Formation of nonextinct ring-banded textures and multistacked lamella of tetra-aniline-block-poly(L-lactide) rod-coil diblock oligomer films induced by solvent vapor treatment

The self-assembly processes of the rod-coil diblock oligomer thin film of tetra-aniline (TANI)-block-poly(L-lactide) (PLLA) with different film thicknesses induced in the coil-selective solvent of acetone vapor at room temperature were studied. The morphologies of the oligomer films were determined by the film thickness. For the thicker film (232 nm), the nonextinct concentric ring-banded textures could form. While for the thinner and appropriate film (about 6 nm), multistacked diamond-shaped appearances with the periodic thickness being about 8.5 nm(6-nm-thick extended PLLA chain and 2.5-nm-thick p-pi conjugating TANI bimolecular layer) formed. The possible formation models of those two regular morphologies were presented in detail.

Nature of the ring-banded spherulites in blends of aromatic poly(ether ketone)s

The ring-banded spherulites in liquid crystalline poly(aryl ether ketone) (LC-PAEK) and poly(aryl ether ether ketone) (PEEK) blends with a higher content (>50%) of LC-PAEK are investigated by polarizing light microscopy (PLM) and atomic force microscopy (AFM) techniques. The results indicate that the light core and rings of the ring-banded spherulites under PLM are mainly composed of an LC-PAEK phase, while the dark rings consist of coexisting phases of PEEK and a small amount of LC-PAEK. The formation of the ring-banded spherulites is attributable to structural discontinuity caused by a rhythmic radial growth.

Crystallization and ring-banded spherulite morphology of poly(ethylene oxide)-block-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior of crystalline-crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(epsilon-caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring-banded spherulite morphology or the PEO-b-PCL diblock copolymer.

Robust core-shell supramolecular assemblies based on cationic vesicles and ring-shaped {Mo-154} polyoxomolybdate nanoclusters: Template-directed synthesis and characterizations

Substantial progress has been made recently in extending the supramolecular assembly of biomimetic structures to vesicle-based sophisticated nanocomposites and mesostructures. We report herein the successful preparation of unilamellar surfactant vesicles coated with a monolayer of ring-shaped {Mo-154} polyoxometalate (POM) nanoclusters, (NH4)(28)[Mo-154 (NO)(14)O(448)Hi(4)(H2O)(70)].approximate to 350H(2)O, by coulomb attractions using preformed didodecyldimethylammonium bromide (DDAB) surfactant vesicles as templates. The resultant vesicle-templated supramolecular assemblies are robust (they do not disintegrate upon dehydration) both at room-temperature ambient and vacuum conditions, as characterized by conventional transmission electron microscopy (TEM) and atomic force microscopy (AFM). The flexibility of the complex soft assemblies was also revealed by AFM measurements. The effect of POM-vesicle coulomb attractions on the dimensions of the templating vesicles was also investigated by using dynamic light scattering (DLS).Although origins of the structure stability of the as-prepared supramolecular assemblies are not clear yet, the nanometer scale cavities and the related properties of macroions of the POM clusters may play an important role in it.

Synthesis, characterization and ring-opening polymerization of cyclic (arylene phosphonate) oligomers

A series of cyclic (arylene phosphonate) oligomers were prepared by reaction of phenylphosphonic dichloride (PPD) with various bisphenols under pseudo-high dilution conditions via interfacial polycondensation. The yield of cyclic (arylene phosphonate) oligomers is over 85% by using hexadecyltrimethylammonium bromide as phase transfer catalyst (PTC) at 0 degreesC. The structures of the cyclic oligomers were confirmed by a combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and IR analysis. These cyclic oligomers undergo facile ring-opening polymerization in the melt by using potassium 4,4'-biphenoxide as the initiator to give linear polyphosphonate. Free-radical ring-opening polymerization of cyclic(arylene phosphonate) oligomers containing sulfur linkages was also performed in the melt using 2,2'-dithiobis(benzothiazole) (DTB) as the initiator at 270degreesC and the resulting polymer had a M-w of 8 x 10(3) with a molecular weight distribution of 4. Ring-opening copolymerization of these cyclic oligomers with cyclic carbonate oligomers was also achieved. The average molecular weight of the resulting copolymer is higher than the corresponding, homopolymer and the thermal stability of the copolymer is better than the corresponding homopolymer.

