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1.
JinDong Han JianXun Ding ZhiChun Wang ShiFeng Yan XiuLi Zhuang XueSi Chen JingBo Yin 《中国科学:化学(英文版)》2013,56(6):729-738
Diethylamine, di-n-hexylamine, dicyclohexylamine and triethylamine have been used as initiators for the ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BLG NCA) to synthesize poly(γ-benzyl-l-glutamate) (PBLG). The relationship between the molecular weight of PBLG and the molar ratio of monomer and initiator was studied. With dicyclohexylamine as initiator, the influence of monomer concentration, and reaction temperature and time on the polymerization of BLG NCA was examined. Three reagents were used for the deprotection of benzyl groups in PBLG, including hydrobromic acid/acetic acid (33 wt.%), NaOH aqueous solution and trimethylsilyl iodide (TMSI). Through examining the molecular weight of PLGA obtained using different deprotection methods, it was revealed that TMSI could minimize chain cleavage in the process of deprotection and retain the degree of polymerization. The biocompatibilities of PBLG obtained using different initiators were evaluated by a live/dead assay against L929 fibroblast cells. The in vitro cytotoxicities of PLGA obtained using different deprotecting agents were evaluated by a methyl thiazolyl tetrazolium assay. The results revealed that both PBLG and PLGA exhibited good biocompatibilities. 相似文献
2.
Hiroshi Kamitakahara Akihiro Baba Arata Yoshinaga Ryo Suhara Toshiyuki Takano 《Cellulose (London, England)》2014,21(5):3323-3338
This article describes the first observation of crystallization-induced microphase separation in thin film and bulk cellulose triacetate-block-poly(γ-benzyl-l-glutamate) (PBLG) [cellulose triacetate (CTA)-b-PBLG] via copper-catalyzed azide–alkyne cycloaddition (CuAAC) between azido-functionalized CTA at the reducing end and alkyne-functionalized PBLG at the C-terminus. The reactivity of the amino group at the C-1 position of the glucosyl residue at the reducing end for the initiation reaction of the ring-opening polymerization (ROP) of γ-benzyl-l-glutamate N-carboxyanhydride was compared to that of the azido group at the reducing end of CTA for CuAAC, with PBLG bearing an alkyne group at the C-terminus. Although the amino group at the reducing end of CTA exhibited no reactivity as a macroinitiator for ROP of BLG, the azido group at the reducing end of CTA reacted with the alkyne group at the C-terminus of PBLG to afford CTA-b-PBLG. The structure of CTA-b-PBLG was characterized by 1H- and 13C-nuclear magnetic resonance spectroscopies, infrared spectroscopy, differential scanning calorimetry, and wide angle X-ray diffractometry. Microphase separation of the film and bulk of CTA-b-PBLG was clearly shown by atomic force microscopy, field-emission scanning electron microscopy, and transmission electron microscopy. 相似文献
3.
Yusuke Takahashi Hirotaka Fujita Wan-Hua Lin Yuan-Yao Li Takao Fujii Akiyoshi Sakoda 《Adsorption》2010,16(1-2):57-68
Through fine tuning of synthesis conditions, we successfully synthesized three types of carbon nanofiber (CNF) (herring-bone carbon nanofiber, platelet carbon nanofiber, and cup-stacked carbon nanofiber) by the thermal decomposition of a mixture of poly(ethylene glycol) (PEG) and nickel chloride (NiCl2). A series of experimental results demonstrated that the key factors for the selective synthesis of these CNFs were the (1) NiCl2/PEG ratio, (2) drying time of the polymeric mixture, (3) state of PEG (liquid or solid) before temperature rising, and (4) temperature profile during the thermal decomposition. Changes in these conditions contributed to the formation of Ni catalyst particles from the catalyst NiCl2 with different morphology, thereby resulting in the growth of different types of CNF or amorphous carbon products according to the catalyst particle’s shape. Also, we found that the mechanism of CNF growth in this synthesis method was fundamentally the same as that in chemical vapor deposition (CVD). 相似文献
4.
Simultaneous optical observation of anisotropic texture was performed under transient stress response in shear flow for a
concentrated solution of poly(γ-benzyl-l-glutamate) (PBLG). Transient stress of the PBLG solution immediately after the onset of the shear flow showed a remarkable
stress overshoot and damping oscillation behavior, followed by a steady state. On the other hand, simultaneous observation
of the polarized optical microscopy showed the remarkable distortion of the banded texture immediately after the onset of
the shear flow and the periodical changes in the retardation followed by a steady texture of the PBLG solution. The remarkable
stress overshoot and the damping oscillation are closely related to the distortion of the banded texture and to the changes
in the orientation of the rod-like molecules of the PBLG, respectively.
Received: 15 December 1999/Accepted: 12 July 2000 相似文献
5.
