The self-assembly of amphiphilic block copolymers has received much attention in recent years due to their potential applications.[1]Various morphologies,include micelles,vesicles,wormlike,bowls andporous spheres can ...
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The self-assembly of amphiphilic block copolymers has received much attention in recent years due to their potential applications.[1]Various morphologies,include micelles,vesicles,wormlike,bowls andporous spheres can be obtained by properly tuning either the polymer composition or assembling parameters.[2]Recently,nanocomposites based on the metallic nanoparticles and polymer assemblies have
Two different monoethers, CH3CH2CH2CH 2OCH3 (NBME) and (CH3)2CHCH 2-OCH3 (IBME), and Ph2Si(OCH3) 2 were used as external donors in propylene polymerization using MgCl2/TiCl4/DIBP catalyst (DIBP: diisobutyl phthalate) ...
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Two different monoethers, CH3CH2CH2CH 2OCH3 (NBME) and (CH3)2CHCH 2-OCH3 (IBME), and Ph2Si(OCH3) 2 were used as external donors in propylene polymerization using MgCl2/TiCl4/DIBP catalyst (DIBP: diisobutyl phthalate) activated by triethylaluminium (TEA). The monoethers alone showed no improvement in the isotacticity index of polypropylene (PP). When one of the ethers and Ph2Si(OCH3)2 were added together in the polymerization system as composite external donors, the propylene polymerization activity and isotacticity index were increased as compared to those of the systems with only silane as external donor, though the melting temperature and melting enthalpy of PP decreased. The effects of the external donors on the active center distribution of the catalyst system are demonstrated by deconvolution analysis of the PP molecular weight distribution into multiple Flory components, and the mechanism of external donor regulation effects is discussed. All the results show that adding monoether in MgCl 2/TiCl4/DIBP-TEA/silane catalyst system can reduce the stereoregularity of the isotactic chains of the polymer while, it maintains the atactic PP fractions at a very low level.
＜正＞Introduction:Copolyesters of L-lactide with different comonomer units such as D-lactide,meso-lactide,glycolide and-caprolactone have been widely *** has been noticed that the composition andsequential distributi...
＜正＞Introduction:Copolyesters of L-lactide with different comonomer units such as D-lactide,meso-lactide,glycolide and-caprolactone have been widely *** has been noticed that the composition andsequential distribution of comonomer units influence significantly the physical properties and biodegradability of the ***,less study has been focused on the chemical heterogeneity
＜正＞Olefin molecules have been a major source of monomers for synthetic polymers. When the double bond of a vinyl monomer is opened by a catalytic species, a chain polymerization reaction is initiated and the monome...
＜正＞Olefin molecules have been a major source of monomers for synthetic polymers. When the double bond of a vinyl monomer is opened by a catalytic species, a chain polymerization reaction is initiated and the monomer units are knitted together by single bonds, which are
In the present work, the crystallinity and dimension of crystal lattice of two series of ethylene-propylene copolymers with different propylene contents, which were prepared by a fluorinated bis(phenoxyimine) Ti catal...
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In the present work, the crystallinity and dimension of crystal lattice of two series of ethylene-propylene copolymers with different propylene contents, which were prepared by a fluorinated bis(phenoxyimine) Ti catalyst (FI-EP copolymers) and a conventional Ziegler-Natta catalyst (ZN-EP copolymers), respectively, were studied. It is found that the overall propylene content and crystallization condition have more marked effects on the crystallinity of the FI-EP copolymers with a random comonomer distribution than that of the ZN-EP copolymers with a heterogeneous comonomer distribution. The dimension of a-axis of the PE crystals increases more rapidly with the overall propylene content in the FI-EP copolymers, indicating that more propylene units are included into the PE crystals, whereas the a-axis of the PE crystals remains unchanged for all the ZN- EP copolymers. Quenching of the samples leads to more propylene units getting included into the PE crystals. The effects of comonomer content and crystallization condition on crystallinity and dimension of crystal lattice of FI-EP and ZN-EP copolymers can be explained in terms of their different comonomer distributions.
A dermal equivalent having a trilayered structure was designed by combining a silver nanoparticles incorporated chitosan film with a bilayer collagen-chitosan/silicon membrane dermal equivalent(BDE).The silver nanopar...
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A dermal equivalent having a trilayered structure was designed by combining a silver nanoparticles incorporated chitosan film with a bilayer collagen-chitosan/silicon membrane dermal equivalent(BDE).The silver nanoparticles prepared at different conditions were characterized by UV-Vis and transmission electron microscopy(TEM).The macroscopic sharp and the microstructure of the trilayer dermal equivalent(TDE) were also ***,the in vitro antibacterial property of TDE was evaluated by the antibacterial...
