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1.
Dunshen Zhu Xingxian Shou Yixin Liu Erqiang Chen Stephen Zhengdi Cheng 《Frontiers of Chemistry in China》2007,2(2):174-177
The AFM-tip-induced crystallization of poly(ethylene oxide) (PEO) melt droplets was studied. The melt droplets with a height
of 50–100 nm and a lateral size of 2–3 μm were obtained by melting the PEO ultra-thin films on a mica surface. For the PEO
samples with average molecular weights (M
n) ranging from 1.0 × 103 g/mol to 1.0 × 104 g/mol, the lateral perturbation from the AFM tip in the hard-tapping or nanoscratch modes could not induce the growth of
the flat-on lamellae. In contrast, under AFM nanoindentation mode, the tip-induced crystallization occurred when a sufficiently
high vertical tip force was applied to the melt droplets of PEO with M
n ⩾ 1.0 × 104 g/mol. Moreover, the experimental results indicated that the AFM-tip-induced crystallization of PEO in the nanoindentation
process had molecular weight dependence.
Translated from Acta Polymerica Sinica, 2006, (4): 553–556 (in Chinese) 相似文献
2.
By means of differential scanning calorimetry, the phase diagram of the poly(ethylene oxide)–p-bromotoluene system (PEO–PBT) is established. It is found that PEO and PBT form a molecular intercalate with a molar stoichiometry
of 22%, which corresponds to two PBT molecules for seven ethylene oxide units. The intercalate undergoes an incongruent melting
at 48.5 °C on heating. Wide-angle X-ray diffraction experiments indicate that the PEO–PBT intercalate has a crystalline structure
different from pure PEO. From variable-temperature Fourier transform IR spectroscopy investigations, it is believed that the
macromolecular chains in the PEO–PBT intercalate adopt a 7/2 helical conformation which is identical to that in the pure PEO.
There are a considerably large number of helical structures in the melt of the PEO–PBT intercalate at temperatures ranging
from 50 to 60 °C even though the crystalline lattices collapsed in the aforementioned temperature range. Such a kind of melt
is in a conformationally high order state.
Received: 5 March 2001 Accepted: 31 August 2001 相似文献
3.
C. Vanderdonckt M. Krumova F. J. Baltá Calleja H. G. Zachmann S. Fakirov 《Colloid and polymer science》1998,276(2):138-143
Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h)
in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000).
Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times
give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H
PET
c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that
the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase
of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity,
crystal thickness) which is formed at given heat treatment conditions.
Received: 29 April 1997 Accepted: 23 September 1997 相似文献
4.
Synthesis of large-pore SBA-15 silica using poly(ethylene oxide)-poly(methyl acrylate) diblock copolymers 总被引:1,自引:0,他引:1
Liang Cao Hongchen Dong Liang Huang Krzysztof Matyjaszewski Michal Kruk 《Adsorption》2009,15(2):156-166
Poly(ethylene oxide)-poly(methyl acrylate) diblock copolymers with narrow molecular weight distributions were synthesized
using atom transfer radical polymerization. The copolymers were used as micellar templates for the synthesis of mesoporous
silicas. The products were characterized using small-angle X-ray scattering, transmission electron microscopy (TEM) and nitrogen
adsorption. The obtained silicas exhibited two-dimensional hexagonal structures of cylindrical mesopores, and thus can be
classified as SBA-15 silicas. In some cases, the size of ordered domains was very small. The (100) interplanar spacings were
13–17 nm, depending on the size of the diblock copolymer used and on the synthesis conditions. Nitrogen adsorption showed
that the silicas exhibited specific surface areas of 350–800 m2 g−1, pore volumes ∼1 cm3 g−1, and narrow pore size distributions. The BJH (nominal) pore diameters were up to ∼20 nm, but actual diameters of cylindrical
pores are expected to be somewhat smaller. In many cases, the mesopores exhibited constrictions. 相似文献
5.