《Tetrahedron: Asymmetry》1998,9(11):1871-1881
We report the first visualization of chiral molecules oriented in a polypeptide liquid crystalline system (PBLG) using proton-decoupled natural abundance deuterium NMR. The chiral discrimination is observed through measurements of the quadrupolar splitting differences and we demonstrate that the sensitivity of natural abundance deuterium NMR is sufficient to measure the differential ordering effects (DOEs) without the need for isotopic enrichment. The feasibility and the potential of this novel method were investigated using a 5.87 T spectrometer (proton frequency 250 MHz). Several examples of chiral discrimination are presented and particular emphasis is given to demonstrate the potential of this approach. 相似文献
6.
《European Polymer Journal》1985,21(6):569-572
Polymerizations of 2-naphthyl methacrylate and 4(1-methylphenethyl)phenyl methacrylate (cumylphenyl methacrylate) have been carried out in solvents with different dielectric constants and donor numbers (DN). By means of 1H-NMR and fluorescence spectroscopy, the tacticities of the polymers were studied. It was found that the structures of the polymers depend on the dielectric constant of the solvent and not on its donor number. In solvents with high dielectric constant, the contents of isotactic triads are higher than for solvents with low dielectric constants. 相似文献
7.
Geik Ling Teoh Kong Yong Liew Wan A. K. Mahmood 《Journal of Sol-Gel Science and Technology》2007,44(3):177-186
Abstract Alumina nanofibers of high aspect ratio with surface area of >300 m2 g−1 has been prepared successfully in bulk quantities by the sol–gel method. The synthesis parameters including the binary water–alcohol
solvent system to aluminium isopropoxide ratio, pH, type of solvent and aging temperature affect the uniformity and formation
of nanofibers. It is proposed that alumina nanofibers were formed by the curling of the nanosheets upon condensation after
the hydrolysis. The phase evolution of alumina nanofibers from pseudoboehmite to α phase has been shown by XRD and FTIR. 27Al NMR investigations show that the Al atoms are six and four coordinated. The morphology of the alumina nanofibers does not
change much as the calcination temperature was increased. In addition, the average pore size increases and the BET surface
area decreases as a function of calcination temperature. The thermal behavior of alumina nanofibers was investigated by TGA.
Graphical Abstract
相似文献
8.
9.
A. A. Shcherbina V. K. Gerasimov T. P. Semenov A. E. Chalykh 《Russian Chemical Bulletin》2018,67(10):1831-1837
Phase behavior and structure formation was studied using optical interferometry, nephelometry, and refractometry in the polymer–solvent–nonsolvent system for DMF solutions of two poly(amic acids): based on 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride and meta-phenylenediamine (PAA-1) and pyromellitic acid dianhydride and 4,4′-oxydianiline (PAA-2). Distilled water and its mixtures with DMF were used as a nonsolvent. According to the results of the study, isothermal cross sections of the phase state diagram in the threecomponent system were plotted, the position of the critical point, the spinodal, and the conodes were determined, the movement of the figurative points in the system was traced depending on the nonsolvent composition. 相似文献
10.
V. Castelletto I. W. Hamley P. Holmqvist C. Rekatas C. Booth J. G. Grossmann 《Colloid and polymer science》2001,279(7):621-628
The structure and flow behaviour of a micellar “cubic” phase is studied, using small-angle X-ray scattering (SAXS) and constant
stress rheometry on a poly(oxyphenylethylene)–poly(oxyethylene) diblock copolymer in water. The predominant structure is a
face-centred cubic (fcc) array of spherical micelles, which under shear undergoes layer sliding to give a scattering pattern
from stacked hexagonal close-packed layers. A detailed analysis of the SAXS data indicates the presence of a fraction of grains
with a structure distorted from a fcc phase. The additional reflections that characterize this structure can be indexed to
a rhombohedral unit cell, space group R3ˉm, with the same volume as the fcc unit cell. The rhombohedral unit cell corresponds to a cubic cell that has been “stretched”
along a [111] direction, and it is suggested that such a structure results from the gradient in shear velocity in the Couette
cell employed. Shearing at high shear rates leads to a “smearing out” of the reflections, but upon cessation of shear under
these conditions a highly oriented SAXS pattern is obtained, which confirms the persistence of rhombohedral ordering. The
shear-induced changes in orientation are correlated to a plateau observed in the stress plotted against shear rate, such a
plateau being a sign of inhomogeneous flow.
Received: 8 September 2000 Accepted: 29 November 2000 相似文献
11.
