A sterically encumbered m‐terphenyl oxacyclophane substituted with two aryl iodide substituents has been prepared as a versatile monomer for the preparation of π‐conjugated polymers. The monomer has been used to prepare a poly(p‐phenylene ethynylene) derivative (P1) incorporating oxacyclophane units as canopies that shield one side of the π‐system from inter‐chain interactions. The photophysical properties of P1 in dilute solution compare well to those of a poly(p‐phenylene ethynylene) derivative (P2) that lacks the canopy. The presence of the steric canopy leads to a diminished inter‐chain interaction in the solid state and enhances the kinetic response of P1 to vapors of nitro‐organics such as TNT, presumably by increasing the permeability of P1 to these analytes over that of P2.
A polymeric film of a biodegradable poly(p‐dioxanone) was grown from 490 nm silica particles by monolayer formation via self‐assembly of hydroxy‐terminated triethoxysilane and subsequent surface‐initiated ring‐opening polymerization of p‐dioxanone. The resulting silica/poly(p‐dioxanone) hybrid particles were characterized by means of 1H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, field‐emission scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy.
It is the general consensus that in Gilch polymerizations the 1,4‐bis(chloromethylene)benzene starting material first changes into p‐quinodimethane intermediates which then act as the real monomers. However, direct observation of these intermediates has not been possible so far. This is because usually the p‐quinodimethane auto‐initiates its rapid radical polymerization instantaneously, keeping its concentration extremely low throughout the whole process. Here it is shown that, when the reaction is carried out at very low temperatures, the formation of p‐quinodimethane still proceeds but chain growth is suppressed. Hence, the concentration of the active monomer reaches a level sufficient for NMR analysis.
Oxygen is shown to act as an efficient molar‐mass regulating agent in Gilch syntheses of PPV. As a scavenger, it undergoes instantaneous recombination with the initiating diradicals as soon as they appear in the system. Regular polymer formation can only start when all oxygen has been used, proceeding predominantly as chain‐growth polymerization of the p‐quinodimethane monomers. Since all radical species involved in this Gilch process are diradicals, some polyrecombination events occur in parallel. Therefore the initially formed peroxy diradicals are also incorporated into the resulting chains. Later, they break under very mild conditions, thereby causing a systematic decrease of the final molar mass of PPV.
Three‐dimensionally ordered macroporous (3DOM) syndiotactic polystyrene (sPS) and poly(p‐methyl styrene) (sPPMS) are synthesized using silica colloidal crystal templates with varied diameters in the range of 548–214 nm, and the effect of polymerization space on the conformation of the resulting 3DOM polymers is investigated by spectroscopy and thermal analysis. In‐situ polymerizations of styrene and p‐methyl styrene within the silica templates induce the resulting 3DOM polymers with different conformations and packing of chains, which are different from those of bulk polymers prepared in the absence of templates. Polymerizations in restricted silica templates result in un‐helixication of 3DOM sPS chains and helixication of 3DOM sPPMS chains.
Summary: A new water‐soluble cationic ammonium‐functionalized poly(p‐phenylenevinylene) (PPV‐NEtMe) was successfully synthesized and exhibited high sensitivity (Ksv = 6.9 × 107 M −1) on rubredoxin, a type of anionic iron‐sulfur (Fe‐S) proteins. Further investigation showed that the biosensitivity of the cationic conjugated polymer is strongly dependent on the nature of the buffer solution and the concentration of the conjugated polymer used in the analyses.
The schematic diagram of anionic rubredoxin detected by PPV‐NEtMe. 相似文献
Poly(L ‐lactic acid)‐block‐poly(poly(ethylene glycol) monomethacrylate) (PLLA‐b‐PPEGMA) has been prepared by the ring‐opening polymerization of lactide with a double‐headed initiator, 2‐hydroxyethyl 2′‐methyl‐2′‐bromopropionate (HMBP), followed by atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethacrylate (PEGMA). PLLA‐b‐PPEGMA nanoparticles with encapsulated Fe3O4 are prepared by a solvent evaporation/extraction technique, and then further functionalized with folic acid, a cancer targeting ligand. Our results show that such functionalized PLLA‐b‐PPEGMA nanoparticles have good potential as carriers for targeted drug delivery in cancer treatment.
