Stable aqueous dispersions of nanoparticles were prepared by polyelectrolyte complex formation between well‐defined poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propane sodium sulfonate) and poly(ethylene glycol)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] diblock copolymers. Controlled synthesis of the copolymers was achieved by water‐based atom transfer radical polymerization (ATRP). The nanoparticles were characterized by a quite narrow and monomodal size distribution as evidenced by dynamic light scattering (DLS) and confirmed by atomic force microscopy (AFM) after solution casting and freeze‐drying.
Disulfide‐functionalized hyperbranched poly(amido amine)s (HPAMAMs) were synthesized by Michael addition polymerization of N,N'‐cystaminebisacrylamide and 1‐(2‐aminoethyl)piperazine. The novel HPAMAMs displayed bright fluorescence, and the emissions bands cover nearly the whole visible wavelength range. When polymer solutions were excited at 330–385, 460–490, and 510–550 nm, blue, green, and red solutions were observed, respectively. The HPAMAMs are biodegradable and they can be easily cleaved by 2‐mercaptoethanol or glutathione, leading to a decrease in the fluorescence intensity. Studies of applications of the biocompatible and biodegradable HPAMAMs in fluorescence imaging technology and biological science are in progress.
Suitably activated, (Cp*){N(tBu)C(Me)N(Et)}ZrMe2 is known to initiate the ‘living’ and isotactic‐selective polymerization of alk‐1‐enes, and it can be used to synthesize block copolymers and stereoblock polymers. We report a full molecular kinetic investigation of propene, but‐1‐ene, and hex‐1‐ene polymerization with a MAO‐activated catalyst system. By combining NMR microstructural polymer analysis with QM modeling of the active species, the complicated regio‐ and stereochemistry of the polyinsertion process, as well as the active chain‐transfer pathways, are investigated. The perspectives and limitations of this catalyst for application in (stereo)block polymerizations are discussed.
Summary: The synthesis and thermal, redox and photoluminescence properties of a soluble donor‐acceptor polyplatinayne with the electron‐accepting silole ring and its model compound are described. The polymer has an optical band gap of 2.10 eV which is much lower than that of thienyl‐ or silyl‐bridged congeners. The incorporation of electron‐accepting silole unit in the metallopolymer main chain creates a new π‐conjugated system that features unique donor‐acceptor characteristics.
Blue emission of oxygen‐doped tertiary amine (triethylamine), a key unit of fluorescent poly(amido amine) dendrimer, was demonstrated. It was found that the fluorescence intensity could be further enhanced if the tertiary amines locate densely in the dendrimer interior as the branching sites. Moreover, a solvatochromic phenol blue, instead of oxygen, is able to induce the blue fluorescence of the tertiary amino‐branching sites based on a guaranteed host‐guest complexation of phenol blue molecules and dendrimer interior.
This paper reports a new polyimide design with high internal free volume elements for fast mass transport simultaneously with high selectivity. Here, we show that the polymer design using a three‐dimensional rigid molecular structure having internal void space can lead to the formation of high fractional free volume with proper cavity size to separate small gas molecules with high selectivities as high permeabilities. These findings could strongly impact emerging gas separation applications using polymeric membranes such as natural gas purification and biogas purification to get clean energy resources.
Starting in biochemistry and pharmaceutical chemistry, combinatorial methods, automated synthesis and high‐throughput characterization are being further developed for organic synthesis and polymer research. The development is strongly driven by the achievements in biochemistry and pharmaceutical chemistry and the need to minimize the time‐to‐market for novel polymeric products. The success of high‐throughput methodologies in polymer science is partially limited by the commercially available hardware (synthesizers, workstations, robots, online‐characterization instruments, etc.) and software. A short overview of commercially available equipment for polymer research is provided in this Review.
Summary: A methacrylate‐functionalized poly(ethylene glycol) macromonomer was copolymerized at the surface of methacrylate‐derivatized maghemite nanoparticles. After silylation of the magnetic core with methacryloxypropyltrimethoxysilane, two grafting procedures based on either a direct copolymerization reaction in water or an inverse emulsion polymerization were compared. A direct copolymerization led to low polymer surface amounts, whereas an inverse emulsion process allowed nanocomposite particles containing up to 90 wt.‐% polymer to be obtained.
TEM picture of maghemite‐PEG hybrid particles. 相似文献
Micrometer‐sized polydiacetylene (PDA) vesicle patterns on titanium substrates have been successfully fabricated by using a micromolding in capillaries (MIMIC) technique. The shape and width of the PDA patterns are well matched with polydimethylsiloxane (PDMS) molds used in the MIMIC process. However, the thicknesses of the patterned films are less than the depths of the PDMS molds, which may be a consequence of the poor water wettability of the PDMS and/or low concentrations of the PDA solutions. Heat‐treatment of the solid substrate, immobilized with blue‐phase PDAs, induces a blue‐to‐red‐phase transition and results in the formation of patterned fluorescence images.