Xiaoju Peng Anna Maria Hofmann Sascha Reuter Holger Frey J?rg Kressler 《Colloid and polymer science》2012,290(7):579-588
Interactions of the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) with the amphiphilic diblock copolymer Ch-lPEG30-b-hbPG24 (ChP) are studied at the air–water interface by surface pressure–mean molecular area (π–mmA) measurements of mixed Langmuir films and adsorption measurements of ChP to the air–water interface covered with DPPC monolayers
at different initial surface pressure values π
0. ChP is composed of a single hydrophobic cholesteryl (Ch) moiety covalently bound to a diblock copolymer consisting of a
hydrophilic linear poly(ethylene glycol) (lPEG) block and a hydrophilic hyperbranched poly(glycerol) (hbPG) block. Langmuir isotherms and compression moduli of the mixed Langmuir films of different molar ratios reveal distinct
interactions between DPPC and ChP during compression. It is demonstrated that the behavior of the DPPC/ChP mixtures is dominated
by DPPC up to a molar ratio of 10:1, whereas the behavior is predominantly governed by ChP in mixtures with lower DPPC content
(molar ratios of 5:1, 2:1, and 1:1). In adsorption measurements, a strong affinity of ChP to DPPC is observed after injection
into the water subphase. The surface pressure value π
in up to which ChP is able to penetrate into DPPC monolayers is determined to the remarkably high value of 48.2 mN/m which attests
the favorable interactions between DPPC and the Ch moiety of ChP. Atomic force microscopy on LB films of DPPC/ChP mixtures
of different molar ratios transferred onto hydrophilic substrates confirms the presence of two different phases, a DPPC-rich
phase and a ChP-rich phase. 相似文献
6.
Byeongmoon Jeong Doo Sung Lee Jeong‐In Shon You Han Bae Sung Wan Kim 《Journal of polymer science. Part A, Polymer chemistry》1999,37(6):751-760
The gel to sol transition of aqueous solutions of di‐ and triblock copolymers consisting of poly(ethylene oxide) and biodegradable polyesters was studied as a function of temperature. The molecular weight and the chemical composition of the biodegradable blocks, (poly(l ‐lactic acid), poly(dl ‐lactic acid), poly(dl ‐lactic acid‐co‐caprolactone), and poly(dl ‐lactic acid‐co‐glycolic acid)) were varied to investigate the effects of chain packing and relative hydrophobicity on the gel to sol transition. The block copolymers studied formed micelles at lower concentrations in water, while the concentrated solutions experienced a gel to sol transition as the temperature increased. Further increase in temperature resulted in the precipitation of polymers. With increasing molecular weight and chain packing tendency of hydrophobic biodegradable block, the gel to sol transition occurred at lower concentrations and the transition temperature ranged from 0°C to over 90°C in a relatively narrow concentration range. The results obtained in this study confirm the relationship between gelation properties and polymer structure, as well as provide more information for these polymers in drug delivery applications. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 751–760, 1999 相似文献
7.
Biodegradable multiblock copolymers were synthesized by a polycondensation of poly(ɛ-caprolactone) (PCL) diols of molecular
weight (MW)=3,000 and poly(ethylene glycol)s (PEG) of MW=3,000 with 4,4′-(adipoyldioxy)dicinnamic acid (CAC) dichloride as
a chain extender in diphenyl ether at 180 °C for 2 h, and were characterized by GPC, 1H-NMR, FTIR, UV, DSC, and WAXS. These photosensitive copolymers were irradiated by a 400-W high-pressure mercury lamp (λ>280 nm)
from 5–60 min to form a network structure. The gel contents increased with irradiation time, and attained ca. 90% after 60 min
for all copolymers. The degree of swelling in a distilled water at ambient temperature, and the rate of degradation in a phosphate
buffer solution (pH 7.2) at 37 °C increased with increasing PEG components. The shape-memory tests were performed by a cyclic
thermomechanical experiments for the photocured CAC/PCL/PEG (75/25) films. The film with a gel content of 57% showed the best
shape-memory property with strain fixity rate of 100% and strain recovery rate of 88%. 相似文献
8.
A series of triblock copolymers consisting of oligomeric segments of poly(ethylene oxide)(PEO) and poly(dimethylsiloxane) (PDMS) were synthesized. These amphiphilic polymers have the general structure (PEO)n-Z-(PDMS)m-Z-(PEO)n or inversely (PDMS)m-Z–(PEO)n-Z-(PDMS)m where “Z” is the group linking the chains of different polarity. n and m varied in the range m, n < 77. These polymers spontaneously form lyotropic mesphases if mixed with water. The phasediagrams and symmetry of the phases were determined. Moreover, photoreactive groups were attached at exactly and only the positions “Z” of the block copolymers. When photocrosslinking was induced in a particular lyotropic mesophase, the arrangement of the molecules in this phase structure was fixed. Although the phase structure collapsed when the systems were freed from water, the structure returned on reswelling. Some rules concerning the tendency of such molecules to self-organize as a function of the molecular structures are obtained. 相似文献
9.