The complexation of bile acids with various solvated polycations was studied. A one‐to‐one complex was precipitated when an aqueous solution of cholic acid sodium salt (CA) was mixed with aqueous solutions of 3,3‐ionene and grew to form crystals with needle‐like morphology, 3 millimeters in length. Hydrogen bonding of hydroxyls at the steroid face and the spacing between cationic sites of polycations were crucial for the formation of the giant needle.
Crossed polarizing microscopic photograph of the complex composed of cholic acid sodium salt and 3,3‐ionene. 相似文献
Poly(3‐hexylthiophene)‐b‐poly(γ‐benzyl‐L ‐glutamate) (P3HT‐b‐PBLG) rod–rod diblock copolymer was synthesized by a ring‐opening polymerization of γ‐benzyl‐L ‐glutamate‐N‐carboxyanhydride using a benzylamine‐terminated regioregular P3HT macroinitiator. The opto‐electronic properties of the diblock copolymer have been investigated. The P3HT precursor and the P3HT‐b‐PBLG have similar UV–Vis spectra both in solution and solid state, indicating that the presence of PBLG block does not decrease the effective conjugation length of the semiconducting polythiophene segment. The copolymer displays solvatochromic behavior in THF/water mixtures. The morphology of the diblock copolymer depends upon the solvent used for film casting and annealing results in morphological changes for both films deposited from chloroform and trichlorobenzene.
PVA/SWNT dispersions yield aloe plant‐like crystals, where the leaves are single crystals templated by PVA coated SWNT. Longer growth times (≈18 months) lead to hexagonal rod‐like crystals. HR‐TEM images show evidence that PVA molecules are aligned parallel to the SWNT axis. WAXD, electron diffraction, and HR‐TEM observations of these aloe plant and hexagonal crystals suggests evidence for possible PVA‐SWNT epitaxy. Wide‐angle and electron diffraction data of these crystals also show that the structure seems to mimic the 2D hexagonal crystal packing of SWNT. PVA lattice images and moiré fringes were also observed in the leaf‐like crystals.
The mechanism of the Gilch polymerization leading to poly(p‐phenylene vinylenes) is still a matter of controversial discussion. Similar to some other research groups, we strongly favor a basically radical process. Moreover, we believe it is initiated by spontaneously formed diradicals. Here, we describe further experimental evidence which clearly supports the assumed initiation step: it is shown how the polymerization process is affected quantitatively when different amounts of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) are added as a scavenger. In full agreement with our expectations, the chain growth is either retarded or completely prevented, depending on the respective molar ratio of monomer and scavenger.
Summary: The vapor‐based synthesis and characterization of a reactive polymer, poly[(4‐formyl‐p‐xylylene)‐co‐(p‐xylylene)] ( 1 ), have been reported. The reactive polymer coating enables the immobilization of oligosaccharides via the chemoselective aldehyde‐hydrazide coupling reaction.
Phosphorescent conjugated polymers consisting of alternating p‐phenylene‐ethynylene and ‘para‐’ or ‘meta‐type’ Pt(II)‐salphen luminophore units have been synthesized. Side‐arms bearing different substituents (n‐alkoxy and acetylated‐sugar) have afforded contrasting emission properties that are attributed to the polymer conformation, extent of π‐stacking interactions and differences in chemical structure. Intriguing selectivity in luminescent sensing of metal ions has been observed.
A new soluble conjugated copolymer based on 2,7‐dibenzosilole and 4,7‐dithien‐2‐yl‐2,1,3‐benzothiadiazole units has been synthesized (PBSDTBT). Bulk heterojunction solar cell devices are fabricated using this material as the donor and [6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) as the acceptor. The power conversion efficiency is 1.6% under AM1.5 illumination. This material also shows a good VOC (0.97 V). The results are quite promising considering the relatively large bandgap (1.9 eV) of this polymer.
