A simple and direct method for derivatization of solid polysaccharides is presented. The novel methodology is based on the combination of organic acid‐catalyzed esterification or etherification and photochemical thiol‐ene click derivatization of a heterogeneous polysaccharide. The solid cellulose was “organoclick” modified with aryl, alkyl and polyester groups, respectively. The modification allows for a highly modular and metal free surface modification of solid polysaccharides.
Versatile synthetic methods towards a variety of thiophene‐nucleobase hybrid systems are reported. Adenine‐ and thymine‐based modified nucleosides characterized by a bithiophene unit linked to the C5′ or C8 position through an ethylenamino or an ethylensulfanyl bridge were synthesized and successfully polymerized in the presence of FeCl3. The self‐organization properties of the pure polymers as well as their mixtures ‐ with complementary nucleobases ‐ were investigated by means of optical microscopy and AFM in cast film showing complex supramolecular structures resulting from the interplay of multiple intermolecular interactions.
A series of size‐controlled, cyclic poly(tetrahydrofuran)s ( of 4 400–8 600) that consist exclusively of the monomer, i.e., oxytetramethylene, unit ( I ) have been prepared in high yield through the metathesis polymer cyclization of a telechelic precursor having allyl groups, 1 , in the presence of a Grubbs catalyst, and the subsequent hydrogenation of the linking, i.e., 2‐butenoxy, unit in the presence of an Adams' catalyst (PtO2). A remarkable topology effect has subsequently been observed upon the isothermal crystallization of these two model polymers, showing distinctive spherulite growth rates and spherulite morphologies in comparison with the relevant linear poly(tetrahydrofuran) counterpart that has ethoxy end groups ( II ).
The synthesis of branched macromolecules from renewable resources via olefin metathesis is described. We observed that it is possible to control the molecular weight during the acyclic triene metathesis (ATMET) of a triglyceride by the application of methyl acrylate as a chain stopper for this straightforward one step one pot polymerization. The resulting branched materials were characterized by GPC, NMR as well as ESI‐MS and the combination of these techniques provided valuable insights into the polymer structure as well as occurring side reactions during this olefin metathesis polymerization reaction.
A facile method for the synthesis of polyaniline–polypyrrole composite materials with network morphology is developed based on polyaniline nanofibers covered by a thin layer of polypyrrole via vapor phase polymerization. The hydrogen storage capacity of the composites is evaluated at room temperature exhibits a twofold increase in hydrogen storage capacity. The HCl‐doped polyaniline nanofibers exhibit a storage capacity of 0.46 wt%, whereas the polyaniline–polypyrrole composites could store 0.91 wt% of hydrogen gas. In addition, the effect of the dopant type, counteranion size, and the doping with palladium nanoparticles on the storage properties are also investigated.
Here we report for the first time on phosphorylation of cotton cellulose using baker's yeast hexokinase and phosphoryl donor adenosine‐5′‐triphosphate. An enzymatic assay was adopted for determination of the degree of phosphorylation of cellulose. This functional modification of cellulose resulted in improved colorability and flame resistance.
Phosphorylated glucopyranose unit of cellulose. 相似文献
Supramolecular poly(vinyl acetate) PVAc 3‐arms stars were successfully generated by Reversible Addition–Fragmentation chain Transfer (RAFT)‐polymerized chains bearing hydrogen‐bonding heterocomplementary associating units. Chain Transfer Agents (CTA) bearing thymine‐ and diaminopyridine‐based units were first synthesized and proved to mediate efficiently the polymerization of VAc. The binding ability of the chains in solution was then demonstrated by 1H NMR and GPC measurements, proving the formation of the supramolecular stars.
Computer simulations reveal the unique conformation of or erythro diisotactic polynorbornene, a polymer with numerous important applications in microelectronics. While previous simulations suggested that this polymer adopts a helix‐kink morphology, the results presented herein indicate that the reversal of the helix symmetry is the origin of such kinks which cause a transition from a rigid‐rod conformation to a random coil with increasing molecular weight. An RIS model was developed that accurately predicts the unique conformation of this polymer. This model predicts a rigid‐rod helical conformation that eventually transitions to a random coil at a degree of polymerization of approximately 500.
