Summary: A cationic polymerization of isobutylene, isobutyl vinyl ether, ethyl vinyl ether, vinylcarbazole and α‐methylstyrene was induced by mixing with poly(vinylidene fluoride) (PVDF) powder. The polymerization was an exothermic reaction and gave a high yield. An electron was abstracted from the monomer by PVDF. By the abstraction of the electron, the monomer was converted to a cation radical which induced polymerization. The generation of the cation radicals of the vinyl ethers was confirmed by an ESR spin trapping method, although the cation radicals could be coupled immediately. The resulting polymer was isolated from PVDF (not grafted) and characterized by size exclusion chromatography, IR, UV‐Vis and NMR spectroscopy. The copolymerization of vinyl ethers or vinyl ether/vinylcarbazole was carried out successfully to obtain their random copolymer. PVDF is regarded as a reusable catalyst for cationic polymerizations.
Reaction mechanism of the cationic polymerization of iBVE. 相似文献
The preparation of biodegradable and positively charged graphene–polymer nanocomposite for DNA uptake and release is presented. A pyrene‐terminated poly(2‐(dimethylamino) ethyl acrylate) is firstly synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization, followed by the attachment onto the graphene surface via the π–π stacking interaction. The positively charged polymer brushes benefit the uptake of the negatively charged DNA fragment via static interaction and the built‐in disulfide linkage between the polymer chain and graphene surface allows the biodegradable release of DNA in the presence of reducing agents. X‐ray photoelectron spectroscopy manifests the binding of DNA molecules to the polymer chains and agarose gel electrophoresis confirms the release of DNA.
Water‐soluble copolymers from mono‐1‐alkyl itaconates and N‐vinyl‐2‐pyrrolidone are synthesized and characterized. The mono‐1‐alkyl itaconates are prepared from itaconic anhydride and the related alcohol: 1‐dodecanol, 1‐octadecanol, 1‐docosanol, and 1‐triacontanol. The mono‐1‐triacontyl itaconate is synthesized from plant growth regulator policosanols extracted from Agave fourcrouydes, where 1‐triacontanol is the major product. The reactivity ratios, calculated according to the Mao‐Huglin method for copolymerizations conducted to medium‐high conversions, indicate a tendency toward alternation for all copolymerization reactions. Water solubility of copolymers is provided as a function of copolymer composition and aliphatic chain length.
A novel method for the synthesis of alkoxyamines that are subsequently used as initiator/regulators for NMP is reported. This method can be applied to low‐molecular‐weight olefins as well as to macromolecules containing alkene moieties to form poly(alkoxyamines). The reaction sequence comprises hydroboration of olefins with catecholborane followed by oxidation of alkylborane intermediates using nitroxides in the presence of methyl vinyl ketone to ultimately yield alkoxyamines that serve as suitable initiators for NMP. The first application of these alkoxyamines for the preparation of comb and star polymers is presented.
A series of multiarmed and multicomponent miktoarm (μ‐) star polymers have been successfully synthesized by developing a new iterative methodology based on a specially designed linking reaction of the block copolymer in‐chain anions, whose anions are positioned between the blocks, with α‐phenylacrylate (PA)‐functionalized polymers. The iterative methodology involves the following two reaction steps: a) introduction of two different polymer segments by the linking reaction of a block copolymer in‐chain anion with a PA‐functionalized polymer and b) regeneration of the PA reaction site. By repeating this reaction sequence, two different polymer segments are advantageously and successively introduced into the μ‐star polymer. In practice, repetition of the reaction sequence affords well‐defined 3‐arm ABC, 5‐arm ABCDE, 7‐arm ABCDEFG, and even 9‐arm ABCDEFGHI μ‐star polymers, composed of polystyrene, polystyrenes substituted with functional groups, polyisoprene, and poly(alkyl methacrylate) arms, respectively.
Summary: A water‐soluble diblock copolymer composed of poly(ethylene glycol) (PEG) and a cylindrical poly(acrylic acid) (PAA) brush is reported. It is prepared by a ‘grafting from’ approach using stepwise atom transfer radical polymerization combined with group transformation. Uniform molecular brushes, PEG113‐b‐P(MA‐g‐PAA26)169, are thus prepared as indicated by atom force microscopy analysis. This PAA densely grafted polymer is used to induce the crystallization of calcium carbonate in aqueous solution. Different experimental conditions, fast mixing reactions and static diffusion methods, are applied to explore the effect of polymer brushes on the crystallization, which is characterized by scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis.
