Styrene polymerization catalyzed by metal porphyrin complex/MAO for in situ synthesizing polystyrene containing air stable pi cation radicals

A novel catalyst system based on nickel(II) tetraphenylporphyrin (Ni(II)TPP) and methylaluminoxane for styrene polymerization was developed. This catalyst system has a high thermal stability and show fairly good activity. The obtained polystyrene (PS) was isotactic-rich atactic polymer by C-13 NMR analysis, and its molecular weight distribution was rather narrow (M-w/M-n approximate to 1.6, by GPC analysis). ESR revealed that Ni(II)TPP pi cation radicals were formed in the polymerization and could remain in the resulting PS stably. The mechanism of the polymerization was discussed and a special coordination mechanism was proposed. The PS product containing Ni(II)TPP pi cation radicals can be used as a potential functional material.

Characterization of High Melt Strength Polypropylene Synthesized via Silane Grafting Initiated by In Situ Heat Induction Reaction

High melt strength polypropylene (HMSPP) was synthesized by in situ heat induction reaction, in which pure polypropylene (PP) powders without any additives were used as a basic resin and vinyl trimethoxysilane (VTMS) as a grafting and crosslinking agent. The grafting reaction of VTMS with PP was confirmed by FTIR. The structure and properties of HMSPP were characterized by means of various measurements. The content of grafted silane played a key role on the melt strength and melt flow rate (MFR) of HMSPP. With increasing the content of grafted silane, the melt strength of HMSPP increased, and the MFR reduced. In addition, due to the existence of cross-linking structure, the thermal stability and tensile strength of HMSPP were improved compared with PP.

Micelle-assisted synthesis of polyaniline/magnetite nanorods by in situ self-assembly process

Polyaniline/magnetite nanocomposites consisting of polyaniline (PANI) nanorods surrounded by magnetite nanoparticles were prepared via an in situ self-assembly process in the presence of PANI nanorods. The synthesis is based on the well-known chemical oxidative polymerization of aniline in an acidic environment, with ammonium persulfate (APS) as the oxidant. An organic acid (dodecylbenzenesulfonic acid, DBSA) was used to replace the conventional strong acidic (1 M HCl) environment. Here, dodecylbenzenesulfonic acid is used not only as dopant, but also as surfactant in our reaction system.

Effects of thermal annealing on polymer photovoltaic cells with buffer layers and in situ formation of interfacial layer for enhancing power conversion efficiency

We have investigated the effects of thermal annealing before and after cathode deposition on poly(3-hexylthiophene)(P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend photovoltaic cells with different cathode buffer layers. The introduction of cathode buffer layer such as lithium fluoride (LiF) and calcium oxide (CaO) in pre-annealing cells can increase the open-circuit voltage (V-oc) and the power conversion efficiency (PCE). Post thermal annealing after cathode deposition further enhanced the PCE of the cells with LiF/Al cathode.

In Situ Scanning Tunneling Microscopy on the Dynamic Process of the Replacement of Coronene on Au (111) by 6-Mercapto-1-Hexanol

The replacement of coronene monolayer on Au (111) by 6-mercapto-1-hexanol (MHO) was studied by in situ scanning tunneling microscopy (STM) in solutions. It was found that the rate of replacement depends strongly on the concentration of MHO. The replacement finished within a second at a higher concentration of MHO. At a lower concentration, the slow replacement could be followed by in situ STM. The replacement occurred initially near the elbow position of reconstructed Au (111) with the formation of pits in a single or several missing molecules. With the proceeding of replacement, these small pits expanded, and the surrounding coronene molecules were gradually substituted by MHO, which developed into ordered domains within a spatial confined environment. Meanwhile, the reconstruction of Au (111) was lifted. The replacement expanded fast along the reconstruction lines in the domain. For the fast replacement, a (root 3 x root 3) R30 degrees adlattice was observed, while a c(4 x 2) superlattice was observed for the slow replacement.

Phase Behavior and dewetting for polymer blend films studied by in situ AFM and XPS: From thin to ultrathin films

In this work, the film thickness (l(0)) effect on the phase and dewetting behaviors of the blend film of poly(methyl methacrylate)/poly (styrene-ran-acrylonitrile) (PMMA/SAN) has been studied by in situ atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The thinner film shows the more compatibility of the blend, and the phase separation of the film occurs at l(0) > 5R(g) (radius of gyration). An initially time-independent q*, the characteristic wavenumber of the phase image, which is in good agreement of Cahn's linearized theory for the early stage of spinodal decomposition, has been obtained in real space and discussed in detail. For 5R(g) > l(0) > 3R(g), a "pseudo-dewetting/(phase separation + wetting)" behavior occurs, where the pseudo-wetting is driven by the concentration fluctuation mechanism. For 10 < 3R(g), a "real dewetting/(phase separation + wetting)" behavior occurs.