Melts of symmetric three‐arm stars are generated using a novel iterative method. In this method, an equilibrated low molecular weight configuration is used to generate progressively higher molecular weights by affine scaling and equilibration. At each stage in the progression, the synthetically lowered entanglement density allows bypassing of the exponentially large relaxation times of branched polymers. The quality of equilibration was assessed by measuring the mean dimensions, distribution of dimensions, and internal length scales of the polymers. The total time required to generate the progression of equilibrated configurations was seen to scale as the Rouse time of the highest molecular weight.
This article provides a comprehensive review of the synthesis, properties and applications of organometallic polymers of the transition metals. The different classes of organometallic polymers are described according to their structural make‐up, as well as by their methods of synthesis. A number of examples of each class are given to emphasize the richness and diversity in these areas of research. In addition to linear polymers, hyperbranched, crosslinked, star and dendritic polymers are also described. The properties that transition metal‐containing organometallic polymers possess, as well as the applications that these materials have found in various domains are highlighted.
Summary: Fabrication of honeycomb‐patterned films from amphiphilic dendronized block copolymer (PEO113‐b‐PDMA82) by ‘on‐solid surface spreading’ and ‘on‐water spreading’ method is reported. Highly ordered honeycomb films with quasi‐horizontally paralleled double‐layered structure can be fabricated by the on‐solid surface spreading method. This work raises the possibility that such structures can be formed in amphiphilic dendronized block copolymers and extends the family of source materials.
New aromatic compounds with a pyridazine core have been synthesized. Four electron‐withdrawing monomers have been easily prepared from simple condensation reactions and ring closure procedures. Optimized HOMO, LUMO, and bandgap energy levels have been obtained. The resulting conjugated polymers have been tested in organic solar cells. First studies have revealed power conversion efficiencies up to 0.5% for an active area of 1.0 cm2.
A novel top‐surface imaging process was successfully established using selective chemisorption of amine‐functionalized poly(dimethyl siloxane) onto the carboxylic groups formed on the surface of diazoketo‐functionalized polymer film by UV light irradiation. The chemisorbed poly(dimethyl siloxane) worked as an efficient etch mask for the subsequent oxygen plasma etching process for pattern generation. High‐resolution patterns were resolved with the new imaging process.
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.
A new concept to build shape memory polymers (SMP) combining outstanding fixity and recovery ratios (both above 99% after only one training cycle) typical of chemically crosslinked SMPs with reprocessability restricted to physically crosslinked SMPs is demonstrated by covalently bonding, through thermoreversible Diels–Alder (DA) adducts, star‐shaped poly(ε‐caprolactones) (PCL) end‐functionalized by furan and maleimide moieties. A PCL network is easily prepared by melt‐blending complementary end‐functional star polymers in retro DA regime, then by curing at lower temperature to favour the DA cycloaddition. Such covalent network can be reprocessed when heated again at the retro DA temperature. The resulting SMP shows still excellent shape memory properties attesting for its good recyclability.
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.
Furan ring‐functionalized solid surfaces are achieved by the initiated chemical vapor deposition (iCVD) method, a solvent‐free process to form films under mild conditions. The polymerization of furfuryl methacrylate monomer is initiated by a resistively heated filament wire. The functionality of the furan group in the iCVD film enabled Diels–Alder chemistry with 4‐phenyl‐1,2,3‐triazolin‐3,5‐dione (N‐PTD).
Well‐defined poly(ethylene oxide)s (PEOs) bearing reactive sites regularly distributed along the chain have been synthesized by the polycondensation of PEO containing a central tertiary amino group with dichloromethane, followed by quaternization with suitable reagents to obtain polyzwitterionic or cationic PEOs with alkyl, allyl, or fluorocarbon pendant groups. The pendant allyl groups have been converted into primary amino groups by reaction with 2‐aminoethanethiol hydrochloride to obtain polyamino‐functionalized PEO.
Polyfunctional PEOs bearing different pendant groups. 相似文献
We demonstrate the utility of soft X‐ray spectromicroscopy to simultaneously image the surface and bulk composition of polymer blend thin films. In addition to conventional scanning transmission X‐ray microscopy that employs a scintillator and photomultiplier tube to measure the transmitted X‐ray flux, channeltron detection of near‐surface photoelectrons is employed to provide information of the composition of the first few nanometers of the film. Laterally phase‐separated blends of two polyfluorene co‐polymers are studied, with the structure of both wetting and capping layers clearly imaged. This new information provides insight into the connectivity of bulk and surface structures that is of particular relevance to the operation of such blends in optoelectronic devices.