In solutions in DMSO-d6, the products from the condensation of ethanolamine and 1,2- and 1,3-aminopropanols with aldoses are mixtures of the - and -pyranose forms, whereas the -mercaptoethylimines of aldoses have the 1,3-thiazolidine structure. Glucose -mercaptoethylimine is characterized by ring-chain tautomerism involving the -pyranose and diastereomeric 1,3-thiazolidine tautomers.Military-Medical Academy, St. Petersburg, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1068–1071, August, 1998. 相似文献
12.
13.
The nucleation and crystallization of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL) in the PEO/PCL blends have been investigated by means of optical microscopy (OM) and differential scanning calorimetry (DSC). During the isothermal or nonisothermal crystallization process, when the adjacent PEO is in the molten state, PCL nucleation preferentially occurs at the PEO and PCL interface; after the crystallization of the adjacent PEO, much more PCL nuclei form on the surface of the PEO crystal. However, PEO crystallizes normally and no interfacial nucleation occurs in the blend. The concentration fluctuation caused by liquid–liquid phase separation (LLPS) induces the motion of PEO and PCL chains through interdiffusion and possible orientation of chain segments. The oriented PEO chain segments can assist PCL nucleation, and the heterogeneous nucleation ability of PEO increases with the orientation of PEO chains. Oriented PCL chain segments have no heterogeneous nucleation ability on PEO. It is postulated that the interfacial nucleation of PCL in the PEO/PCL blend follows the combination of “fluctuation-assisted crystallization” and “interface-assisted crystallization” mechanisms. Figure
a Illustration of PEO and PCL segments orientation caused by interdiffusion at the interface with concentration fluctuation and PCL spherulite induced by oriented PEO chains. b Illustration of PCL spherulites induced by the surface of PEO spherulite. PEO-rich and PCL-rich domains form and grow toward the liquid–liquid coexistent compositions during LLPS. The moving PEO and PCL chains could induce some segmental alignment or orientation (relative to adjacent chains) during the reptative interdiffusion. The oriented PEO segments have the heterogeneous nucleation ability on PCL, leading to the PCL nuclei occurs at the interface of the phase domains, illustrated in a. The PEO crystal has more regular chain alignment, so PCL nucleates easier on PEO crystal surface than on oriented PEO melt surface, such as illustrated in b. 相似文献
14.
C. R. M. de Lima P. R. S. de Souza R. T. Stopilha W. A. de Morais G. T. M. Silva J. S. Nunes 《Journal of Dispersion Science and Technology》2018,39(1):83-91
Interpolyelectrolyte complex (IPEC) dispersions were prepared from chitosan and poly(sodium acrylate), NaPMA, by mixing their solutions, at different carboxyl-to-aminium molar ratios, rCA. Gyration radius was determined by small angle x-ray scattering (SAXS) and showed that, as rCA was increased, IPEC dimensions decreased and reached a minimum at rCA?=?0.75, which was considered the ratio at which IPEC cluster dimensions were minimum, following collapse, phase segregation, nucleation, and growth of larger particles. Pair distance distributions, P(r), became narrower up to rCA?=?0.75, increasing its width from this point. Relaxation-related parameters from dynamic light scattering (DLS) intensity correlation functions (ICFs) identified three main relaxation processes. The fast process, related to free polyelectrolyte molecules random motion disappeared as rCA, was increased. The other two relaxation processes also were a function of rCA and presented marked changes at rCA?=?0.75. At the same value of rCA, the energy of activation for the average relaxation rate showed the occurrence of a clear change in the nature of IPEC-related interactions. As hydrodynamic diameter, determined by DLS, was much larger than the gyration radius determined by SAXS, IPEC particles could be described as being composed by a core, rich in segregated, insoluble material, enveloped by IPEC soluble clusters, possibly in the form of water-rich gels. 相似文献
15.
Using UV-spectroscopy and transmittance electron microscopy it was shown that the structure of macromolecules and molecular weight of poly(acrylic acid) can significantly affect the synthesis and stabilization of so-called “blue silver.” 相似文献
16.
Kyu-Oh Kim Yun-A Seo Byoung-Suhk Kim Kee-Jong Yoon Myung-Seob Khil Hak-Yong Kim Ick-Soo Kim 《Colloid and polymer science》2011,289(8):863-870
We report solution properties of the blend solutions of poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG)–POSS telechelic
and its corresponding hybrid nanofibers prepared by electrospinning. The morphologies, microstructures, and wettability of
the resulting PVA/PEG3.4k–POSS hybrid nanofibers are studied. The morphologies of the resultant PVA/PEG3.4k–POSS nanofibers
are regular with the fiber diameter ranging from 610 ± 110 to 810 ± 280 nm. When the content of PEG3.4k–POSS telechelic increases
above 20 wt.%, the beaded fiber morphologies are observed due to severe aggregations of the PEG3.4k–POSS telechelics as well
as increased viscosity at higher concentration. In addition, the solution properties of pure PEG3.4k–POSS telechelic solution
(ca. 3–5 wt.%) and PVA/PEG3.4k–POSS solutions blended with PVA are explored, and found to show the reversible turbid-to-transparent
transition behavior with respect to the solution temperature. Water contact angle measurement of the PVA/PEG3.4k–POSS nanofiber
membranes demonstrates an enhanced hydrophobic nature due to the incorporated POSS moieties. 相似文献
17.
