A novel redox‐induced shape‐memory polymer (SMP) is prepared by crosslinking β‐cyclodextrin modified chitosan (β‐CD‐CS) and ferrocene modified branched ethylene imine polymer (Fc‐PEI). The resulting β‐CD‐CS/Fc‐PEI contains two crosslinks: reversible redox‐sensitive β‐CD‐Fc inclusion complexes serving as reversible phases, and covalent crosslinks serving as fixing phases. It is shown that this material can be processed into temporary shapes as needed in the reduced state and recovers its initial shape after oxidation. The recovery ratio and the fixity ratio are both above 70%. Furthermore, after entrapping glucose oxidase (GOD) in the system, the material shows a shape memory effect in response to glucose. The recovery ratio and the fixity ratio are also above 70%.
Three‐dimensional mesoscopic morphologies and the thermodynamics of structural phase transitions of amphiphilic lipids at air‐water interfaces are studied using self‐consistent field theory. Changing the relative amount of lipids in the system led to a series of 3D morphologic phases with varying average interfacial area per molecule, mimicking a compression of the model membranes. Membranes of both saturated and unsaturated lipids undergo a transition from cylindrical micelle to lamella when the lipid content in the system increases from 2% to about 19–20%. With further increase in the lipid content, saturated lipids first develop non‐uniform quasi‐2D distributions in the lamella and then gradually transform into a hybrid morphology containing quasi‐planar lamellae. In contrast, unsaturated lipids develop reverse‐micellar morphologies.
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.
Summary: A chitosan‐hydroxybenzotriazole (HOBt) aqueous solution prepared by simply mixing chitosan and HOBt in water provides an effective system to functionalize chitosan in an aqueous environment. This aqueous solution in combination with water‐soluble carbodiimide (WSC) allows the conjugation of functional groups onto chitosan under mild conditions without requiring any organic solvents or acid and heat. In this contribution, a series of model reactions that use a novel water‐based system of chitosan to functionalize the polymer with boc‐L ‐phenylalanine, poly(ethylene glycol) methyl ether, and dicarboxylated poly(ethylene glycol) is demonstrated.
Chitosan‐HOBt is effectively conjugated with R‐COOH via a water‐soluble carbodiimide (WSC) conjugating agent. 相似文献
An amylose‐grafted chitosan has been synthesized by a chemoenzymatic method according to the following two reactions. First, maltoheptaose is introduced to chitosan by a reductive amination using sodium cyanotrihydroborate in a mixed solvent of 1.0 mol · L−1 aqueous acetic acid and methanol at room temperature to produce a maltoheptaose‐grafted chitosan that has a well‐defined molecular structure. A phosphorylase‐catalyzed enzymatic polymerization of α‐D ‐glucose 1‐phosphate is then performed from the maltoheptaose‐grafted chitosan to obtain the amylose‐grafted chitosan. This material does not dissolve in any solvent, e.g., aqueous acetic acid and dimethyl sufoxide, which are good solvents for chitosan and amylose, respectively.
Summary: A protection‐graft‐deprotection method was developed to prepare chitosan‐g‐polycaprolactone graft copolymers, during which the ring‐opening copolymerization of ε‐caprolactone onto phthaloylchitosan (PHCS) happened without any additional catalysis. The intermediate PHCS was introduced primarily to protect the active amino group of chitosan. After controlled experiments, the phthalimido compound was proposed to be a novel kind of organic catalyst for the ring‐opening polymerization of caprolactone monomers, while the hydroxyl group acted as an initiator. Hence, in this graft system, PHCS was endowed with both self‐catalysis and self‐initiation at the same time, and the PCL side chains grew from the hydroxyl groups of the chitosan backbone.
Summary: Tetraaniline‐block‐poly(L ‐lactide) diblock oligomers are synthesized via ring‐opening polymerization. The diblock oligomers cast from an L ‐lactide selective solvent (chloroform) show spherical aggregates for the leucoemeraldine state, and ring‐like structures that are composed of much smaller spherical aggregates for the emeraldine state. The formation mechanisms of the two different surface morphologies are discussed in detail.
