共查询到20条相似文献,搜索用时 31 毫秒
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Miriam Fritsche Dieter W. Heermann Mariana Dutra Claudette E. Cordeiro 《Macromolecular theory and simulations》2010,19(7):440-448
By Monte Carlo simulations we provide insight into the isolated single‐ and double‐tethered (ST and DT) polymer chain attached to an impenetrable surface to elucidate open theoretical questions and guide future experiments investigating the impact of tethering on the genome packaging by concurrent visualisation of multiple loci along the chromosome(s). In the models, either one or both ends (at a grafting distance d) are fixed or the ST and DT chain are “annealed” by permitting the anchor(s) to diffuse laterally along the surface. We analyse chain self‐entanglement, intrachain segment correlations, the relationship between mean square physical distance and corresponding contour length and provide the first report on the diffusion behaviour.
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Sergey Vyazovkin Ion Dranca Xiaowu Fan Rigoberto Advincula 《Macromolecular rapid communications》2004,25(3):498-503
Summary: Thermogravimetry and differential scanning calorimetry have been used to study the thermal and thermo‐oxidative degradation of polystyrene (PS) and a PS–clay nanocomposite. An advanced isoconversional method has been applied for kinetic analysis. Introduction of the clay phase increases the activation energy and affects the total heat of degradation, which suggests a change in the reaction mechanism. The obtained kinetic data permit a comparative assessment of the fire resistance of the studied materials.
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Ryuji Sugi Akihiro Yokoyama Tsutomu Yokozawa 《Macromolecular rapid communications》2003,24(18):1085-1090
Well‐defined telechelic‐type aromatic polyamides having a secondary amino group and a phenyl ester moiety at each chain end were prepared by the chain‐growth polycondensation of phenyl 4‐(octylamino)benzoate ( 1 ) with initiator 2 (N‐tert‐butoxycarbonylated 1 ), followed by deprotection of the N‐protecting group of the initiator unit. This polycondensation was applied to the synthesis of well‐defined di‐ and triblock copolymers of aromatic polyamides and poly(tetrahydrofuran) (poly(THF)) by the reaction of the terminal secondary amino group of the polyamide with the living cationic propagating group of poly(THF).
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Miniemulsion polymerization with an amphiphilic poly(acrylic acid)‐block‐polystyrene reversible addition–fragmentation chain transfer agent as a surfactant and polymerization mediator is used to synthesize highly uniform nanocapsules. The nanocapsules with uniform structures, which include particle size, shell thickness, and shape symmetry, could be achieved by the post‐addition of a small amount of sodium dodecyl sulfate. Although the solid particles seem unavoidable, the ‘pure’ uniform core–shell structures are easily collected by centrifugation.
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Amilton Martins dos Santos Jordan Pohn Muriel Lansalot Franck D'Agosto 《Macromolecular rapid communications》2007,28(12):1325-1332
Hydrophilic (co)polymers carrying a thiocarbonyl thio end group such as poly(dimethylaminoethyl methacrylate), poly(ethylene oxide), and poly(ethylene oxide)‐block‐poly(dimethylaminoethyl methacrylate) have been evaluated as precursors of stabilizers in batch ab initio emulsion polymerization of styrene under acidic conditions to form electrosterically stabilized polystyrene latex particles. As a mixture of P(DMAEMA/H+Cl−)‐RAFT and PEO‐RAFT failed to give satisfactory results, PEO‐RAFT was used as a control agent for the RAFT polymerization of DMAEMA, and the resulting block copolymer was successfully used in ab initio styrene emulsion polymerization.
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Roberto Napolitano 《Macromolecular theory and simulations》2006,15(8):614-618
Summary: A comparison between the crystal structure of isotactic cis‐1,4‐poly(1,3‐pentadiene) previously predicted by molecular mechanics calculations and that successively determined by other authors by experimental data is reported. The agreement between the two structures is very good as far as the space group, the unit cell parameters and the conformation of the polymer chain are concerned. The mode of packing of the chains proposed in the experimental crystal structure is very similar to that found as relative minimum in the previous energy calculations. The coexistence, in different amounts, of these two modes of packing is suggested by the analysis of the simulated X‐ray spectra and by the results of new energy calculations.
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Well‐defined PEO‐b‐PMMA was prepared, initiated by macroinitiator PEO‐Br, by means of ATRP, where esterification of the terminal hydroxyl group of PEO with 2‐bromoisobutyryl bromide yielded a macroinitiator PEO‐Br. Highly ordered microporous films (hexagonal pattern) were constructed by emulsion micelles of such amphiphilic diblock copolymer formed from a solution with CHCl3/H2O/THF = 100:5:10 (v/v). We also constructed the microporous films using diblock copolymer by the current water‐assisted method.