Preparation of DNA - Silver nanohybrids in multilayer nanoreactors by in situ electrochemical reduction, characterization, and application

Novel nanocomposite films containing DNA-silver nanohybrids have been successfully fabricated by combined use of the layer-by-layer self-assembly technique and an in situ electrochemical reduction method with the DNA-Ag+ complex as one of the building blocks. UV-vis absorption spectroscopy was employed to monitor the buildup of the multilayer films, which suggested a progressive deposition with almost an equal amount of the DNA-Ag+ complex in each cycle. The following electrochemical reduction of silver resulted in the formation of metal nanoparticles in the film, which was evidenced by the evolution of the intense plasmon absorption band originating from silver. Scanning electron microscopy indicated that the particles formed in the multilayer films possessed good monodispersity and stability, thanks to the surrounding polymers. X-ray photoelectron spectroscopy further confirmed the presence of the main components (such as DNA and metallic silver) of the nanocomposite films. In addition, we show that the size of the metal nanoparticles and the optical property of the film could be readily tuned by manipulating the assembly conditions.

Uniaxial deformation of overstretched polyethylene: In-situ synchrotron small angle X-ray scattering study

Synchrotron small angle X-ray scattering was used to study the deformation mechanism of high-density polyethylene that was stretched beyond the natural draw ratio. New insight into the cooperative deformational behavior being mediated via slippage of micro-fibrils was gained. The scattering data confirm on the one hand the model proposed by Peterlin on the static structure of oriented polyethylene being composed of oriented fibrils, which are built by bundles of micro-fibrils. On the other hand it was found that deformation is mediated by the slippage of the micro-fibrils and not the slippage of the fibrils. In the micro-fibrils, the polymer chains are highly oriented both in the crystalline and in the amorphous regions. When stretching beyond the natural draw ratio mainly slippage of micro-fibrils past each other takes place. The thickness of the interlamellar amorphous layers increases only slightly. The coupling force between micro-fibrils increases during stretching due to inter-microfibrillar polymer segments being stretched taut thus increasingly impeding further sliding of the micro-fibrils leading finally to slippage of the fibrils.

Structural characterization and property of in-situ synthesized AZ91-Mg2Si composite

A new-type Mg2Si composite was prepared with Mg-9Al-1Zn (AZ91) alloy and vermiculite as raw materials by melt infiltration method. The results show that the microstructure of composite consists of a large amount Of Mg2Si precipitates and a little amount of MgO embedded in alpha-Mg matrix. The Vickers hardness of the composite is obviously higher than that of matrix of AZ91 alloy. Moreover, the composite exhibits excellent compressive property. The ultimate compressive strength of the material is 290 MPa, the yield strength is 175 MPa, and the elongation is about 5%, which are higher than those of AZ91 alloy.

Facile synthesis and characterization of hyperbranched poly(ether amide)s generated from Michael addition polymerization of in situ created AB(2) monomers

A new straightforward strategy for synthesis of novel hyperbranched poly (ether amide)s from readily available monomers has been developed. By optimizing the reaction conditions, the AB(2)-type monomers were formed dominantly during the initial reaction stage. Without any purification, the AB(2) intermediate was subjected to further polymerization in the presence (or absence) of an initiator, to prepare the hyperbranched polymer-bearing multihydroxyl end-groups. The influence of monomer, initiator, and solvent on polymerization and the molecular weight (MW) of the resultant polymers was studied thoroughly. The MALDI-TOF MS of the polymers indicated that the polymerization proceeded in the proposed way. Analyses of H-1 NMR and C-13 NMR spectra revealed the branched structures of the polymers obtained. These polymers exhibit high-moderate MWs and broad MW distributions determined by gel permeation chromatography (GPC) in combination with triple detectors, including refractive index, light scattering, and viscosity detectors. In addition, the examination of the solution behavior of these polymers showed that the values of intrinsic viscosity [eta] and the Mark-Houwink exponent a were remarkably lower compared with their linear analogs, because of their branched nature.

In-situ fabrication of hybrid polyoxometalate nanoparticles composite films

inorganic-organic hybrid nanoparticles multilayer films were fabricated by extending the method of nucleation and growth of particles in polymer assemblies. The polyelectrolyte matrix was constructed by layer-by-layer self-assembly method. Synthesis of polyoxometalate nanoparticles was achieved by alternately dipping the precursor polyelectrolyte matrix into AgNO3 and H4SiW12O40 aqueous solutions. Repeating the above synthesis process, Ag4SiW12O40 nanoparticles with controllable diameters of 20 to 77 nm were synthesized in the multilayer films in-situ. UV-vis absorption spectra indicate that the nanoparticles grew gradually in the synthesis process. Transmission electron microscopy was used to observe the size and morphology of the nanoparticles.