The morphology of a H‐shaped block copolymer (poly(ethylene glycol) backbone and polystyrene branches (PS)2PEG(PS)2) in a thin film has been investigated. A peculiar square lamella that has a phase‐separated microdomain at its surface is obtained after spin coating. The experimental temperature plays a critical role in the lamellar formation. The copolymer first self‐assembles into square lamellar micelles with an incomplete crystalline core due to the crystallizability of PEG. In the subsequent process of solvent evaporation, phase separation between PS and non‐crystalline PEG attached at the chain‐folded PEG surface takes place, which results in phase‐separated microdomains being formed at the lamellar surface.
Summary: An initiator for nitroxide mediated ‘living’ free radical polymerization was prepared with a fluorescent tag attached to the initiating alkyl radical terminus. This was used to synthesize amphiphilic poly(acrylic acid)‐block‐polystyrene diblock copolymers, which self assembled in a tetrahydrofuran/buffer solution to form structures that are visible by fluorescence.
In this communication, the synthesis, characterization, and properties of highly conductive core–shell nanocomposites of poly(N‐vinylcarbazole) (PNVC)–polypyrrole (PPY) copolymers with multi‐walled carbon nanotubes (MWCNTs) are described. A unique free‐radical coupling reaction between PNVC and PPY cation radicals in chloroform solvent, using feric chloride as an oxidant, in the presence of suspended MWCNTs in the reaction medium, was used for the synthesis of nanocomposite. Field‐emission scanning and transmission electron microscopy studies showed the formation of the core–shell nanocomposite. Raman spectrocopy results as well as thermogravimetric analysis supported the electron microscopic observations. The resulting PNVC–PPY copolymer‐coated MWCNTs showed an unprecedentedly increased value of direct electrical conductivity (bulk) compared to the conductivity of all samples even with pure MWCNTs.
A template‐free method for the production of polypyrrole nanofibers is presented. By adding a small amount of bipyrrole into the oxidative polymerization of pyrrole, a drastic change in the morphology of the observed material is observed from large, granular particles to nanofibrils with an average diameter of 20 nm. This simple procedure allows for the production of polypyrrole nanofibers without the presence of surfactants or other structural directing agents. The polypyrrole nanofibers can form stable water dispersions which can be cast into films of sufficient quality to function as chemical sensors for analytes such as ammonia.
The synthesis of water soluble star‐block copolypeptides and their encapsulation properties are described. The star‐block copolypeptides, obtained by ring‐opening polymerization of amino acid N‐carboxyanhydrides, consist of a PEI core, a hydrophobic polyphenylalanine or polyleucine inner shell, and a negatively charged polyglutamate outer shell. The encapsulation study showed that these water soluble, amphiphilic star‐block copolypeptides could simultaneously encapsulate versatile compounds ranging from hydrophobic to anionic and cationic hydrophilic guest molecules.
Summary: Amphiphilic graft polyphosphazenes (EtTrp/PNIPAm‐PPP) with different mole ratios of hydrophobic groups to hydrophilic segments were synthesized by ring‐opening polymerization and subsequent substitution reactions. The self‐assembly behavior of these graft copolymers was studied in detail by TEM, SEM, CLSM, and AFM. Depending on the copolymer composition and common organic solvent employed in dialysis process, supramolecular aggregates ranging from network, nanospheres, high‐genus particles to macrophage‐like aggregates were produced with graft copolymers.
The hydroxyl end groups of poly(ethylene glycol) (PEG) have been transformed easily and quantitatively into amino groups via the Mitsunobu reaction. Phthalimide was alkylated with PEGs and the hydrazinolysis of the resulting phthalimido‐PEGs gave the amino compounds in high yields. Quaternization of the amino groups leads to hydrophilic polymer chains bearing a positive charge on one or two ends, depending on the chosen PEG. Such products can be used to protect sterically, negatively charged particles such as clays.
The synthesis of a rapidly forming redox responsive poly(ferrocenylsilane)‐poly(ethylene glycol) (PFS‐PEG)‐based hydrogel is described, achieved by a thiol‐Michael addition click reaction. PFS bearing acrylate side groups (PFS‐acryl) was synthesized by side group modification of poly(ferrocenyl(3‐iodopropyl)methylsilane) (PFS‐I) and characterized by 1H NMR, 13C NMR, and FT‐IR spectroscopy. The equilibrium swelling ratio, morphology, rheology, and redox responsive properties of the PFS‐PEG‐based hydrogel are reported.
A generalized silica coating scheme is used to functionalize and protect sub‐micron and micron size dicyclopentadiene monomer‐filled capsules and polymer‐protected Grubbs' catalyst particles. These capsules and particles are used for self‐healing of microscale damage in an epoxy‐based polymer. The silica layer both protects the capsules and particles, and limits their aggregation when added to an epoxy matrix, enabling the capsules and particles to be dispersed at high concentrations with little loss of reactivity.