M. Dosire 《Macromolecular Symposia》1997,114(1):51-62
The phase diagrams of some binary systems such as poly(ethy lene oxide)-p-dihalogenobenzene, poly(ethylene oxide)-resorcinol and poly(ethylene oxide)-p-nitrophenol show the existence of molecular complexes with a well definite stoichiometry. The crystal structure of these molecular complexes has been determined by wide-angle X-ray diffraction. The morphology of these molecular complexes crystallized from the melt is investigated by differential scanning calorimetry and small angle X-ray scattering. PEO-p-dichlorobenzene and PEO-resorcinol complexes crystallize from the melt as extended chains (EC) or integral folded chain (IFC) lamellar crystals. As observed for PEO oligomers, the fraction of EC crystals of PEO-resorcinol increases with the crystallization temperature. However EC crystals are present in a larger range of crystallization temperatures than for pure PEO. On the other hand, the PEO-p-nitrophenol complex crystallizes over all the studied crystallization temperature range as stable non integral folded chain (NIFC) crystals. Explanations related to the crystal structure of these complexes and to their mode of growth are invoked to explain these two deeply different lamellar morphologies. 相似文献
10.
Starch or pullulan was hydrolyzed using glucoamylase or pullulanase immobilized on N-isopropylacrylamide gel. The gel used is temperature sensitive; its mesh size becomes smaller at higher temperatures (30 °C)
and larger at lower temperatures (20 °C). The molecular weight distribution of starch is wide and it consists of high-molecular-weight
amylopectin, amylose and glucose. From the change in the chromatograms for the substrate and products, it was found that the
hydrolysis rate at 30 °C was faster than that at 20 °C for amylose, though it was the reverse for amylopectin. This finding
suggests that the smaller molecular sized amylose can enter the gel phase at both temperature, while the larger molecular
sized amylopectin can hardly do so; only the end group, which can partly enter the gel phase at 20 °C (larger mesh size),
was hydrolyzed. Further, several molecular weight pullulans (monodisperse) were hydrolyzed and the experimental chromatograms
for substrate and products confirm the hydrolysis mechanism estimated.
Received: 14 July 1998 Accepted in revised form: 26 August 1998 相似文献
11.
I. G. Rozdina N. N. Filatova A. V. Gorshkov V. V. Evreinov 《Polymer Science Series A》2013,55(1):61-64
Functionality-type distributions of macromomoners with poly(ethylene oxide) and poly(propylene oxide) chains are studied by chromatography under critical conditions. It is shown that, in the critical separation mode, separation of macromolecules with respect to size disappears and only information on the functionality-type distributions of the test samples may be derived. The critical conditions are determined experimentally with a normal phase (unmodified silica gel) for poly(propylene oxide) and with a reversed phase C18 for poly(ethylene oxide). The experimental retention volumes for bifunctional macromolecules are in satisfactory agreement with the values calculated under approximation of the Gaussian chain model. 相似文献
12.
The fluorescence mode confocal laser scanning microscopy (CLSM) is introduced as an alternative method to investigate the
bulk structure of poly(vinyl alcohol) (PVA) hydrogel. Investigations of the bulk structure of hydrogel samples, prepared by
freezing and controlled thawing of aqueous PVA solutions followed by fluorochrome conjugation, were possible in the native
state because with this technique water does not need to be removed prior to examination. This is of advantage to other methods,
such as scanning electron microscopy, requiring dehydration by critical-point drying or freeze-etching, because both may result
in a significant alteration of the gel structure. CLSM images of the hydrogel bulk structure were taken at several successive
intervals from the surface into the hydrogel (up to 60 μm) without freeze-fracturing or cutting the sample. Detailed morphological
characterization is achievable by superimposing series of images taken at successive intervals and by magnifying special regions
of interest. Images of hydrogel bulk structures revealed a continuous, three-dimensional network that originates from phase-separation
(spinodal decomposition) during the freezing period. The pore or mesh size in the cryogel increased, from about 2–7 μm, with
decreasing PVA concentration. The surface layer was only a few microns thick, and the bulk structure underneath showed neither
porosity gradients nor structural orientations.
