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 novel chlorotitanium calix[4]arene complex was synthesized and tested, without activator, as catalyst for the polymerization of L ‐ and rac‐lactide under solvent‐free conditions. The catalyst displayed high activity, which depended on the monomer‐to‐catalyst molar ratio, and led to highly isotactic PLLA. Despite concomitant transesterification during the polymerization, polylactide formation was well‐controlled, the molar mass distribution indexes remaining in the restricted range of 1.2–1.4.
The oxidant, Fe(III) tosylate, was used in the vapour phase polymerisation (VPP) of PEDOT. The amphiphilic co‐polymer poly(ethylene glycol‐ran‐propylene glycol) was added and its influence examined. Both the PEDOT conductivity and optical contrast range increased with the inclusion of the co‐polymer, with the maximum being recorded at 4 wt.‐%. Loadings higher than this resulted in a systematic decrease in both conductivity and optical contrast. Evidence indicates that in addition to the beneficial anti‐crystallisation effect to the oxidant layer, the co‐polymer also reduces the effective reactivity of the oxidant, as demonstrated by slower polymerisation rates. Confirmation of the change in polymerisation rate was obtained using a quartz crystal microbalance (QCM). The slower polymerisation rate results in higher conductivity and optical contrast; however, XPS data confirmed that the co‐polymer remained within the PEDOT film post‐washing and this result explains why the performance decreases at high surfactant loadings.
The catalytic behavior of three bis(phenoxy‐imine) group‐4 transition‐metal complexes (M = Ti, Zr, Hf), with iBu3Al/Ph3CB(C6F5)4 cocatalyst systems towards propylene polymerization was investigated under atmospheric pressure at 25 °C. The Ti complex produced ultrahigh‐molecular‐weight atactic poly(propylene), whereas Zr and Hf complexes formed high‐molecular‐weight isotactic poly(propylene)s via a site‐control mechanism. The isotactic poly(propylene) obtained with the Hf complex displayed a high melting temperature of 123.8 °C.
Bis(2,2′:6′,2″‐terpyrid‐4′‐yl) diethylene glycol was synthesized as a monomer unit and further utilized for polymerization with FeCl2 in order to form water‐soluble coordination polymers. Viscosity measurements and film‐forming properties indicate the formation of linear coordination polymers or larger ring structures. The terpyridine/iron(II) complexes are stable up to temperatures of 210 °C, but can be uncomplexed by the addition of an excess of a strong competitive ligand (HEDTA) under mild conditions.
Amphiphilic star‐shaped oligo(ethylene glycol)s with a hydrophobic bile acid core and varying number of hydrophilic arms have been made. Their thermal behavior in aqueous solutions depends on the number rather than the length of the arms. The two‐armed lithocholate derivative showed the strongest tendency for association and exhibited the lowest cloud point (79 °C) of the oligomers made, as well as another phase separation at a lower temperature (31 °C). The “double thermosensitivity” arising both from the salt‐dependent LCST of the oligo(ethylene glycol) segments and the temperature‐responsive self‐assembly of amphiphilic bile acid derivative provides an interesting path in the design of bile acid‐based smart materials.
The amphiphilic PEG1500‐b‐EM AP‐b‐PEG1500 (EM PAP) triblock copolymer of poly(ethylene glycol) (PEG) and emeraldine aniline‐pentamer (EM AP) in its concentrated solution can self‐assemble into a special shape like “sandglass”, as observed by transmission electron microscopy (TEM), field emission scanning electron microscopy (ESEM) and atomic force microscopy (AFM). This “sandglass”‐shaped assembly is composed of several “rods” aggregated in the middle, with every “rod” being about 8 µm in length and 300 nm in diameter. We conclude that the special “sandglass”‐shaped assembly may come into being because of the inducement effect of the crystallization of EM AP segments, by studying electron diffraction (ED) results and wide‐angle X‐ray diffusion (WAXD) characterization of the EM PAP triblock copolymer.
A novel experimental technique to follow the crystallization processes of poly(propylene)/MWCNT composites that experience a steady shear deformation using dynamic melt rheometry is described. The effects of heterogeneous nucleation, temperature, and preshear on the crystallization behaviors were determined. A quantitative evaluation of crystallization kinetics difference between quiescent and preshear conditions could be achieved. By combining rheology with POM, we demonstrate that two different crystallization processes account for the shear‐enhanced crystallization at low and high temperatures, respectively.
Self‐doped sulfonated polyaniline (PSA) has been synthesized on the surface of micellar nanoparticles made from positively charged surfactants by biocatalysis. The conformation forced by the electrostatic charge interactions between the positively charged micelle and the negatively charged PSA increases the conductivity of the PSA by three orders of magnitude. The pure PSA recovered from ion exchange, however, shows quite similar electrical properties compared with sulfonated polyanilines reported earlier. The increased conductivity of PSA complexes is as a result of the increased charge carrier concentration caused by a certain conformational locking.
The preparation of novel highly water‐soluble electrostatic complexes from C60‐anchored multi‐armed poly(acrylic acid)s and cationic porphyrin derivatives was demonstrated. The UV‐vis absorption and photoluminescence (PL) of these complexes show that the absorption of soret band exhibits a remarkable red shift and the emission of the Q band indicates an apparent quenching effect in comparison with that of the parent cationic porphyrin. These results imply a remarkable ground state and excited state interaction between the porphyrin ring and the C60 moiety.
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.
A triblock amphiphilic macrocycle consisting of a macrocyclic aromatic segment, a hydrophilic oligo(ethylene oxide) branch, and a hydrophobic alkyl dendron is successfully synthesized and characterized. The resulting cyclic amphiphile is observed to self‐assemble into hollow double‐layered capsules in aqueous solution, as confirmed by dynamic light scattering and cryogenic transmission electron microscopy investigations. The capsules are able to encapsulate hydrophobic guest molecules through aromatic interactions with high stability.
End‐group analyses of the oligo‐ and polypropylenes produced with bis(phenoxy‐imine) Zr and Hf complexes with methylaluminoxane (MAO) indicate that the polymerization is initiated by two consecutive 1,2‐insertions and is terminated by a β‐H transfer following a 2,1‐insertion. Our data indicate that chain propagation occurs with prevailing 1,2‐regiochemistry but with considerable regioerrors, and with virtually no stereoselectivity.
The polymerization of propylene mediated by bis(phenoxy‐imine) Zr and Hf complexes with MAO. 相似文献
A new donor–acceptor polymer based on 9,9‐dioctylfluorene is synthesized and tested in organic photovoltaic devices. Results show that the polymer exhibits good solubility in a range of organic solvents and has a high hole mobility. When blended with a PC70BM acceptor and fabricated into a bulk heterojunction, photovoltaic devices having a maximum power conversion efficiency (PCE) of 6.2% and a peak external quantum efficiency of 74% are created. Such efficiencies are realized without any necessity for solvent additives or thermal annealing protocols.