Double helical microropes of polyvinylpyrrolidone (PVP) with diameters of less than 10 µm and lengths of up to 5 cm were fabricated using a new electrospinning technique. In contrast to the typical electrospinning set‐up, a negatively charged rotating collector tip was used in this work, so that the two jets from two positively charged spinnerets were induced to two bundles that met at the rotating collector tip, leading to the formation of microropes. The pitch of microropes could be monitored by simply adjusting the distance between the two spinnerets.
The copolymerization system of oxetane and tetrahydropyran is reinterpreted with the aid of computer simulations. The original claim that this system is a “living” and/or controlled pseudoperiodic copolymerization 1 is not confirmed by the simulation results. It is suggested that the formation of branched oxonium cations and the statistical nature of THP incorporation are the reasons for the observed discrepancies between the simulation results and experimental data.
Summary: Polymer nanospheres are synthesized by free‐radical dispersion copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) with a methacryloyl‐terminated polystyrene (PS‐MC) macromonomer in cyclohexane. Such polymer nanospheres are stabilized sterically with polystyrene (PS)‐grafted chains in cyclohexane at temperatures greater than 34 °C (the Θ temperature for PS). Ordered microporous surface films are constructed by casting these core‐shell‐type nanospheres from hot cyclohexane solution at 20 °C. The results indicate the possibility of fixation or encapsulation of functional materials after microporous patterning of the core‐shell‐type nanospheres.
SEM photograph of a vertical section of a hexagonal micropore film obtained here. 相似文献
Layer‐by‐layer (LbL) assembly was conducted on CaCO3 microparticles pre‐doped with polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA) micelles, and resulted in micelles encapsulation in the microcapsules after core removal. Distribution of the micelles in the templates and capsules was characterized by transmission electron microscopy and confocal laser scanning microscopy. The micelles inside the capsules connected with each other to form a chain and network‐like structure with a higher density near the capsule walls. The hydrophobic PS cores were then able to load small uncharged hydrophobic drugs while the negatively charged PAA corona could induce spontaneous deposition of water‐soluble positively charged drugs such as doxorubicin.
A trithiocarbonate RAFT agent was modified with a pyridyl disulfide group and used in the direct synthesis of endgroup pyridyl disulfide‐functionalized homo‐ and amphiphilic block copolymers of oligo(ethyleneglycol) acrylate (PEG‐A) and butyl acrylate (BA). Both the homo‐ and copolymerizations were found to be well controlled via the RAFT mechanism. The NMR analysis indicated that both the homopolymers of PEG‐A and the amphiphilic diblock copolymers of PEG‐A and BA possessed pyridyl disulfide terminal groups. A UV‐Vis absorption test revealed that the pyridyl disulfide endgroup of the polymer could be efficiently used to couple thiol‐bearing molecules to the polymer without the need for any post‐polymerization modification. This communication presents the first efficient direct synthesis of thiol‐reactive endgroup‐functionalized well‐defined polymers via the RAFT technique.
Novel fullerene‐grafted poly(3‐hexylthiophene) (P3HT)‐based rod‐coil block copolymers have been synthesized. The regioregular P3HT rod block has been synthesized by a modified Grignard metathesis reaction (GRIM). An original in situ end‐capping reaction has been developed in order to convert the P3HT block into an efficient macro‐initiator for the nitroxide‐mediated radical polymerization (NMRP) of the coil block. Controlled radical polymerization of the second poly(butylacrylate‐stat‐chloromethylstyrene) [P(BA‐stat‐CMS)] block has been done through various conditions leading to different coil block lengths. The final electron donor‐acceptor block copolymer has been obtained after C60 grafting in soft conditions. Copolymers have been characterized by 1H NMR and size exclusion chromatography. Optical characterizations, before and after C60 grafting, are reported.
The stability and reactivity of mono‐ and multi‐protonatred N‐substituted isatin derivatives were studied at PBE0/aug‐cc‐pvtz//PBE0/6‐31+G** level of theory in triflic acid (TFSA) solution. Calculations showed that the monocationic intermediates are the principal reactive species in the reaction of hydroxyalkylation of isatin derivatives in TFSA media. Electron‐withdrawing substituents on the nitrogen atom increase the reactivity of isatin‐containing electrophiles towards aromatic hydrocarbons, in accordance with their expected electronic influence. Steric factors also play an important role in the reactivity of isatin‐containing electrophiles, especially in the second reaction step, due to their more sterically hindered reactive center.
A long alkylsilyl group was attached to a thiophene ring system to overcome the instability of 2,5‐bis(halomethyl)thiophene monomers, by imparting steric hindrance and electronic delocalization. The resulting stable monomer could be used directly to prepare low‐band‐gap poly(thienylenevinylene) (1.57 eV) through heteroaromatic dehydrohalogenation polymerization.