Vacuum-deposited submonolayer thin films of a three-ring bent-core compound

Submonolayer thin films of a three-ring bent-core (that is, banana-shaped) compound, m-bis(4-n-octyloxystyryl)benzene (m-OSB), were prepared by the vacuum-deposition method, and their morphologies, structures, and phase behavior were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The films have island shapes ranging from compact elliptic or circular patterns at low temperatures (below 40 degreesC) to branched patterns at high temperatures (above 60 degreesC). This shape evolution is contrary to the prediction based on the traditional diffusion-limited aggregation (DLA) theory. AFM observations revealed that two different mechanisms governed the film growth, in which the compact islands were formed via a dewetting-like behavior, while the branched islands diffusion-mediated. It is suggested m-OSB forms a two-dimensional, liquid crystal at the low-temperature substrate that is responsible for the unusual formation of compact islands. All of the monolayer islands are unstable and apt to transform to slender bilayer crystals at room temperature. This phase transition results from the peculiar molecular shape and packing of the bent-core molecules and is interpreted as escaping from macroscopic net polarization by the formation of an antiferroelectric alignment.

Fabrication of silver nanoparticles ring templated by plasmid DNA

Silver nanoparticles ring was successfully fabricated by electrostatic assembling 4-aminothiophenol (4-ATP) capped silver nanoparticles on predefined extended circular plasmid pBR322 DNA. The silver nanoparticles ring which was about 1.5 mu m in length, and about 2.2 nm in height can be obtained by adjusting the reaction time. The normal Raman scattering spectra reveal that the 4-ATP has contacted with the silver nanoparticles by forming a strong Ag-S bond. The AFM data show that the assembly of 4-ATP capped silver nanoparticles on DNA is ordered.

Ring-opening polymerization and block copolymerization of L-lactide with divalent samarocene complex

Divalent samarocene complex [(C5H9C5H4)(2)Sm(tetrahydrofuran)(2)] was prepared and characterized and used to catalyze the ring-opening polymerization of L-lactide (L-LA) and copolymerization of L-LA with caprolactone (CL). Several factors affecting monomer conversion and molecular weight of polymer, such as polymerization time, temperature, monomer/catalyst ratio, and solvent, were examined. The results indicated that polymerization was rapid, with monomer conversions reaching 100% within 1 h, and the conformation of L-LA was retained. The structure of the block copolymer of CL/L-LA was characterized by NMR and differential scanning calorimetry. The morphological changes during crystallization of poly(caprolactone) (PCL)-b-P(L-LA) copolymer were monitored with real-time hot-stage atomic force microscopy (AFM). The effect of temperature on the morphological change and crystallization behavior of PCL-b-P(L-LA) copolymer was demonstrated through AFM observation.

Ring-opening polymerization of epsilon-caprolactone and L-lactide using organic amino calcium catalyst

Poly (6-caprolactone) (PCL) and poly (L-lactide) (PLA) were prepared by ring-opening Polymerization catalyzed by organic amino calcium catalysts (Ca/PO and Ca/EO) which were prepared by reacting calcium ammoniate Ca(NH3)(6) with propylene oxide and ethylene oxide, respectively. The catalysts exhibited high activity and the ring-opening polymerization behaved a quasi-living characteristic. Based on the Fr-IR spectra and the calcium contents of the catalysts, and based on the H-1 NMR end-group analysis of the low molecular weight PCL prepared using catalysts Ca/PO and Ca/EO, it was proposed that the catalysts have the structure of NH2-Ca-O-CH(CH3)(2) and NH2-CaO-CH2CH3 for Ca/PO and Ca/EO, respectively. The ring-opening polymerization of CL and LA follows a coordination-insertion mechanism and the active site is the Ca-O bond.

