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 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.
Cystamine, when employed as a cross‐linking agent, leads to poly(amidoamine) networks, which on reaction with 2,2′‐dithiodipyridine turn into linear poly(amidoamine)s with side dithiopyridyl groups that easily undergo exchange reactions with reduced L ‐glutathione, a model thiol‐containing biologically active peptide. The resultant products represent the first examples of soluble poly(amidoamine)–peptide conjugates in which the peptide moieties are linked to the polymer chain by S S bonds stable in blood, but cleavable inside cells.
A polymer–surfactant micellar complex has been studied as a fluorescence resonance energy transfer (FRET) donor to fluorescein‐labeled DNA (ssDNA‐Fl). In water, the molar absorptivity and fluorescence quantum efficiency of cationic poly(fluorene‐co‐phenylene) (c‐PFP) are substantially increased in the presence of non‐ionic surfactants. A TEM microscopic study shows the formation of a nanowire micellar complex of c‐PFP and the surfactants. About a 400% enhancement of the FRET signal is measured in c‐PFP/ssDNA‐Fl with Brij 30, relative to that without surfactants. The signal amplification is successfully modulated using different types of non‐ionic surfactants which perturb the complexation, fine‐structure of the complex (i.e., donor‐acceptor separation), and the resulting energy transfer process.
An amplified fluorescence turn‐on assay for mercury(II) detection and quantification was developed. This method makes use of specific thymine/mercury(II)/thymine coordination to capture Fl‐labeled DNA onto NP surface. Addition of a cationic conjugated polymer leads to an amplified Fl signal in solution. A sigmoidal Hg2+ working curve is obtained at fixed [NP] with a detection limit of 0.1 × 10−6 M . However, by reducing [Hg2+] and [NP] simultaneously, while maintaining [Hg2+]:[DNA duplex] = 3:1, a linear calibration curve is observed with a detection limit of 5 × 10−9 M . The CCP‐assisted mercury(II) assay shows potential applications in environmental mercury detection and for industrial process control.
A new platform has been developed for DNA lesion detection using a cationic conjugated polymer (CCP). DNA that contains two adjacent thymine bases is irradiated with ultraviolet light to allow for the formation of cyclobutane pyrimidine dimers and pyrimidine–pyrimidone dimers. The DNA lesions block the primer extension, and the base labeled with fluorescein cannot be incorporated into the DNA strand. Addition of the CCP leads to inefficient fluorescence resonance energy transfer (FRET) from CCP to fluorescein. For the case without DNA lesions, successful primer extension allows for efficient FRET between them. In view of the FRET signal changes, the DNA lesions can be detected. This new protocol offers a convenient detection for DNA lesions in aqueous solution without any isolation and washing steps.
Reactions between the ethylene groups in the backbone of conjugated polymers under UV illumination and heat treatment result in the cross‐linking of the main polymer chains. The cross‐linking leads to two simultaneous results in the polymer: excellent solvent resistance and increased bandgap. Using this reaction, three‐color polymer light‐emitting diodes (PLEDs) with a multi‐layer structure can be easily realized by a dry photo‐pattern in an active‐gas‐free environment. Multi‐layer blue devices with dramatically enhanced efficiency can also be achieved conveniently.
The synthesis and physico‐chemical characterisation of biodegradable multiblock polymer drug carriers based on poly(ethylene glycol) (PEG) are described. The blocks of PEG ( = 2 000) are interconnected by an enzymatically degradable tripeptide derivative consisting of one Lys and two Glu residues. An anticancer drug, doxorubicin (Dox), was attached to the polymer carrier by a Gly‐Phe‐Leu‐Gly tetrapeptide spacer, which is also susceptible to degradation by lysosomal enzymes. A targeting polyclonal antibody was covalently linked to the polymer‐Dox conjugate by the aminolytic reaction of reactive sulfosuccinimidyl ester groups of the polymer with the protein. The resulting antibody‐polymer‐drug conjugates were characterised by SEC, UV/VIS spectrophotometry and amino acid analysis. Although the studied polymers show only a moderate antiproliferative activity against concanavalin A‐stimulated murine splenocytes and a murine T‐cell EL 4 lymphoma in vitro, they exhibited significant antitumour efficiency against murine T‐cell EL 4 lymphoma in vivo.