Received: 29 April 2000/Accepted: 18 August 2000 相似文献
13.
S. Makhija E. M. Pearce T. K. Kwei 《Journal of polymer science. Part A, Polymer chemistry》1992,30(13):2693-2698
Thermal oxidation of poly(ethylene oxide) (PEO) and its blends with poly(methyl methacrylate) (PMMA) were studied using oxygen uptake measurements. The rates of oxidation and maximum oxygen uptake contents were reduced as the content of PMMA was increased in the blends. The results were indicative of a stabilizing effect by PMMA on the oxidation of PEO. The oxidation reaction at 140°C was stopped at various stages and PMMA was separated from PEO and its molecular weights were measured by gel permeation chromatography (GPC). The decrease in the number-average molecular weight of PMMA was larger as the content of PEO increased in the blends. The visual appearance of the films suggested that phase separation did not occur after thermal oxidation. The activation energy for the rates of oxidation in the blends was slightly increased compared to pure PEO. © 1992 John Wiley & Sons, Inc. 相似文献
14.
N. M. Permyakova T. B. Zheltonozhskaya V. V. Shilov N. E. Zagdanskaya L. R. Kunitskaya V. G. Syromyatnikov L. S. Kostenko 《Theoretical and Experimental Chemistry》2005,41(6):382-388
Temperature transitions have been studied in the structure of triblock copolymers based on poly(ethylene oxide) and poly(acrylamide)
(PAA-b-PEO-b-PAA) with central blocks of varying length and compared with individual polymers and polymer mixtures with analogous
composition. It has been established that interaction of the polymer components on account of the formation of systems of
intramolecular hydrogen bonds is strengthened by the presence of covalent bonds between the components.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 41, No. 6, pp. 364–370, November–December, 2005. 相似文献
15.
Magerramov A. M. Ramazanov M. A. Mustafaeva A. Kh. 《Russian Journal of Applied Chemistry》2010,83(7):1324-1327
The structure and properties of nanocomposites based on zinc sulfide and poly(vinylidene fluoride) were studied. The nanocomposite
material was prepared by the matrix isolation technique: ZnS nanoparticles are formed by chemical reactions in a poly(vinylidene
fluoride) powder of particle size 0.5–1.0 μm. 相似文献
16.
Reka Melinda Molnar Magdolna Bodnar John F. Hartmann Janos Borbely 《Colloid and polymer science》2009,287(6):739-744
The present investigation describes the synthesis and characterization of nanoparticles based on poly(acrylic acid) (PAA)
intramolecularly cross-linked with diamine, 2,2′-(ethylenedioxy)bis(ethylamine), using water-soluble carbodiimide. The aqueous
colloid dispersions of nanoparticles were clear or mildly opalescent depending on the ratio of cross-linking, pH of the solution,
and the molecular weight of PAA, finding consistent with values of transmittance between 3% and 99%. The structure was determined
by nuclear magnetic resonance spectroscopy, and the particle size was identified by dynamic light scattering (DLS) and transmission
electron microscopy (TEM) measurements. It was found that particle size depends on the pH, and at a given pH, it was caused
by the ratio of cross-linking and the molecular weight of PAA. Particle size measured by TEM varied in the range of 20 and
80 nm. In the swollen state, the average size of the particles measured by DLS was in the range of 35–160 nm. 相似文献
17.
