A novel amphiphilic diblock copolymer composed of a hydrophilic poly(ethylene oxide) block and a hydrophobic block copolymerized by azobenzene‐containing methacrylate and N‐isopropylacrylamide was synthesized using ATRP. The polymer micelles showed dual responsiveness to heat and light. The size of the micelles was dependent on temperature and the encapsulated substance in the hydrophobic cores was released during heating and cooling processes. The hydrophobicity of the micellar cores appeared as a reversible change in response to light with neither disruption of the micelles nor leakage of the encapsulated substance while H‐aggregation of the azobenzene moieties was detected.
Au nanoparticles (NPs) and polymer composite particles with phase‐separation structures were prepared based on phase separation structures. Au NPs were successfully synthesized in amphiphilic block‐copolymer micelles, and then composite particles were formed by a simple solvent evaporation process from Au NPs and polymer solution. The phase separated structures (Janus and Core‐shell) were controlled by changing the combination of polymers having differing hydrophobicity.
Summary: Fabrication of honeycomb‐patterned films from amphiphilic dendronized block copolymer (PEO113‐b‐PDMA82) by ‘on‐solid surface spreading’ and ‘on‐water spreading’ method is reported. Highly ordered honeycomb films with quasi‐horizontally paralleled double‐layered structure can be fabricated by the on‐solid surface spreading method. This work raises the possibility that such structures can be formed in amphiphilic dendronized block copolymers and extends the family of source materials.
Thiol‐responsive symmetric triblock copolymers having single disulfide linkages in the middle blocks (called mono‐cleavable block copolymers, ss‐ABP2) were synthesized by atom transfer radical polymerization in the presence of a disulfide‐labeled difunctional Br‐initiator. These brush‐like triblock copolymers consist of a hydrophobic polyacrylate block having pendent oligo(propylene oxide) and a hydrophilic polymethacrylate block having pendent oligo(ethylene oxide). Gel permeation chromatography and 1H NMR results confirmed the synthesis of well‐defined mono‐cleavable block copolymers and revealed that polymerizations were well controlled. Because of amphiphilic nature, these copolymers self‐assembled to form colloidally stable micelles above critical micellar concentration of 0.032 mg · mL−1. In response to reductive reactions, disulfides in thiol‐responsive micelles were cleaved. Atomic force microscopy and dynamic light scattering analysis suggested that the cleavage of disulfides caused dissociation of micelles to smaller‐sized assembled structures in water. Moreover, in a biomedical perspective, the mono‐cleavable block copolymer micelles are not cytotoxic and thus biocompatible.
A route has been developed to disperse metal‐containing phthalocyanine dyes in a non‐polar medium based on amphiphilic block copolymer micelles of poly[styrene‐block‐(4‐vinylpyridine)] (PS‐b‐P4VP) and poly[styrene‐block‐(acrylic acid)] (PS‐b‐PAA) copolymers. Polar P4VP and PAA efficiently encapsulate cobalt(II ), manganese(II ), and nickel(II ) phthalocyanine dyes by axial coordination of nitrogen and µ‐oxo bridged dimerization with the transition metals, respectively. Good dispersion of the dyes is confirmed by the linear enhancement of Q‐bands in UV–vis absorption spectra with dye concentration. A thin monolayered PS‐b‐P4VP micelle film that contained a nickel(II ) phthalocyanine dye which efficiently adsorbs a laser beam on a localized area to generate a local heat higher than the glass transition temperatures of both blocks. One‐dimensional laser writing on the dye‐containing film allows the fabrication of a few submicrometer wide line patterns in which the self‐assembled nanostructure of the block copolymer is modified by the directional heat arising from laser scanning.
The storage moduli, shear moduli and surface morphologies of poly(vinyl alcohol) (PVA) and alumina hybrid hydrogels were investigated. The storage moduli of hybrid hydrogels with higher alumina contents were found to be 1.5 times higher than those of PVA gels. This increase in modulus might be attributed to the cohesion of alumina to the PVA network.