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Luis Arzondo J. Pablo Tomba Jos M. Carella Jos M. Pastor 《Macromolecular rapid communications》2005,26(8):632-636
Summary: We explored the diffusion mechanisms in a series of liquid/glassy polymer interphases. The diffusion experiments were performed in a unique way: the temperature range studied encompassed the glass transition temperature (Tg) of the glassy matrices. We observed that the diffusion behavior of the liquid polymer was remarkably continuous when passing through the matrix Tg, and that the diffusion modes at the liquid/glassy interphases were very similar to those observed in liquid/liquid polymer diffusion.
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Akinori Fujinami Shigenobu Ogata Hajime Kimizuka Yoji Shibutani 《Macromolecular theory and simulations》2008,17(9):488-495
The large‐deformation energetics of a single molecular chain of the rod‐like polyimide PMDA‐PDA was investigated using DFT, ab initio MO and semi‐empirical MO methods. The force/displacement curves were calculated from tensile testing simulations along the axis of the molecular chain, allowing a discussion of the distribution and change of local strain of the molecular chain. The deformation behavior of a single PMDA‐PDA molecular chain under finite deformations as functions of bending angle and dihedral angle between PMDA and PDA groups are compared. It is found that the semi‐empirical MO calculations provide sufficient accuracy to express the energetics of large deformations except for compressive deformation.
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Mehmet Atilla Tasdelen Mustafa Uygun Yusuf Yagci 《Macromolecular rapid communications》2011,32(1):58-62
Well‐controlled radical polymerization of methyl methacrylate can be achieved by in situ photochemical generation of copper (I) complex from air‐stable copper (II) species without using any reducing agent at room temperature. The living character of this polymerization was confirmed by both the linear tendency of molecular weight evolution with conversion and a chain extension experiment.
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Summary: A unified model is developed for the finite size‐effect on the glass‐transition temperature of polymers, Tg(D), where D denotes the diameter of particles or thickness of films. In terms of this model, Tg depends on both the size and interface conditions. The predicted results are consistent with the experimental evidence for polystyrene (PS) particles and films with different interface situations.
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Guicun Li Hongrui Peng Yi Wang Yong Qin Zuolin Cui Zhikun Zhang 《Macromolecular rapid communications》2004,25(18):1611-1614
Summary: Polyaniline nanobelts have been synthesized by a self‐assembly process using the chemical oxidative polymerization of aniline in a surfactant gel. The morphologies of polyaniline nanostructures were characterized by field‐emission scanning electron microscopy and transmission electron microscopy. The effects of the concentrations of cetyltrimethylammonium bromide on the morphologies of polyaniline nanostructures have also been investigated.
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Geoffrey Johnston‐Hall Christopher Barner‐Kowollik Michael J. Monteiro 《Macromolecular theory and simulations》2008,17(9):460-469
The reversible addition‐fragmentation chain transfer chain length dependent termination (RAFT‐CLD‐T) technique allows a simple experimental approach to obtain chain‐length‐dependent termination rate coefficients as a function of conversion, k(x). This work provides a set of criteria by which accurate k(x) can be obtained using the RAFT‐CLD‐T method. Visualization of three‐dimensional plots varying all kinetic rate parameters and starting concentrations demonstrates that only certain combinations give an accurate extraction of k(x). The current study provides hands‐on guidelines for experimentalists applying the RAFT‐CLD‐T method.
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Qianqian Li Gui Yu Jing Huang Haijie Liu Zhen Li Cheng Ye Yunqi Liu Jingui Qin 《Macromolecular rapid communications》2008,29(10):798-803
Two new “H” type of indole‐based chromophores were designed and successfully introduced to the polymeric system, the resultant polymers demonstrated enhanced NLO effects, good processability, thermal stability and nearly excellent transparency, indicating the advantages of “H” type chromophore moieties. And they could be promising candidates for the practical applications as new photonic materials.
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Poly(cyclooctene)s with pendant Alq3 and fac‐Ir(ppy)3 were synthesized. Carbazole‐based comonomers were used to increase the solubility of the polymers and to transfer the energy into metal complexes. Excitation spectra of all polymers provided evidence of energy transfer. We established that the polymer backbone does not interfere with the optical properties of the metal complexes. All copolymers retained the optical properties of their small molecule metal complex analogs in solution and the solid state, making these polymers promising materials for potential electro‐optical applications.