Smectic‐A elastomers combine one‐dimensional translational order of rod‐like segments with the rubber elasticity of a polymer network. In recent years, detailed investigations were carried out on elastomers showing a global prolate chain conformation. In this communication, the first experiments on fluorinated SA elastomers exhibiting a global oblate chain conformation are presented, where the polymer chains are on average compressed along the layer normal of the lamellar phase structure. The mechanical anisotropy is studied by means of thermoelastic experiments and stress–strain measurements. For the first time, the layer compression modulus B of smectic elastomers is directly measured. B is significantly larger as compared to conventional low molar mass liquid crystals and decreases significantly with increasing local disorder introduced by the isotropic crosslinker.
A cationic water‐soluble polyfluorene (P2) containing a high density of tetraalkylammonium side chains in polymer backbone was synthesized and characterized. The polymer shows excellent water solubility up to 100 mg · mL−1 as well as high photoluminescence (PL) quantum yield of 44% in water. The relatively high cationic density and appropriate side chain length of the polymer are the key factors to achieve such high water solubility. The reduction potential of P2 is decreased as compared with its neutral polymer, reflecting the enhanced electron injection abilities. The standard NPB/Alq3 device using such a polymer as the electron injection layer shows nearly three‐fold enhancement in the electroluminescence (EL) efficiency.
Amphiphilic polymer brushes grafted onto gold nanoparticles impart distinct solvent‐responsive behavior via the change to particle size and surface chemistry and, therefore, wide application prospects can be expected. Coarse‐grained simulations are performed for block and/or mixed polystyrene (PS)/poly(ethylene oxide) (PEO)‐modified amphiphilic gold nanoparticles (AuNP) to investigate their responsive behavior in five different solvents by analyzing their morphology, distribution density profiles, and gyration radii. Typical core–shell, Janus‐type, buckle‐like, ring‐like, jellyfish‐like, and octopus‐like morphologies are formed. Influence of block sequence, mixing mode, and several other effects are discussed. Responsive particle size and surface hydrophilicity can be successfully reproduced by altering solvents.
Polycondensation of 1‐(2‐pyrimidinyl)pyrrole with 2,7‐dibromo‐9,9‐dioctylfluorene via Ru‐catalyzed direct arylation gives the corresponding conjugated polymer with a molecular weight of 19 800 in 86% yield. The introduction of directing group, 2‐pyrimidinyl substituent, into the pyrrole monomer induces ortho‐metalation and provides the site‐selective direct arylation polycondensation at the α‐position of pyrrole unit without the protection of β‐position. The removal of 2‐pyrimidinyl substituent on the pyrrole unit proceeds efficiently and results in the enhancement of coplanarity along the main chain of the polymer.
Hierarchical poly(3‐hexylthiophene)(P3HT)/carbon nanotube (CNT) supramolecular structures were fabricated through a bottom‐up CNT induced P3HT crystallization strategy. P3HT nanowires growing perpendicular from CNT surface have uniform width and height. The density and the length of these nanowires can be controlled by tuning the P3HT/CNT mass ratio. The quasi‐isothermal crystallization process monitored by in situ UV–Vis spectroscopy indicates that CNTs can greatly enhance the P3HT crystallization, and the P3HT nanowire formation follows first‐order kinetics. Such bottom‐up strategy provides a general approach to build 2D functional conductive supramolecular structures that will lead to numerous applications in nanoscale electronics.
But‐3‐en‐1‐ol has been pre‐protected by triisobutylaluminium and terpolymerized with ethylene and norbornene by rac‐[Et(Ind)2]ZrCl2/MAO catalysts. The strong polarity of diisobutyl(but‐3‐en‐1‐oxy)aluminum causes a slight reduction in the catalyst activity and yields a small fraction of crystallinity. The but‐3‐en‐1‐ol content in the terpolymer is as high as 3.2% and can be readily adjusted by varying the reaction conditions. When the norbornene/ethylene ratio is over 10, the norbornene incorporation efficiency is not affected by the polar monomer and is close to that of the copolymerization. Similar to the ethylene/norbornene copolymers, the thermal properties of the obtained terpolymers are mainly determined by their norbornene contents.
