dual‐sensitive polymer is employed to endow gold nanoparticles with stability and pH‐ and temperature‐sensitivity. The dual‐sensitive polymer is prepared by RAFT polymerization of N‐isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder‐form. UV and DLS measurements confirm that the temperature‐induced optical changes and aggregation behaviors of the particles are strongly dependent on pH.
Summary: The impact of a droplet on a solid surface, pre‐patterned with a barrier, was studied using a diffuse interface model. The effect of the wettability of the barrier material and the width of the barrier on droplet spreading was investigated. The results show that depending on the barrier wettability and width, the flow of the spreading droplet can be controlled and that the droplet may or may not overflow the barrier.
Droplet shapes with the corresponding velocity field for different barrier contact angles at ± = 1.5. 相似文献
Summary: The synthesis of a hyperbranched polymer containing a rhenium bipyridine complex is reported. The polymer was synthesized from a monomer that contains two chlorotricarbonyl rhenium(I ) bipyridine moieties and a stilbazole ligand, and the polymer was formed by the coordination reaction in one single step. Gel permeation chromatography results showed that the resulting polymer had a strong interaction with the column packing material, which was reduced when the eluent was added with an electrolyte. Both atomic force microscopy and laser light scattering showed that the size of the polymer molecules was in the range between 25–30 nm. A monolayer of polymer molecules could form on a pretreated substrate by the self‐assembly process, which can serve as the building block for multilayer ultrathin film devices.
The metal‐containing hyperbranched polymer synthesized here. 相似文献
Kinetic modeling is used to obtain insight in the complex interplay between reaction rates and obtained polymer properties in the SG1 and the TEMPO mediated bulk polymerization of styrene at 396 K. The increase of the viscosity during NMP is accounted for. At higher targeted chain lengths, chain transfer to dimer and transfer from nitroxide to dimer are shown to cause the experimentally observed reduced control over the average polymer properties and to result in a clear fronting of the polymer chain length distribution. The potential of kinetic modeling to design tailor‐made synthesis strategies is illustrated. Simulations indicate that careful control of the polymerization conditions allows to obtain an important improvement of the polymer properties. The approach is also applicable for NMP mediated by other alkoxyamines/nitroxides and allows to expand the application range of NMP for styrene polymerization in particular to synthesize complex polymer architectures by assembly of functionalized polymers.
Summary: We propose a new approach for predicting polymer properties from structured molecular representations based on recursive neural networks. To this aim, a structured representation is designed for the modeling of polymer structures. This representation can also account for average macromolecule characteristics. Preliminarily, this model is applied to the calculation of the Tg of (meth)acrylic polymers with different stereoregularity.
Representation of poly(methyl methacrylate) as a chemical tree and unfolding of the encoding process through its structure. 相似文献
A pathway for marking of polymer chains with radical spin traps during pulsed laser polymerization in free radical polymerization is presented. By introducing a so‐called marker that forms a non‐propagating radical at (or shortly after) the incidence of a laser pulse, a polymer subdistribution is generated by specifically terminating propagating radicals via combination with such a marker radical. The generated polymer subdistribution can subsequently be imaged by modern soft‐ionization mass spectrometry. Herein, the general methodology of the method in which such marker is generated via reaction of an initiating radical with a nitrone is demonstrated on the examples of BA and VAc.
Summary: A simple method to prepare surfactant‐free and solvent‐free semiconducting polymer particles by using an environmentally benign supercritical carbon dioxide (scCO2) process is reported. The process of the rapid expansion of supercritical solutions (RESS) is used to produce spherical particles of poly[2‐(3‐thienyl)acetyl 3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctanoate] (PSFTE), 50–500 nm in size, from 0.1–0.5 wt.‐% PSFTE solutions in CO2 at pre‐expansion temperatures of 40 °C and pre‐expansion pressures of 276 bar.
An FESEM image of PSFTE particles produced by the RESS process with CO2. 相似文献
A new route consisting of simultaneous centrifugal spinning and solution blowing to form polymer nanofibers is reported. The fiber diameter (60–1000 nm) is shown to be a function of polymer concentration, rotational speed, and working pressure of the processing system. The fiber length is dependent on the rotational speed. The process can deliver 6 kg of fiber per hour and therefore offers mass production capabilities compared with other established polymer nanofiber generation methods such as electrospinning, centrifugal spinning, and blowing.
We describe an enzyme‐responsive polymeric vehicle, which is of great interest in controlled drug delivery, biosensing, and other related areas. The polymer synthesized using lipase as catalyst in DMSO has a favorable molecular structure that is quickly hydrolyzed by lipase in aqueous phase, and allows a fast release of encapsulated molecules.
Transparent film materials with excellent mechanical and thermal properties were elaborated by drying a latex suspension of armored polymer/Laponite composite particles. Low‐temperature TEM observation of ultrathin cross‐sections of the films indicated a unique network morphology characterized by a “honeycomb” distribution of the Laponite platelets remindful of the original particles morphology.
A novel two step method has been developed for the preparation of anisotropic polymer particles using soap‐free emulsion polymerization in the presence of the reactive silane coupling agent 3‐methacryloxypropyltrimethoxysilane (MPTMS). In the first step, seed polymer particles were prepared in the presence of MPTMS in water. In the second step, another polymerization was conducted in the presence of the seed particles, which induced anisotropic protrusion of polymer from the seed particles. The two step method is applicable to the preparation of anisotropic polymer particles containing inorganic particles such as silica. Silica particles inside the anisotropic polymer particles were dissolved with hydrofluoric acid, which created hollow polymer particles with anisotropy.
Summary: Poly(dimethylsiloxane) (PDMS) star polymers having a nanosized silica particle as a core were prepared by reacting silica nanoparticles with monoglycidylether‐terminated poly(dimethylsiloxane). This star polymer was a hybrid material having an extremely high content of silica. The PDMS arms formed an organic domain to separate the silica particles and to prevent particle aggregation. The star polymers exhibited good thermal stability and high activation energy of their degradation reaction, in comparison to the linear PDMS polymer and the PDMS/silica blending materials. This star polymer can be used as a flame retardant for polymeric materials and this preparation technique can be applied to prepare other star polymers.
An SEM image of poly(dimethylsiloxane) star polymers having nanosized silica particles as a core. 相似文献
