Summary: Water‐soluble biomimetic chitosan derivative conjugating zwitterionic phosphorylcholine was efficiently prepared through Atherton‐Todd reaction under the mild conditions, and the possible formation mechanism of zwitterionic product was related to the nucleophilic attack of adjacent 3‐hydroxyl on the D ‐glucosamine residue to phosphorus with the help of base. UV absorption and melting behaviors of DNA/phosphorylcholine‐bound chitosan derivative showed that the phosphorylcholine‐bound chitosan derivative could be a new carrier for long‐circulating macromolecular drug delivery.
Poly(ethersulfone) membranes were surface modified in a one‐step procedure. For this purpose, the membranes were soaked with aqueous solutions of different low‐molecular weight molecules bearing diverse hydrophilic functionalities and subject to electron beam treatment. No catalysts, photoinitiators, organic solvents or other toxic reagents were used, and no additional synthetic or purification steps were required.
Highly functional and monodisperse macromolecules with tailored architecture constitute the key to designing efficient and smart nanomaterials. Dendrimers offer real potential to achieve this goal, and one of the earlier challenges faced by this novel class of polymers has been addressed by the evolution of synthetic methodologies. This review provides an evaluation of the role played by chemistry in taking these macromolecules of academic relevance to practical industrial and biological applications, in a relatively short period. One can now construct dendrimers in a ‘made‐to‐order’ fashion, for numerous applications in a variety of disciplines.
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.
A fast method is presented for the calculation of the MSD and the MWD of polymers obtained via step‐growth polymerization of polyfunctional monomers bearing identical reactive groups (i.e., systems of type “Afi”). Using this method, the complete distribution can be calculated rapidly, not just the statistical averages of the polymer population such as or . The computed MSD and MWD give more insight than these averages and can be compared to similar data measured on actual polymer systems. The low‐ and intermediate molecular size/weight part of the distribution curves are calculated using a recurrence scheme, while the high‐molecular tail (large and very large polymers) of the distributions is derived from an asymptotic approximation of the associated generating functions.
Different micromechanical models for the prediction of mechanical properties of CNT/polymer composites, taking into consideration filler percolation throughout the matrix, are considered. It is demonstrated that the critical filler volume fraction, where a percolating network of CNTs is forming, marks a “turning point” in the reinforcement efficiency. Expectations for the reinforcing effect of CNTs at concentrations above a percolating threshold with the current technology are in general unrealistic.
Summary: A water‐insoluble organic 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical is solubilized in aqueous solutions of aggregates of amphiphilic block copolymers with hydrophobic dendritic pendants. The number (100–200) of DPPH molecules solubilized in an aggregate, which is evaluated from UV‐visible absorption spectra, is in agreement with that of the DPPH radicals determined from electron paramagnetic resonance (EPR) spectroscopy. The DPPH radicals are stably solubilized without decomposition in the polymer aggregates. The radicals exhibit a single‐line EPR absorption, which is narrowed by the interspin interaction, and indicates the assembly formation of DPPH radicals in polymer aggregates. These results suggest the effective utilization of the DPPH radical as a spin‐probe indicator in aqueous solutions.
When DPPH is solubilized in aqueous solutions of NaAMPS‐b‐G2(n3), the polymer solutions become purple colored, which is characteristic of the DPPH radical. 相似文献
The preparation of polypyrrole/Fe3O4 nanospheres by a facile mini‐emulsion polymerization method is investigated using poly(ethylene glycol), poly(ethylene oxide), poly(vinyl alcohol), and hyaluronic acid as surfactants. Hyaluronic acid is deemed the most suitable surfactant since it results in well‐dispersed nanospheres of 80–100 nm, and offers the advantages of biocompatibility, cell adhesive property, and the availability of functional groups for attachment of other molecules. These polypyrrole/Fe3O4 nanospheres are magnetic and can be further functionalized with a cancer antibody, herceptin. Our results show that this combination of hyaluronic acid and herceptin results in high specific uptake of the nanospheres by cancer cells.