Strontium-based initiator system for ring-opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr-PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring-opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA). The Sr-PO initiator demonstrated an effective initiating activity for the ROP of epsilon-caprolactone (epsilon-CL) and L-lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr-PO initiator. Block copolymer PCL-b-PLLA was prepared by sequential polymerization of epsilon-CL and LLA, which was demonstrated by H-1 NMR, C-13 NMR, and gel permeation chromatography. The chemical structure of Sr-PO initiator was confirmed by elemental analysis of Sr and N, H-1 NMR analysis of the end groups in epsilon-CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr-PO initiator and model monomer gamma-butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination-insertion mechanism, and cyclic esters exclusively inserted into the Sr-O bond.

Synthesis and characterization of (C5H9C9H6)(2)Yb(THF)(2)(II) (1) and [(C5H9C5H4)(2)Yb(THF)](2)O-2 (2), and ring-opening polymerization of lactones with 1

Reaction of YbI2 with two equivalents of cyclopentylindenyl lithium (C5H9C9H6Li) affords ytterbium(II) substituted indenyl complex (C5H9C9H6)(2)Yb(THF)(2) (1) which shows high activity to ring-opening polymerization (ROP) of lactones. The reaction between YbI2 and cyclopentylcyclopentadienyl sodium (C5H9C5H4Na) gives complex [(C5H9C5H4)(2)Yb(THF)](2)O-2 (2) in the presence of a trace amount of O-2, the molecular structure of which comprises two (C5H9C5H4)(2)Yb(THF) bridged by an asymmetric O-2 unit. The O-2 unit and ytterbium atoms define a plane that contains a C-i symmetry center.

Synthesis, structure and ring-opening polymerization of phenolphthalein macrocyclic polyarylates

Phenolphthalein based polyarylate macrocyclic oligomers were selectively synthesized by an interfacial polycondensation reaction of o-phthaloyl dichloride with phenolphthalein. The high selectivity benefits from the role of phenolphthalein as a color indicator, an efficient phase transfer catalyst, acid a preferred conformation of the starting materials as indicated by analyzing a single-crystal X-ray structure of an analogous macrocycle. The melt ROP of phenolphthalein polyarylate cyclic dimer was studied using nucleophilic initiators, The molecular weight of the resulting polymers builds up very rapidly at the very early stage of polymerization but decreases with time. During the ROP of cyclic dimer, analogous macrocycles with higher degree of polymerization (n greater than or equal to 3) and linear oligomers were produced by backbiting reaction especially at later stage of polymerization. Conversion of cyclic dimer is very fast at the earlier stage of polymerization and then increases slowly with time as analyzed by gel permeation chromatography. However, the total amount of cyclic oligomers in the ROP system increases with time at the later stage of polymerization because of the formation of larger macrocycles. The resulting polymers are amorphous. Glass transition temperatures (T(g)s) of these polymers are influenced by the polymerization time, type of initiator, and initiator concentration.

Synthesis and free-radical ring opening polymerization of macrocyclic aryl thioether ether ketone (sulfone) oligomers

Two kinds of novel macrocyclic aryl thioether ether oligomers were synthesized by nucleophilic condensation reaction in high yields under pseudo-high-dilution condition. A combination of H-1 NMR, GPC and MALDI-TOF MS analyses unambiguously confirmed the cyclic nature and their distributions, Macrocyclic thioether ether ketone oligomers can undergo facile melt ring opening polymerization(ROP) initiated by thiyl radical to give a high molecular weight polymer.

Novel macrocyclic aryl thioether ester oligomers: structure characterization and free-radical ring opening polymerization

Novel macrocyclic aryl thioether ester oligomers have been synthesized in high yield from phthaloyl dichloride and 4,4'-thiodiphenol under pseudo high dilution conditions. The cyclic nature was unambiguously confirmed by a combination of MALDI-TOF MS, gel permeation chromatography and NMR analyses. Single-crystal X-ray diffraction of cyclic ester dimer reveals no severe strain on the cyclic structure. The free-radical ring opening polymerization (ROP) of the macrocyclic oligomers was achieved to give high molecular weight polymers via a transthioetherification reaction. The molecular weight of the polymer resulting from ROP decreases as the conversion of cyclic oligomers increases after a polymerization period of 30 min.