A method for fabricating arrays of microcapsules covalently immobilized onto chemically patterned substrates was *** core-shell microparticles with poly(allylamine hydrochloride)(PAH) as the outermost layer were obtai...
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A method for fabricating arrays of microcapsules covalently immobilized onto chemically patterned substrates was *** core-shell microparticles with poly(allylamine hydrochloride)(PAH) as the outermost layer were obtained by layer-by-layer (LbL) assembly,which were further treated with glutaraldehyde to endow the particles with abundant aldehyde groups on their *** particles were then covalently coupled to the chemically patterned regions with amino groups created by microcontact printing (μCP).After dissolution of the core particles,arrays of the hollow microcapsules with unchanged structures were *** arrays could stand rigorous environmental conditions of higher ionic strength,and lower and higher pH ***,the technique could be possibly applied to exploiting chips of microcontainers or microreactors in sensing technology.
The polymerization of alkyl isocyanates catalyzed by rare earth chloride salen complexes/triisobutyl aluminum (Ln(H2salen)2Cl3·2C2H7OH/Al(i-Bu)3) at room temperature was investigated. The influences of ligand str...
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The polymerization of alkyl isocyanates catalyzed by rare earth chloride salen complexes/triisobutyl aluminum (Ln(H2salen)2Cl3·2C2H7OH/Al(i-Bu)3) at room temperature was investigated. The influences of ligand structure, catalyst composition, polymerization temperature, polymerization time, the concentration of catalyst and monomer, and the polymerization solvent on the polymerization of isocyanates were studied. It was found that under the polymerization conditions, examined La(H2salenA)2Cl3·2C2-H7OH/Al(i-Bu)3 (H2salenA= N,N′-disalicylideneethylene diamine) is a fairly high efficient catalyst for the polymerization of n-hexyl isocyanate (n-HexNCO) to prepare high molecular weight poly(n-hexyl isocyanate) (PHNCO) with narrower molecular weight distribution at room temperature. PHNCO could be prepared with yield of 74.0%, number-average molecular weight (M n) of 40.20×104 and MWD of 1.79 under the following optimum conditions: [Al]/[La] = 30 (molar ratio), [n-HexNCO]/[La] = 100 (molar ratio), [n-HexNCO] = 3.43 mol/L polymerization at 20°C for 12 h in toluene. In the same polymerization conditions, poly (n-octyl isocyanate) (PONCO) with yield of 67.3%, and poly(n-butyl isocyanate) (PBNCO) with yield of 45.5%, could be prepared respectively. The kinetics of the polymerization of n-HexNCO was also investigated and found to be first-order with respect to both monomer and catalyst concentrations.
Highly ordered honeycomb-patterned polystyrene (PS)/poly(ethylene glycol) (PEG) films were prepared by a water-assisted method using an improved setup, which facilitated the formation of films with higher regularity, ...
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Highly ordered honeycomb-patterned polystyrene (PS)/poly(ethylene glycol) (PEG) films were prepared by a water-assisted method using an improved setup, which facilitated the formation of films with higher regularity, better reproducibility, and larger area of honeycomb structures. Surface aggregation of hydrophilic PEG and adsorption of bovine serum albumin (BSA) on the honeycomb-patterned films were investigated. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were used to observe the surface morphologies of the films before and after being rinsed with water. As confirmed by the FESEM images and the AFM phase images, PEG was enriched in the pores and could be gradually removed by water. The adsorption of fluorescence-labeled BSA on the films was studied in visual form using laser scanning confocal microscopy. Results clearly demonstrated that the protein-resistant PEG was selectively enriched in the pores. This water-assisted method may be a latent tool to prepare honeycomb-patterned biofunctional surfaces.
A stable gelatin gradient providing continuous increment of signaling for cell adhesion and proliferation was fabricated within 3D poly(L-lactic acid) (PLLA) scaffolds. The porous PLLA scaffold fabricated by NaCl part...
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A stable gelatin gradient providing continuous increment of signaling for cell adhesion and proliferation was fabricated within 3D poly(L-lactic acid) (PLLA) scaffolds. The porous PLLA scaffold fabricated by NaCl particle leaching was vertically fixed on a glass vial. 1,6-Hexanediamine/propanol solution was continuously injected into the vial by a micropump to aminolyze the PLLA scaffold. As a result of reaction time difference, the introduced -NH2 groups increased continuously along with the longitude of the PLLA scaffold in the z-direction. After covalent immobilization of gelatin by glutaraldehyde coupling, the gelatin gradient scaffold was thus obtained. In vitro chondrocyte culture showed that the cells had higher viability and more extending morphology in the gelatin gradient scaffold than that in the uniform gelatin control.
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