A novel approach is employed to produce core–corona nanospheres, which introduces a stereoregular hydrophilic part to an amphiphilic block copolymer. The resultant morphology is reported using isotactic‐poly(methacrylic acid)‐block‐poly(butyl acrylate). Infrared spectroscopy revealed a supramolecular interaction, and X ray diffraction revealed the crystallization of the outer isotactic‐poly(methacrylic acid) part. The nanostructure, which looks like a nanosized ‘grape’, was formed when nanospheres and nanofibers coexisted simultaneously and partially fused.
Summary: In this paper, unsaturated groups were introduced into poly(lactic acid) (PLA) for fabricating PLA‐based nanospheres with carbon‐carbon double bonds as functional groups. The morphology dependencies on fabrication conditions, including the fabrication time as well as the stirring rate, were also investigated.
SEM‐EDX image of poly(lactic acid) diacrylate nanospheres after exposure to osmium tetroxide vapor for 14 h. 相似文献
Green nanocomposite coatings based on renewable plant oils have been developed. An acid‐catalyzed curing of epoxidized plant oils with 3‐glycidoxypropyltrimethoxysilane produced transparent nanocomposites. The hardness and mechanical strength improved by incorporating the silica network into the organic polymer matrix, and good flexibility was observed in the nanocomposite. The nanocomposites showed high biodegradability.
Summary: The end coupling of living PSLi chains in hydrocarbon media by the addition of monoalkylbromides has been examined. A very selective PS–PS coupling reaction was obtained with neo‐pentylbromide (94%) at a ratio of PSLi/alkylbromide equal to 1 while the secondary and tertiary bromine derivatives yield only very limited coupling. The coupling mechanism is likely to involve a lithium‐bromine interchange at the PS chain end, generating polystyryl‐bromide which then reacts selectively with the remaining polystyryllithium chains.
The direct enzymatic polymerization of miniemulsions consisting of lactone nanodroplets represents a new and convenient pathway for the synthesis of biodegradable polymer nanoparticles, where the chemical composition and molecular weight can be varied in a certain range. Oligoesters completely end‐capped with an alkene or diene group can also be prepared by this technique. These building blocks extend polyester application as they allow to impart improved biodegradability to both siloxane and resin chemistry.
TEM image of the polyester particles obtained by enzymatic polymerization in miniemulsion. 相似文献
Summary: Phosphonate groups were introduced into block copolymers of styrene derivatives either as single end‐groups or as small blocks using nitroxide‐mediated radical polymerization. In order to combine the hydrophobic and hydrophilic segments, block copolymers with N,N‐dimethyl acrylamide were synthesized. After hydrolysis to phosphonic acid groups, adsorption of the polymer onto metal oxides was possible.
Conversion of the phosphonate groups by transesterification with trimethylbromosilane (TMBS), followed by hydrolysis of the silylester group. 相似文献
The effect of various alkylaluminium compounds and their mixtures on ethylene polymerization catalyzed with a tridentate bis(imino)pyridinyliron catalyst is studied. Triethylaluminium and trihexylaluminium are good cocatalysts but yield polyethylenes with broad molar mass distribution (MMD) whereas triisobutylaluminium, a less efficient activator, gives polyethylenes with unimodal and narrow MMD. Specific mixtures of branched and linear alkylaluminium compounds yield highly active catalytic systems and polyethylenes with unimodal and tunable MMD.
SEC traces of PE prepared with iron catalyst and (1) TEA, (2) TiBA, and (3) THA (Al/Fe = 250) as cocatalysts. 相似文献
Summary: Semiconducting polymers with moderate HOMO–LUMO energy gaps between 1.5 and 2.0 eV are of increasing attraction as donor components of bulk heterojunction‐type organic solar cells. The synthesis and characterization of a novel cross‐conjugated, aromatic polymer, poly(diindenonaphthalene) PDIN, with a HOMO‐LUMO gap of ca. 1.6 eV (λmax: 724 nm) in comparison to poly(indenofluorene) PIF, a previously described, structurally related polymer, is presented. The replacement of the central benzene ring of PIF by a naphthalene moiety in PDIN leads to an increase of the optical bandgap energy of ca. 0.16 eV.