SEM photograph of Al7 PVA/alumina hybrid hydrogel. The photograph was taken with a magnification of × 220. 相似文献
The synthesis of water soluble star‐block copolypeptides and their encapsulation properties are described. The star‐block copolypeptides, obtained by ring‐opening polymerization of amino acid N‐carboxyanhydrides, consist of a PEI core, a hydrophobic polyphenylalanine or polyleucine inner shell, and a negatively charged polyglutamate outer shell. The encapsulation study showed that these water soluble, amphiphilic star‐block copolypeptides could simultaneously encapsulate versatile compounds ranging from hydrophobic to anionic and cationic hydrophilic guest molecules.
It is demonstrated that an optically transparent and electrically conductive polyethylene oxide (PEO) film is fabricated by the introduction of individualized single‐walled carbon nanotubes (SWNTs). The incorporated SWNTs in the PEO film sustain their intrinsic electronic and optical properties and, in addition, the intrinsic properties of the polymer matrix are retained. The individualized SWNTs with smaller diameter provide high transmittance as well as good electrical conductivity in PEO films.
A triblock copolymer, poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) was end-capped by acryloyl groups using a biodegradable oligolactide as spacer, and such biodegradable amphiphilic macromers could form micelles in water. A nanogel was prepared via polymerizing macromers in a micelle, and a macroscopic physical gelation was found upon heating a concentrated aqueous nanogel suspension. Such a sol–gel transition with a chemically crosslinked nanogel as the building block was thermoreversible. While the hydrogel affords a promising injectable biomaterial; this research reveals new physics of the thermogelling mechanism of amphiphilic block copolymers.
A novel method is described for transforming an anionic polymerization process into a cationic polymerization process assisted by organosilyl groups. The reaction of the p‐tolyldimethylsilyl end group of polystyrene and trifluoromethanesulfonic acid produced a silyl triflate end group that served as a macroinitiator for the living cationic polymerization of isobutyl vinyl ether. The Si O linkage in the block copolymers underwent specific cleavage by reaction with tetrabutylammonium fluoride.
A kinetic model of the amphiphilic star block copolymerization is developed. The star polymer species, resulting from star polymerization with dendrimer cores and hydrophobic monomers, are used as macroinitiators and initiate the graft polymerization of the hydrophilic monomers. Analytical expressions for the size distributions for the species formed in every step are derived. The method with monomers added to the reaction system in batches decreases the polydispersity index for the products obtained. It reaches a minimum if the monomer feed quantity is equal in every step. Therefore, the dimension and structure of the amphiphilic star block copolymers produced can be designed by using the proposed kinetic mechanism.
This paper develops a non‐spherical polymeric micelle using an amphiphilic block copolymer and a porphyrin crystalline structure. The nanoscale polymer micelles were characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM), revealing particle sizes of approximately 150 nm with a particular shape in the hexagonal lattice. The shape shows the selective uptake efficacy for the HeLa and macrophage cells, and inhibits phagocytosis against the macrophage.
The ability of star‐shaped, block copolymer‐based unimolecular micelles to encapsulate and transport guest molecules was studied. Analytical ultracentrifugation studies clearly showed that methyl‐orange guest molecules could be encapsulated and transported, together with unimolecular micelles consisting of 5‐arm, star‐shaped block copolymers with a poly(ethylene glycol) core and a poly(ε‐caprolactone) corona. Sedimentation‐velocity and equilibrium measurements were performed to determine the sedimentation coefficients, molar masses, and diffusion coefficients of the loaded, unimolecular micelles. It was observed that the transport of guest molecules by unimolecular micelles was a function of the molecular weight of the star‐shaped block copolymers and therefore also of their size.
We report a combined experimental and theoretical study of micellization of block copolymer with hydrophilic nonionic corona‐forming blocks and weak polyelectrolyte (wPE) core‐forming blocks with pH‐triggered solubility in aqueous solutions. We demonstrate that in addition to micelles with neutral cores, there exist two other types of micelles with PE‐ or ionomer‐like cores, in which monovalent counterions are released or condensed on core wPE block, respectively. The transition between the two types of micelles occurred upon changes in ionization of the PE core block and resulted in nonmonotonous changes of aggregation number as a function of pH. Such micelles with stimulus responsive cores represent promising nanocarriers for controlled delivery applications.
