Spherical single‐chain‐particles of poly(N‐isopropylacrylamide) were prepared in aqueous solution above the lower critical solution temperature upon the addition of sodium dodecyl sulfate. The size of the single‐chain‐particles was investigated by means of transmission electron microscopy and viscosity measurements of the corresponding solutions, indicating the absence of inter‐chain entanglements among the single‐chain‐particles.
Schematic of the preparation of PNIPAM single‐chain‐globules in solution. 相似文献
A series of thermo‐responsive PNIPAM copolymers containing different amounts of fulgimide moieties has been synthesized via a polymer analogous reaction of poly(pentafluorophenyl acrylate). All copolymers were designed to exhibit a lower critical solution temperature (LCST) in water, which was only weakly dependent on the amount of incorporated chromophoric fulgimide groups. The copolymers showed a photocyclization of the fulgimide side groups upon irradiation with UV‐light accompanied with a color change. The closed form of the chromophore had a halftime of 136 min for the visible reisomerization and did not affect the LCST of the polymer. This led to the realization of a logic “NOT A” for the fulgimide containing PNIPAM, while a corresponding azobenzene containing PNIPAM resulted in a different logic “A implies B”.
We report the use of a PTFE‐based microfluidic device for the encapsulation of living, therapeutically‐active cells within monodisperse alginate microspheres. We present a novel microfluidic platform and a flexible experimental method for the production of alginate microspheres. Cell lines HEK293, U‐2 OS and PC12 were separately encapsulated using this method, with minimal loss of cell viability.
Several alkyl side chains are bonded to each polymeric repeat unit using both coordinated ligands and electrostatically bound counterions to directly control the interface curvature of the self‐organized structures. 2,6‐Bis(octylaminomethyl)pyridine is Zn‐coordinated to poly(4‐vinylpyridine) (P4VP) with dodecylbenzenesulfonate (DBS) counterions, leading to multicomb polymeric supramolecules, poly[(4VP)Zn(2,6‐bis(octylaminomethyl)pyridine)(DBS)2]. Coordination is evidenced by infrared spectroscopy and visualized by quantum chemical calculations. The amorphous hexagonal self‐organized structures are characterized using X‐ray measurements.
We report a new type of step‐growth radical addition‐coupling polymerization (RACP) involving consecutive addition of carbon‐centered radical derived from α,α′‐dibromo dibasic ester to NO double bond of C‐nitroso compound followed by cross‐coupling of carbon‐centered radical and in situ formed nitroxyl radical, which produces alternating copolymers with high molecular weight and unimodal molecular weight distribution from saturated and unsaturated monomers.
Summary: Silvered polyimide films have been fabricated by direct ion exchange of a damp‐dry poly(amic acid) film with an aqueous silver solution such as silver nitrate. Thermal curing of the silver(I )‐containing films under tension leads to cycloimidization of the poly(amic acid) into polyimide with a concomitant silver(I ) reduction and aggregation at both film sides to give reflective and conductive double‐surface‐silvered polyimide films. The metallized films retain the essential properties of the parent polyimide.
Surface morphology of the prepared double‐surface‐silvered polyimide films. 相似文献
Using molecular dynamics simulations with an OPLS force field, the lower critical solution temperature (LCST) of single‐ and multiple‐chain PNIPAM solutions in water is investigated. The sample containing ten polymer chains shows a sudden drop in size and volume at 305 K. Such an effect is absent in the single‐chain system. Large fluctuations of the physical properties of a short single‐chain prevent any clear detection of the LCST for the chosen model system, at least on the time scale of 200 ns. The results provide evidence that a critical number of PNIPAM monomer units must be present in the simulated system before MD simulations are capable to detect conformational changes unambiguously.
PS‐b‐PAA spherical micelles with a liquid core and a PAA shell are prepared with the assistance of 1,2‐dichloroethane. During the process of adding a mixture of PNIPAM‐b‐P4VP and PEG‐b‐P4VP, multi‐layered micelles with a mixed corona that consists of both PNIPAM and PEG chains are constructed through the electrostatic interaction and hydrogen bonding between the PAA block and the P4VP block. When heating above the LCST, the PNIPAM chains collapse onto the PAA/P4VP complex layer while the PEG chains still stretch into the solution through the collapsed PNIPAM layer, which leads to the formation of hydrophilic channels around the PEG chains. The ibuprofen encapsulated in the hollow space can diffuse through the channels and its release rate can be controlled by changing the ratio of PEG chains to PNIPAM chains in the corona.
The fabrication of a thermoresponsive biohybrid double hydrophilic block copolymer (DHBC) by a cofactor reconstitution approach is reported. Poly(N‐isopropylacrylamide) (PNIPAM) bearing a porphyrin moiety at the chain terminal, PPIXZn‐PNIPAM, is synthesized by the combination of ATRP and a click reaction. The subsequent cofactor reconstitution process between apomyoglobin and PPIXZn‐PNIPAM affords well‐defined myoglobin‐b‐PNIPAM protein–polymer bioconjugates. Behaving as typical responsive DHBCs, the obtained myoglobin‐b‐PNIPAM biohybrid diblock copolymer exhibits thermo‐induced aggregation behavior in aqueous solution as a result of the presence of the thermoresponsive PNIPAM block, as revealed by temperature‐dependent transmittance, dynamic laser light scattering measurements, transmission electron microscopy, and scanning electron microscopy. This work represents the first report of the preparation of responsive biohybrid DHBCs by the cofactor reconstitution process.