A simple method to fabricate polymer nanocomposites with single‐walled carbon nanotubes is reported, in which the nanotubes were reacted with poly(L ‐lysine) by using high‐speed vibration milling. The nanocomposites obtained were characterized by Fourier transform infrared (FT‐IR), UV–Vis spectroscopy, and thermogravimetric methods. The morphology as well as the dispersion of the carbon nanotubes were determined by scanning and transmission electron microscopy.
Summary: Poly(propylene oxide)‐amidoacids were used to intercalate montmorillonite clay to afford organoclays with an X‐ray basal spacing as wide as 81 Å. Differing from the ionic exchange between quaternary ammonium salts and the metal ions in clays, the intercalation mechanism involves a beta‐amidoacid chelation with sodium ions in the silicate interlayer confinement. With the end groups tethered on the silicate surface, the hydrophobic poly(propylene oxide)‐backbones self‐aggregate and consequently widen the interlayer space between neighboring silicate plates.
Postulated structure of the chelation of sodium ions by the poly(propylene oxide)‐amido acid. 相似文献
Atomic force microscopy characterization has been conducted to reveal the morphological difference between single‐ring bands in poly(butylene adipate) (PBA). Furthermore, morphological features of the ring‐less Maltese‐cross spherulites are compared to the ring‐band spherulites. Periodic changes in height seem to be common for either the ring‐band or ring‐less (Maltese‐cross) crystal domains; however, the steepness in height change is greater for the ring‐band crystal, while height change in the ring‐less crystal exhibits a terrace‐like layer pattern. In the ring‐band crystal region, the lamellar stalks, which taper off to pointed needle‐like stalks, monotonously protrude out of the layers of softer materials, with no signs of twisting, bending, or turning. In contrast, all lamellae in the ring‐less (Maltese‐cross) crystal region are uniform platelets arranged like flower petals in a layered pattern.
A consistent picture is presented of the mechanistic details and intermediates of the Gilch polymerization leading to poly(p‐phenylene vinylenes) (PPVs). In‐situ generated p‐quinodimethanes are shown to be the real monomers, and spontaneous formation of the initiating radicals is effected by dimerization of some of these monomers to dimer diradicals, the latter also being the reason why significant amounts of [2.2]paracyclophanes are formed as side‐products. Chain propagation predominantly proceeds by radical chain growth, occasionally interrupted by polyrecombination events between the growing α,ω‐macro‐diradicals. Based on this knowledge, oxygen is identified as a very efficient molar‐mass regulating agent, and the temporary gelation of the reaction mixtures is interpreted to be the consequence of a very high entanglement of the polymers immediately after their formation. Last but not least, it is rationalized why the usually considered constitutional defects in Gilch PPVs might not be the only and most relevant ones with respect to the efficiency and durability of the organic light emitting devices produced thereof, and why cis‐configurated halide‐bearing vinylene moieties should be perceived as being among the most critical candidates. These considerations result in the recommendation of straightforward measures that should lead to clearly improved PPVs.
Gelation of the reaction mixture and insolubility of the poly(p‐phenylene vinylenes) (PPVs) when isolated at this stage, but complete redissolution of the gel and excellent solubility of the resulting PPVs after further stirring for hours or days, is a phenomenon in Gilch polymerizations that has not been explained so far. It is verified that, in agreement with the literature, specific additives prevent gelation. However, it is also shown that chemical crosslinking is certainly not the reason for gel formation. Instead, it seems to be the consequence of a very high entanglement density in the pristine PPVs, which requires time for relaxation. The mentioned additives seem to support this dis‐entanglement process.
A novel approach to load a hydrophilic bovine serum albumin into drug carriers was proposed in terms of temperature‐programmed “shell‐in‐shell” structures, which were fabricated with poly(N‐isopropylacrylamide), poly(lactide), poly(ethylene glycol), and Au nanoparticles. Spherically well‐defined “shell‐in‐shell” structures were constructed by a modified‐double‐emulsion method (MDEM). The lower critical solubility temperature of the structures was manipulated to 36.4 °C which was confirmed by UV/Vis spectroscopy and DSC (Differential Scanning Calorimetry).
TEM image of the Au@PLLA‐PEG@PNIPAAm‐PDLA structure. 相似文献