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: New polymer gelators consisting of poly(propylene glycol) or poly(ethylene glycol) and L ‐lysine‐based low‐molecular‐weight gelators have been developed. These polymer gelators were synthesized according to a simple procedure with high reaction yield, and formed organogels in many organic solvents. The organogelation mechanism was proposed from the transmission electron microscopy and FTIR spectroscopy studies.
Structures of the polymer gelators synthesized here. 相似文献
Summary: A highly selective protein assay was created which combines the fluorescent ratiometric technique based on FRET with the light‐harvesting properties of conjugated polymers. The cationic poly[(9,9‐bis(6′‐N,N,N‐trimethylammonium)‐hexyl)‐fluorene phenylene] bromide (PFP‐NMe) and the negatively charged biotinylated fluorescein probe (Fl‐B) were used to detect the target protein streptavidin optically. The strong electrostatic interactions between PFP‐NMe and fluorescein result in efficient FRET from PFP‐NMe to fluorescein. In the presence of streptavidin, however, the biotin moiety of Fl‐B specifically associates with streptavidin and the fluorescein molecule is buried deeply in the adjacent vacant binding sites. This separates the fluorescein spatially from the PFP‐NMe moiety, resulting in inefficient FRET from PFP‐NMe to fluorescein. Although a nonspecific protein, such as BSA, shows nonspecific interactions with PFP‐NMe, it does not affect the fluorescent ratio value of PFP‐NMe to fluorescein. Hence, the charged neutral complex of two oppositely charged conjugated polymers can eliminate the nonspecific interactions, and thus optimize their application in protein assays.
A schematic representation of the protein assay operation. 相似文献
Summary: A multistep synthetic procedure for preparing novel C60‐anchored two‐armed poly(tert‐butyl acrylate) was developed. First, two‐armed poly(tert‐butyl acrylate) bearing a malonate ester core with well‐controlled molecular weight was synthesized through atom transfer radical polymerization. The effective Bingel reaction between C60 and the well‐defined polymer was then carried out to yield C60‐anchored polymer. GPC, 1H NMR, and UV‐vis spectroscopy indicated that the C60‐anchored polymer was a monosubstituted and ‘closed’ 6,6‐ring‐bridged methanofullerene derivative.
Schematic of a novel C60‐anchored two‐armed polymer. 相似文献
Summary: An in‐situ mineralization process in the presence of thermo‐responsive microgels leads to the formation of well‐defined hybrid materials. Experimental data suggest that control of the mineralization process in the presence of the microgels offers the possibility to obtain sub‐micrometer‐sized hybrid particles or macroscopic hybrid hydrogels. The rapid formation of CaCO3 crystals in the microgel structure favors the preparation of the hybrid particles wherein inorganic crystals cover the shell layer of the microgel. The slow formation of CaCO3 crystals leads to the simultaneous self‐assembly of the microgel particles on the bottom of the reaction vessel, and the formation of a physical network. It has been demonstrated that hybrid hydrogel materials with different calcium carbonate contents and temperature‐dependent swelling‐deswelling properties can be prepared.
Formation of a hybrid hydrogel by the vapor diffusion method. 相似文献
Here, we show that a poly(ethylene oxide) polymer can be physically cross‐linked with silicate nanoparticles (Laponite) to yield highly extensible, bio‐nanocomposite fibers that, upon pulling, stretch to extreme lengths and crystallize polymer chains. We find that both, nanometer structures and mechanical properties of the fibers respond to mechanical deformation by exhibiting strain‐induced crystallization and high elongation. We explore the structural characteristics using X‐ray scattering and the mechanical properties of the dried fibers made from hydrogels in order to determine feasibility for eventual biomedical use and to map out directions for further materials development.