The preparation of a bisphenol‐A carbonate copolymer, containing Cu‐diimine units with nonlinear optical (NLO) properties, and its MALDI‐TOF mass spectrometric characterization are reported. Contrary to the usual synthetic method, NLO groups were inserted directly into a commercial polycarbonate by prolonged heating at 250 °C. This innovative procedure allows to obtain a Cu/diimine‐containing polymer of high molecular weight.
Rapidly shrinking poly(N‐isopropyl acrylamide) (PNIPAM) hydrogels are prepared by crosslinking with self‐assembled nanogels that consist of cholesteryl‐ and methacryloyl‐substituted pullulan (CHPMA). The CHPMA nanogel (Rh = 26.4 nm) was used as a crosslinker for a hydrophilic nanodomain. Transmission electron microscopy images of the nanogel‐crosslinked PNIPAM hydrogel reveal a well‐defined nanoporous structure. The nanogel‐crosslinked PNIPAM hydrogel shows rapid shrinking based on its structure. The shrinking half‐time was ≈2 min, which is about 3 400 times faster than that of a PNIPAM hydrogel crosslinked by methylene(bisacrylamide).
A series of novel temperature and pH responsive block copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(L ‐lysine) (PLL) were synthesized. The effect of pH and the length of PLL on the lower critical solution temperature (LCST) of PNIPAM, and the self‐assembly of these PLL‐based copolymers induced by temperature and pH changes were investigated by the cloud point method, dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM). These PNIPAM‐b‐PLL copolymers can self‐assemble into micelle‐like aggregates with PNIPAM as the hydrophobic block at acidic pH and high temperatures; and at alkaline pH and low temperatures, they can self‐assemble into particles with PLL as the hydrophobic block. The copolymers may have potential applications in biotechnological and biomedical areas as drug release carriers.
Conformational analysis of macromolecular structures reveals interesting higher‐order spatial arrangements. Analyzing these features as a function of time provides insights into the dynamical behavior of these systems and the identification of relevant subdomains. We present some visual‐analytic methods that we devised to explore the spatial‐temporal properties from molecular dynamics simulation data. These methods automatically detect common features and connect them to properties of interest. These methods yield physical insights that are not easily obtainable with existing methods for particle simulation data, as illustrated for polyacetylene interacting with a carbon nanotube.
Conductive Polyamide 6 (PA‐6) nanofibers were prepared by making a conductive polypyrrole coating obtained by a polymerization of pyrrole molecules directly on the fiber surface. A solution of PA‐6 added with ferric chloride in formic acid has been electrospun and the fibers obtained showed an average diameter of 260 nm with a smooth surface. The fibers have been then exposed to pyrrole vapours and a compact coating of polypyrrole was formed on the fiber surface. The growth of the coating was monitored by measuring the increment of the fiber diameter and by FT‐IR spectroscopy. The same technique was used to study the interaction between the ferric chloride and the polyamide chains. The polypyrrole coating on the fibers turned out to be conductive with a pure resistive characteristic and the stability of the conductivity was evaluated in air at room temperature.
An efficient procedure to create oriented polymer films with strongly anisotropic properties is described. It is based on a two‐step process combining a photochemical and a thermal aligning step. The orientation of the polymer parallel or perpendicular to linearly polarised incident light can be adjusted. The method presented allows for simple fabrication of films with anisotropic absorption and emission characteristics with a dichroism of 0.7 and a fluorescence anisotropy of about 8.
In the present paper, the microwave (MW)‐assisted synthesis of hydrogel forming polymers based on poly(acrylic acid) ( 1 ) is described. The polymer analogous condensation reaction between adamantyl moieties bearing free amino groups and poly(acrylic acid) ( 1 ) was carried out simply by mixing both components and subsequent use of MW protocol. The mixture was irradiated for 20 min without the addition of solvents or coupling agents. Aqueous solutions of the sodium salts of the obtained hydrophobically modified poly(acrylic acid)s showed a very high viscosity due to the intermolecular association of the hydrophobic side chains and the resulting formation of physical networks. By the addition of randomly methylated β‐cyclodextrin (RAMEB), the rheology of these systems could be influenced significantly.
A two‐armed polymer with a crown ether core self‐assembles to produce macroporous films with pores perpendicularly reaching through the film down to the substrate. A possible assembling mechanism is discussed. The pore size can be conveniently adjusted by changing the solution concentration. These through‐hole macroporous films provide a template for fabricating an array of Cu nanoparticle aggregates.
The preparation of self‐assembled polyaniline (PANi) microspheres via facile interfacial oxidation polymerization of aniline in the presence of DL ‐tartaric acid dopant is reported. Compared with PANis reported in the literature, the PANi prepared in this study exhibits a nanorod‐bundle morphology with exceptionally high crystallinity. These nanorods or nanorod bundles can self‐assemble into microspheres with unique alignment. The chemistry, morphology, and crystal structure of DL ‐tartaric acid doped microspheres were studied using SEM, TEM, SAED, XRD, and FTIR.
Magnetic nanomaterials have been studied in order to generate novel nanocomposites that display both the magnetic properties of the nanoparticles and the ability to self‐assemble of the amorphous block copolymer matrix. Towards this goal, iron oxide magnetic nanoparticles have been modified with PS brushes by ATRP in order to improve both the dispersion and the affinity of the nanoparticles with one of the blocks of a polystyrene‐block‐polybutadiene‐block‐polystyrene block copolymer. This method of preparation of nanocomposites opens new strategies for the generation of magnetic nanomaterials. The samples are characterized using DSC and atomic and magnetic force microscopies.
