Organic π‐conjugated polymers have emerged as one of the most fascinating classes of materials as they have found utility in a host of plastic electronics technologies. The distance between π‐systems and their relative orientation dictate energy/charge transfer, conductivity, and photophysical properties of these materials in bulk. This Feature Article discusses π‐conjugated polymers and model compounds in which specific inter‐π‐system interactions are covalently enforced and the effect that the scaffolding has on optoelectronic properties.
Summary: Poly(3‐alkoxythiophene)s with different degrees of regioregularity were prepared using three different methodologies. It is shown that their Faraday rotation is highly dependent on the degree of regioregularity. The origin of the differences in regiospecificity of the methodologies is discussed.
Chitosan grafted oligo(L ‐lactic acid) copolymers with different length of side chain were prepared through the reaction of terminal aldehyde group of oligo(L ‐lactic acid) (OLLA) and amino groups of chitosan. The mean molecular mass of the grafting OLLA chain was ca. 600 ～ 5 000. The graft copolymers are soluble in DMSO, DMF and acetic acid. The synthesis method and structure described here provide chitosan‐g‐OLLA copolymers with broad applicability.
Structure of chitosan‐g‐oligo(L ‐lactic acid). 相似文献
The Michael reaction of chitosan with acrylic acid was carried out successfully, even in water alone as the reaction medium. As a consequence of its good solubility in water, the reaction product, N‐carboxyethylchitosan, showed excellent biodegradable properties with standard activated sludge.
Polymerizations of vinyl ethers are carried out with (α‐diimine)nickel(II ) catalysts in the presence of methylaluminoxane. Effects of structural variations of the ligand on the activities of catalysts and polymer microstructure are described. The catalysts prepared by changing the bulkiness of ligand substituents in the ortho aryl position result in no specific trends terms of the yield and molecular weight of polymer. Poly(vinyl ether)s are atactic regardless of the structure of the catalyst used.
Summary: Oligo(acrylic acid)s, produced by RAFT polymerization, have been separated and analyzed for the first time by capillary zone electrophoresis. The resolution obtained by capillary electrophoresis in borate buffers is far higher than that currently achieved using size exclusion chromatography. This work demonstrates that capillary electrophoresis is the technique of choice for the characterization of oligomers of acrylic acid and of other water‐soluble monomers involved in emulsion polymerization processes.
Electropherograms of different acrylic acid (AA) oligomers obtained by CZE. 相似文献
The ability to control the dispersion of carbon nanotubes in polymers is key to most applications of nanotube‐polymer composites. This feature article describes recent advances in methods used to disperse carbon nanotubes and considers how these methods affect dispersion on different length scales. It is becoming increasing clear that perfect dispersion is not desired for many applications, in particular for electrical conductivity, and controlling the dispersion is key for proper function of the composite in its intended application.
Branched poly(butyl acrylate) was obtained from pulsed‐laser polymerizations carried out in bulk and in solution between −16 and 60 °C. The predominantly short branches are formed by backbiting. The Arrhenius temperature dependence of the backbiting rate is calculated, and the activation energy of this process was found to be remarkably higher than that of propagation. Branching thus increases with temperature leading to broader SEC traces and difficulties in the accurate determination of kp.
Arrhenius plot of kfp2 versus 1/T determined experimentally. 相似文献
Summary: We have successfully constructed a redox‐responsible hydrogel system by combination of β‐cyclodextrin (β‐CD), dodecyl‐modified poly(acrylic acid) [p(AA/C12)], and a redox‐responsive guest, ferrocenecarboxylic acid (FCA). In the reduced state of FCA, the ternary mixture exhibited a gel‐like behavior, whereas, in its oxidized state, the mixture exhibited a sol behavior.
Conceptual illustration for the redox‐responsive hydrogel system. 相似文献
4‐Vinylbenzoyl azide was synthesized from p‐vinylbenzoic acid and polymerized by free radical polymerization. The obtained polymer contained acyl azide groups which were thermally transformed to the corresponding isocyanato groups. Reactions on these polymers with ethanol, hydroxyethyl methacrylate and 1‐pyrenebutanol proceeded quantitatively. Time‐resolved FT‐IR studies of the reactions with ethanol were carried out by varying the concentration and temperature. The effect of the solvent polarity on the Curtius rearrangement was investigated.
An automated parallel synthetic approach has been developed for synthesizing polymer libraries by the Macromolecular Design via the Interchange of Xanthates (MADIX) process. The experimental set‐up, parallel polymerizations, characterization, and reproducibility tests are detailed. Examples of acrylic diblock copolymers synthesized in this way are given.
Automated MADIX polymerizations of BA in the presence of a X1 ‐capped PEA. 相似文献
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.
Chitosan is a weak cationic polysaccharide composed essentially of β(1 → 4) linked glucosamine units together with some N‐acetylglucosamine units. It is obtained by extensive deacetylation of chitin, a polysaccharide common in nature. Chitosan is a biocompatible, biodegradable, and nontoxic natural polymer that exhibits excellent film‐forming ability. As a result of its cationic character, chitosan is able to react with polyanions giving rise to polyelectrolyte complexes. Therefore, because of these interesting properties, it has become the subject of numerous scientific reports and patents on the preparation of microspheres and microcapsules. The techniques employed to microencapsulate with chitosan include, among others, ionotropic gelation, spray drying, emulsion phase separation, simple and complex coacervation, and polymerization of a vinyl monomer in the presence of chitosan. The aim of this work is to review some of the more common techniques used and to put forward the results obtained by our research group in preparing chitosan‐based microcapsules: for taste masking and improving the stability of a nutritional oil, the sustained release of drugs, as well as the preparation of chitosan superparamagnetic microcapsules for the immobilization of enzymes.
Scanning electron micrograph of some superparamagnetic chitosan particles and magnetic hysteresis loop of the microparticles. 相似文献
Rényi statistical entropy as a means to quantify mixing in two‐dimensional binary systems is presented. The use of Rényi entropies in defining the scale and intensity of segregation for mixing quality determination is analyzed. Finally, the relationship between the mixing process and the structures generated in the system is explored by using the Rényi entropy as an easy and computationally efficient method to calculate the system spectrum of fractal dimensions.