A method to prepare shape‐changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main‐chain polyester and subsequently crosslinked into a nanometer‐sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature‐dependent transmission electron microscopy. The phase transition‐induced shape change leads to strongly shape anisotropic nanosized elastomer particles.
Olefin isomerization side reactions that occur during ADMET polymerizations were studied by preparing polyesters via ADMET and subsequently degrading these polyesters via transesterification with methanol. The resulting diesters, representing the repeating units of the previously prepared polyesters, were then analyzed by GC‐MS. This strategy allowed quantification of the amount of olefin isomerization that took place during ADMET polymerization with second generation ruthenium metathesis catalysts. In a second step, it was shown that the addition of benzoquinone to the polymerization mixture prevented the olefin isomerization. Therefore, second generation ruthenium metathesis catalysts may now be used for the preparation of well‐defined polymers via ADMET with very little isomerization, which was not possible before.
Summary: The nanostructuring of ORMOCER® to form inverse opals is described. For this purpose a polymer opal is used as a template and infiltrated with liquid ORMOCER®. After photopolymerization of the resin the host opal is dissolved in tetrahydrofuran and an ORMOCER® inverse opal is obtained. It shows excellent periodicity (by SEM) and optical properties to reveal a high degree of face centered cubic order. This replication process leads to a nanostructured photonic crystal with the outstanding mechanical properties of ORMOCER® and high temperature stability up to 350 °C.
ORMOCER® inverse opal annealed at 200 °C for 10 h. 相似文献
Summary: A simple method for the direct catalytic heterogeneous modification of polysaccharides is presented. The novel method is exemplified by the combination of organic acid‐catalyzed esterification and copper‐catalyzed Huisgen reaction (click chemistry) to attach a fluorescent probe to solid cellulose. The heterogeneous ‘organoclick’ derivatization of cellulose allows for a mild, highly modular surface modification of cellulose under environmentally benign reaction conditions.
Schematic of the combined organic acid‐catalyzed esterification and copper‐catalyzed Huisgen reaction (click chemistry) to modify a polysaccharide with a fluorescent probe. 相似文献
A PDA based sensor, derived from a di‐(2‐picolyl) amine (DPA) substituted diacetylene monomer, displayed a selective colorimetric change and a large fluorescence enhancement in the presence of lead ions. The lead selective PDA‐based chemosensor enabled easy detection of the presence of lead in 100% aqueous solution by the naked‐eye.
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.
Sixteen parallel polymerization reactions of 2‐ethyl‐2‐oxazoline have been performed at different temperatures in an automated synthesizer that allowed individual heating of each reactor. During the reactions samples were taken automatically, which were characterized by means of both online GPC and offline GC, in order to optimize the reaction temperature and to determine the activation energy of the polymerization.
In this study, we have synthesized highly photoluminescent TiO2/poly (phenylene vinylene) (PPV) hybrid nanoparticle‐polymer fibers by electrospinning a PPV precursor added to a TiO2 sol‐gel solution. The diameters of the hybrid fibers ranged from 100–300 nm and the average size of TiO2 nanoparticles within the fibers was 10–60 nm. FT‐IR analysis indicated that a new band around 1 632 cm−1 assigned to the Ti O C vibration appeared, which resulted in the stronger luminance of the fluorescence of the TiO2/PPV hybrid fibers compared to free standing PPV nanofibers.
Multi‐walled carbon nanotubes (MWNT) purified by acidic solution were processed with PMMA via an in‐situ polymerization. Experimental evidences indicate the role of radical initiator (AIBN) and MWNT, showing increases of polymerization rate and MWNT diameter. Induced radicals on the MWNT by AIBN were found to trigger the grafting of PMMA. Moreover, the solvent cast film showed a better nanoscopic dispersion of MWNT and possibilities of CNT composites in engineering applications.
Fractured surface of multi‐walled carbon nanotube composite with PMMA prepared by in‐situ bulk polymerization. 相似文献
A thiol‐modified siRNA targeting the enhanced green fluorescence protein (eGFP) gene was conjugated with RAFT‐synthesized, pyridyl disulfide‐functional poly(PEG methyl ether acrylate)s (p(PEGA)s). siRNA‐p(PEGA) conjugates demonstrated significantly enhanced in vitro serum stability and nuclease resistance compared to the unmodified and thiol‐modified siRNA. The complexes of siRNA‐p(PEGA) conjugates with a fusogenic peptide, KALA ((+)/(–) = 2) inhibited the protein expression approximately 28‐fold more than the KALA complex of the unmodified siRNA. The protein inhibition caused by siRNA‐p(PEGA)‐KALA complexes (56 ± 5%–58 ± 3% of the fluorescence expressed in non‐treated cells) was comparable to the effect of the unmodified siRNA‐lipofectamine complex (77 ± 7%).