Soo‐Hong Lee Soo Hyun Kim Yang‐Kyoo Han Young Ha Kim 《Journal of polymer science. Part A, Polymer chemistry》2002,40(15):2545-2555
Poly(ethylene oxide/polylactide/poly(ethylene oxide) (PEO/PL/PEO) triblock copolymers, in which each block is connected by an ester bond, were synthesized by a coupling reaction between PL and PEO. Hydroxyl‐terminated PLs with various molecular weights were synthesized and used as hard segments. Hydroxyl‐terminated PEOs were converted to the corresponding acid halides via their acid group and used as a soft segment. Triblock copolymers were identified by Fourier transform infrared spectroscopy, 1H NMR, and gel permeation chromatography. Differential scanning calorimetry (DSC) and X‐ray diffractometry of PEO/PL/PEO triblock copolymers suggested that PL and PEO blocks were phase‐separated and that the crystallization behavior of the PL block was markedly affected by the presence of the PEO block. PEO/PL/PEO triblock copolymers with PEO 0.75k had two exothermic peaks (by DSC), and both peaks were related to the crystallization of PL. According to thermogravimetric analysis, PEO/PL/PEO triblock copolymer showed a higher thermal stability than PL or PEO. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2545–2555, 2002 相似文献
18.
Polymer electrolyte systems were prepared for the first time by dissolution of amidomagnesium chlorides in poly(ethylene oxide),
(PEO). For the preparation, solutions of (hexamethyldisilylamido)magnesium chloride, (dimethylpyrrolyl)magnesium chloride,
(diisopropylamido)magnesium chloride, piperidinomagnesium chloride and morpholinomagnesium chloride were chosen. The composition
of these polymer electrolyte systems corresponds to the general formula R2NMgCl·P(EO)n·THF. Most work has been done with the system (hexamethyldisilylamido)magnesium chloride in PEO, (Me3Si)2NMgCl·P(EO)n·THF, with n= 3, 4, 5, or 7. The electrolytes have a soft rubber-like consistency. At 30 °C, electrical conductivities of 10−6–10−5 S/cm were found. The conductivities were measured in the temperature range 20–60 °C. Within this temperature range a linear
dependence of the logarithms of the conductivity on the inverse temperature was found and activation energies for the conducting
process of 30–60 kJ/mol were calculated. Using those polymer electrolytes with a high content of the amidomagnesium compound,
a reversible magnesium deposition takes place by cathodic reduction at potentials below −1.9 V vs. a Ag/AgCl reference electrode.
These polymer electrolytes were found to be stable against oxidation up to about −0.3 V vs. Ag/AgCl.
Electronic Publication 相似文献
19.
Series of PTT-b-PEO copolymers with different composition of rigid PTT and PEO flexible segments were synthesized from dimethyl terephthalate (DMT), 1,3-propanediol (PDO), poly(ethylene glycol) (PEG, Mn = 1000 g/mol) in a two stage process involving transesterification and polycondensation in the melt. The weight fraction of flexible segments was varied between 20 and 70 wt%. The molecular structure of synthesized copolymers was confirmed by 1H NMR and 13C NMR spectroscopy. The superstructure of these polymers was characterized by DSC, DMTA, WAXS and SAXS measurements. It was observed that domains of three types can exist in PTT-b-PEOT copolymers: semi-crystalline PTT, amorphous PEO rich phase (amorphous PEO/PTT blended phase) and semi-crystalline PEO phase. Semi-crystalline PEO phase was observed only at temperature below 0 °C for sample containing the highest concentration of PEO segment. The phase structure, thermal and mechanical properties are effected by copolymer composition. The copolymers containing 30÷70 wt% of PEO segment posses good thermoplastic elastomers properties with high thermal stability. Hardness and tensile strength rise with increase of PTT content in copolymers. 相似文献
20.
Visit Vao-Soongnern 《Polymer Science Series A》2014,56(6):928-935
An overview of the recent development of a multiscale simulation of amorphous polymeric materials at the bulk density is presented. Poly(ethylene oxide), (PEO), (CH3O-[CH2-CH2-O]nCH3) was selected to illustrate the method. The model starts from an ab initio quantum chemistry to obtain the statistical weights of polymer conformation based on the rotational isomeric state (RIS) theory. PEO chains were then mapped to a coarse-grained model using the modified RIS model onto the second nearest neighbor diamond (2nnd) lattice. The average non-bonded interactions were treated by the discretized Lennard-Jones (LJ) potential. Bulk PEO melts with molecular weight up to 8000 g/mol was generated and equilibrated. The on-lattice properties such as molecular size and conformational statistics agree well with the theory. Fully atomistic amorphous PEO models can be obtained by the reverse-mapping procedure to recover the missing atoms. After an energy minimization step, properties including torsional angle distribution, solubility parameter and static neutron scattering structure factor are in good agreement with experimental results. 相似文献