Surface morphology changes induced by oxidation of the aniline segment of tetraaniline‐block‐poly(L ‐lactate) and drying effects. 相似文献
The synthesis of new star‐shaped polymers, prepared by atom transfer radical polymerization of methyl methacrylate with tris(dialkylaminostyryl‐2,2′‐bipyridine) zinc(II) and iron(II) metalloinitiators, is reported. Their thermal and optical (absorption and emission) properties are discussed.
2,5‐Bis(chloromethyl)‐1,3,4‐oxadiazole was synthesized and dehydrohalogenation of this model compound was investigated under various base conditions. The formation of an intermediate with quinodimethane‐type structure is suggested for reaction in EtONa/EtOH. Polymerization of this intermediate proceeds via an anionic mechanism to form poly(1,3,4‐oxadiazole‐2,5‐diyl‐1,2‐vinylene). Polymerization at a toluene/water interface results in shorter polymerization times, milder conditions, higher molecular weights, higher yields and fewer defects in the polymer as compared to the corresponding polycondensation route.
Au nanoparticles (NPs) and polymer composite particles with phase‐separation structures were prepared based on phase separation structures. Au NPs were successfully synthesized in amphiphilic block‐copolymer micelles, and then composite particles were formed by a simple solvent evaporation process from Au NPs and polymer solution. The phase separated structures (Janus and Core‐shell) were controlled by changing the combination of polymers having differing hydrophobicity.
Sixteen parallel polymerization reactions of 2‐ethyl‐2‐oxazoline have been performed at different temperatures in an automated synthesizer that allowed individual heating of each reactor. During the reactions samples were taken automatically, which were characterized by means of both online GPC and offline GC, in order to optimize the reaction temperature and to determine the activation energy of the polymerization.
Fully conjugated block copolymers containing 1,4‐ and 1,3‐phenylenevinylene repeating units can be prepared by the sequential ring opening metathesis polymerization of strained cyclophanedienes, initiated by ruthenium carbene complexes (Grubbs metathesis catalysts). The molecular weight of the constituent blocks can be tightly controlled by changing the catalyst to monomer ratio and the volume fraction of the block copolymers independently tailored by the ratio of the monomers employed. Extensive phase separation between the constituent blocks is observed in thin films of these polymers by atomic force microscopy and efficient energy transfer between blocks containing 1,4‐ and 1,3‐phenylenevinylene units can be seen in the photoluminescence of these materials.
The compounds 2‐thioxanthone‐thioacetic acid and 2‐(carboxymethoxy)thioxanthone, bimolecular photoinitiators for free radical polymerization, are synthesized and characterized. Their capability to act as initiators for the polymerization of methyl methacrylate was examined. The postulated mechanism is based on the intermolecular electron‐transfer reaction of the excited photoinitiator with the sulfur or oxygen atom of the ground state of the respective photoinitiator followed by decarboxylation. The resulting alkyl radicals initiate the polymerization.
Micro‐Raman spectroscopy has been used to investigate the chemical micro‐heterogeneity of multiphase‐separated poly(ether urethanes) (PETU). Analysis of PETU cross‐sections by means of micro‐Raman spectroscopy revealed the nearly complete absence of soft segments in AI aggregates (called globules). These aggregates are in the order of a few micrometers in size. The composition of the matrix and the AII aggregates (spherulites) was comparable.
Example of an AFM image (sample 706, scan size 25 μm, converted to monochromatic image). 相似文献
Summary: The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine (PhOZI) with methyl tosylate (MeOTs) and butyl iodide (BuI) as initiators were performed in refluxing butyronitrile. Reaction kinetics under microwave irradiation was compared with conventional oil bath heating. The polymerization rates, under microwave irradiation, showed an acceleration by a factor of 1.8 (independently from the used initiator). The investigation of the thermal properties of the obtained poly(N‐benzoyl‐trimethyleneimine) showed the influence of molecular weight and end‐groups on the glass transition temperature.
The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine performed in refluxing butyronitrile. 相似文献