AFM image of the polymer brushes on mica and an SEM image of CaCO3 particles prepared in its presence. 相似文献
The thermo‐adjustable hydrophilic/hydrophobic properties of AB, ABA and BAB block copolymers in which A is poly(methyl vinyl ether) (PMVE) and B is poly(isobutyl vinyl ether) (PIBVE) have been investigated. The block copolymers were prepared by “living” cationic polymerization using sequential addition of monomers. The polymerizations were carried out with the system acetal/trimethylsilyl iodide as initiator and ZnI2 as activator. The initiating system based on diethoxyethane leads to AB block copolymers whereas the initiating system based on tetramethoxypropane leads to ABA or BAB triblock copolymers. Well‐defined block copolymers of different composition with controlled molecular weights up to approx. 10 000 have been prepared. When IBVE is added to living PMVE, PIBVE‐blocks form only in the presence of an additional amount of ZnI2, which is attributed to the fact that part of the ZnI2 is inactive because of complex formation with PMVE. At room temperature, the combination of hydrophilic (PMVE) and hydrophobic (PIBVE) segments provides the copolymers with surfactant properties. Above the lower critical solution temperature (LCST) of PMVE, situated around 36 °C, the PMVE‐blocks become hydrophobic and the amphiphilic nature of the block copolymers is lost. The corresponding changes in hydrophilic/hydrophobic balance have been evaluated by investigation of the emulsifying properties of the block copolymers for water/decane mixtures as a function of the temperature. Below the LCST, the block copolymers have emulsifying properties similar to or better than those of the commercial PEO‐PPO block copolymers (Pluronic®). Either oil‐in‐water or water‐in‐oil emulsions can be obtained, depending on the polymer architecture and the water/decane volume ratio. The emulsifying properties are strongly reduced or completely lost above 40 °C. Emulsions obtained with a PMVE36‐b‐PIBVE54 block copolymer for a water/decane (v/v) ratio of 85/15 remained stable for more than six months.
50/50 and a 85/15 water/decane w/o emulsion (15 g/l) with the PMVE36‐b‐PIBVE54 block copolymer at 20 °C. 相似文献
A series of five fluorinated dithioesters PhC(S)SRCH2CnF2n+1 (where R represents an activating spacer and n = 6 or 8) was obtained in fair to high yields (57–88%). These transfer agents were successfully used in reversible addition‐fragmentation transfer (RAFT) of styrene (S), methyl methacrylate (MMA), ethyl acrylate (EA) and 1,3‐butadiene. Well‐chosen fluorinated dithioesters were able to lead to a good control of the radical polymerization of these monomers (i.e., molar masses of the produced polymers increased linearly with the monomer conversion and the polydispersity indexes ranging between 1.1 and 1.6 remained low). The relationship between the structures of the dithioesters and the living behavior of the radical polymerization of these above monomers is discussed and it is shown that the nature of the R group influences the living behavior from different contributions to radical stabilization. Furthermore, the RAFT process also yielded PMMA‐b‐PS and PEA‐b‐PS block copolymers bearing a fluorinated moiety. 相似文献
The mild environment where most proteins and antibodies in living systems are prepared has inspired fascination among chemists. Herein, a new, rapid, low‐cost, and environment‐friendly method is proposed to synthesize molecularly imprinted polymers (MIPs) via visible light activated reversible addition–fragmentation chain transfer polymerization in aqueous media at room temperature for highly selective electrochemical assay of glucose. The MIPs with microsphere morphology, the better hydraulic distribution, large surface area, uniform large pore sizes, and high pore volume exhibit a significant adsorption efficiency compared with nonimprinted polymers for glucose. In addition, the MIP sensor recognizing the glucose significantly exceeds that of the other saccharide analogs, possesses regenerative ability, and presents high sensitivity by applying for the detection of glucose in human urine samples. 相似文献
The preparation of novel nanoparticles is described, which consist of a poly(lactic acid) (PLA) core obtained by the nanoprecipitation method with a shell made of oppositely charged β‐cyclodextrin polymer (poly‐β‐CD) assembled using the layer‐by‐layer technique. Characterization of these nanoparticles is accomplished through dynamic light scattering, ζ‐potential measurements, X‐ray photoelectron spectroscopy and electron microscopy. The release of a loaded lipophilic molecule, benzophenone (BP), is mainly controlled by diffusion of BP and by its host–guest interaction with the β‐CD cavities of the adsorbed poly‐β‐CD. Increasing the number of poly‐β‐CD layers results in a better control of the release through the partition equilibrium between free BP and BP included in the cavities inside the multilayers.