The dispersion of single‐walled carbon nanotubes (SWNTs) in a non‐polar solvent is controlled with a series of polystyrene‐block‐polybutadiene‐block‐polystyrene (PSBS) block copolymers that contain cholesteryl chloroformate (CC) in side‐chains. Esterification of CC with the partially hydroxylated polybutadiene (PB) blocks allows one to tune the polarity of the block copolymers, which decreases with the amount of CC attached. An excellent dispersion of weak polar SWNTs is observed with PSBS that contains a partially hydroxylated PB block. The dispersion is then significantly deteriorated when the amount of non‐polar CC moieties increases in the block copolymers. A good dispersion is achieved with a polymer that gives rise to strong SWNT–polymer interactions, which ensures contact of the polymer molecules with the nanotube surface, rather than a good solubility of the polymer dispersant in solvent. The stability of the SWNTs in solution arises from unique needle‐like nanowires of the block copolymer aligned perpendicular to the nanotube axis.
Reversible addition–fragmentation chain transfer (RAFT) chemistry can be effectively employed to construct macromolecular architectures of varying topologies. The present article explores the principle design routes to star, block, and comb polymers in the context of theoretical design criteria for the so‐called Z‐ and R‐group approaches. The specific advantages and disadvantages of each approach are underpinned by selected examples generated in the CAMD laboratories. In particular, we demonstrate how the modeling of full molecular weight distributions can be employed to guide the synthetic effort. We further explore the theory and practice of generating amphiphilic block copolymer structures and their self‐assembly. In addition, the article foreshadows how modern synthetic techniques that combine RAFT chemistry with highly orthogonal click chemistry can be employed as a powerful tool that furthers the enhancement of macromolecular design possibilities to generate block (star) copolymers of monomers with extremely disparate reactivities. Finally, the ability of RAFT chemistry to modify the surface of well‐defined nano‐ and microspheres as devices in biomedical application is detailed.
The free volume (voids) distribution in the lamellae of the conventional symmetric and amphiphilic diblock copolymers is studied via Monte–Carlo simulation based on the standard bond fluctuation model. Both in the conventional and amphiphilic block copolymers the voids are found to concentrate on the interfaces between the incompatible units, the magnitude of the effect being unexpectedly significant. A crystalline‐like ordering of voids with increase of the incompatibility between the different repeated units in amphiphilic copolymers is first reported and implications of this peculiarity for the morphology and mechanical properties of the amphiphilic copolymers are discussed.
In this work, we design and synthesize a kind of amphiphilic mushroom cap‐shaped particles with wettability difference on the opposite sides of the particles. Colloidal crystals consisting of uniformly oriented anisotropic particles were fabricated on the water–air interface based on the wettability difference of particles. This simple approach offers a new way for self‐assembly of anisotropic colloidal crystal by amphiphilic design of particles.
Polysilsesquioxane nanosheets with a thickness of four nanometers and lateral dimensions of several hundreds of nanometers were synthesized by polymerization of a trifunctional monomer in the layer space of montmorillonite as the confined environment.
AFM image of a polymethylsilsesquioxane nanosheet. 相似文献
It is known that Polyamide 6 absorbs water in its amorphous phase. The exact composition of the amorphous phase will determine the uptake process. The heterogeneity in the amorphous phase with respect to plasticization by water uptake is quantified in this paper using NMR relaxometry. It is shown that water occupies and plasticizes only a small part (∼6%) of the nylon matrix. This part is located in between the crystalline domains where polymer chain mobility is higher. At low moisture content (<4%) water molecules are tightly bound to the polymer and have the same dynamics. A highly mobile pool of guest‐hydrogen nuclei is detected starting at a moisture content of 4%. Here, water is absorbed in clusters and the interaction between the polymer chains and water molecules decreases, leading to decoupling of the dynamics of water and polymer.