S. Affrossman R. Jerome S. A. O'Neill T. Schmitt M. Stamm 《Colloid and polymer science》2000,278(10):993-999
Thin films of blends of polystyrene (PS) and poly(n-butyl methacrylate) (PBMA) were prepared by spin-casting onto silicon wafers in order to map the lateral distribution of
the two polymers. The surfaces were examined by atomic force microscopy (AFM) secondary ion mass spectroscopy X-ray photoelectron
spectroscopy (XPS) and photoemission electron microscopy (PEEM). Films with PBMA contents of 50% w/w or less were relatively
smooth, but further increase in the PBMA content produced, initially, protruding PS ribbons and then, for PBMA ≥80% w/w, isolated
PS islands. At all concentrations the topmost surface (0.5–1.0 nm) was covered by PBMA, whilst the PBMA concentration in the
near-surface region, measured by XPS, increased with bulk content to eventual saturation. PEEM measurements of a PS–PBMA film
at the composition at which ribbon features were observed by AFM also showed a PS-rich ribbon structure surrounded by a sea
of mainly PBMA.
Received: 6 December 1999/Accepted: 5 April 2000 相似文献
18.
《Journal of membrane science》1998,147(2):235-245
Phase-inversion membranes formed from poly(acrylonitril–co-vinylchloride) (PAN–PVC) have been utilized for encapsulating living cells for transplantation; however, a detailed analysis of the structure and function of the integral skin layer has not been reported. PAN–PVC membranes fabricated under different precipitation conditions were analyzed using microscopic techniques and several functional tests. Structural analysis with scanning atomic force microscopy (AFM) revealed the presence of nodular elements in the skin layer which changed as a function of precipitation conditions. In addition, membrane hydraulic permeabilities, sieving coefficients, and diffusive permeabilities also varied with precipitation conditions. Furthermore, changes in the functional properties could be related to the size of the nodular elements and their accompanying interstitial space. The results provide insight into the fundamental interrelationships that exist between membrane fabrication, the fine surface morphology of the skin layer, and membrane performance. 相似文献
19.
Marco Naddeo Ilaria D'Auria Gianluca Viscusi Giuliana Gorrasi Claudio Pellecchia Daniela Pappalardo 《Journal of polymer science. Part A, Polymer chemistry》2020,58(4):528-539
Linear aliphatic poly(ester)s, as thermoplastic materials, are more and more envisaged as the potential “green” alternative to traditional plastics. Aliphatic polyesters having long methylene chain behave as “polyethylene-like” materials and can be prepared by ring-opening polymerization (ROP) of macrolactones. A pyridylamidozinc(II) complex was used for the ROP of ε-caprolactone (CL) and of two large ring size lactones, the ω-6-hexadecenlactone (6HDL) and the ω-pentadecalactone (PDL). High turnover frequencies were observed for the CL polymerization, while for the macrolactones, an entropy-driven behavior was recognized. Random copolymerizations of the PDL with 6HDL and of the macrolactones with CL were successfully achieved, and the copolymer microstructure was ascertained by NMR and MALDI analyses. The copolymer melting temperatures, measured by DSC, and the thermal degradation behavior, studied by TGA in nitrogen and air atmosphere, were dependent on the copolymer's composition. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 528–539 相似文献
20.
S. M. Aldoshin L. A. Nikonova E. G. Atovmyan A. N. Utenyshev D. B. Frolov 《Russian Chemical Bulletin》1996,45(9):2148-2153
N(5-Nitrofurfurylidene)isonicotinehydrazide (1) was synthesized in the reaction of nicotinic acid hydrazide with 5-nitrofurfurol in anhydrous or aqueous ethanol. Crystals of different shape and color were obtained depending on the conditions of synthesis and the nature of the solvent. As was established by IR spectroscopy, compound1 in the crystalline state forms solvates of various types. An X-ray study of two different crystals, one obtained by recrystallization from methanol (1a), and the other obtained from aqueous acetic acid (1b), was performed. In the crystal structure of1a intermolecular hydrogen bonds (IMHB) of the NH...N(Py) type occur; the crystals1b are built of solvates with one molecule of acetic acid in which the components are bonded by the IMHB (Ac)O-H..N(Py). The solvates are linked in an infinite chain by the amidohydrate IMHB C=O...W...H-N.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2263–2268, September, 1996. 相似文献