Synthesis and Characterization of in situ Polyethylene and Polypropylene Nanocomposites: Gas Phase Polymerization by Nanosilica Supported <Emphasis Type="Italic">bis</Emphasis> (Cyclopentadienyl) Zirconium (IV) Dichloride Catalyst System

In the present work, in situ polyethylene and polypropylene nanocomposites have been successfully synthesized by gas phase polymerization of ethylene and propylene in presence of surface treated nanofillers with nanosilica-supported-bis (cyclopentadienyl) zirconium (IV) dichloride as a coordination catalyst. The nanofillers used are Cloisite-20A and nanosilica, respectively. These were pre-treated with MAO (Methylaluminoxane) to inhibit their deactivating action on the catalyst because of the presence of either acidic or basic groups on their surfaces; in this way MAO acts as a co-catalyst for the polymerization reactions being discussed. Two in situ Polyethylene (PE) i.e., CFPE and SFPE (Cloisite-20A filled polyethylene and nanosilica filled polyethylene) and two in situ polypropylene (PP) i.e., CFPP and SFPP (Cloisite-20A filled polypropylene and nanosilica filled polypropylene) nanocomposites have been prepared by gas-phase polymerization. The in situ polyethylene and polypropylene nanocomposites were characterized using Fourier transform infrared Spectroscope (FTIR), Thermogravimetric analyzer (TGA), Differential Scanning Calorimeter (DSC) and Scanning electron microscope (SEM). By our approach, it has been observed that the nanofillers are completely encapsulated by a thin layer of polymer chains.     

Modelling of phenol—formaldehyde polymerization reaction

In the condensation polymerization of phenol and formaldehyde, the ortho and para positions exhibit different reactivities. In addition, along a polymer chain, internal reactive sites have lower reactivity, possibly due to shielding phenomena^1,2. A detailed kinetic model for novalac formation has been proposed accounting for all these factors. Five different kinds of reactive sites have been shown to exist on a polymer chain and the reactivity of a given reaction has been assumed to be governed completely by the reactive site involved in it. A mass balance has been written for each site and the equations have been solved numerically to examine the effect of different parameters on the course of the condensation polymerization. The model predicts polymer chains with small levels of branching, which is consistent with experimental observations.     

Angle Domain Massive MIMO-OFDMA Using a Scalar Channel Estimate

Wireless Personal Communications - Massive Multiple-Input Multiple-Output (MIMO) technology has the potential to deliver high spectral efficiencies by leveraging the ability to form narrow beams...     

Chemical Tools for Studying Phosphohistidine: Generation of Selective τ-Phosphohistidine and π-Phosphohistidine Antibodies**

Nonhydrolysable stable analogues of τ-phosphohistidine (τ-pHis) and π-pHis have been designed, aided by electrostatic surface potential calculations, and subsequently synthesized. The τ-pHis and π-pHis analogues (phosphopyrazole 8 and pyridyl amino amide 13 , respectively) were used as haptens to generate pHis polyclonal antibodies. Both τ-pHis and π-pHis conjugates in the form of BSA-glutaraldehyde-τ-pHis and BSA-glutaraldehyde-π-pHis were synthesized and characterized by ³¹P NMR spectroscopy. Commercially available τ-pHis (SC56-2) and π-pHis (SC1-1; SC50-3) monoclonal antibodies were used to show that the BSA−G-τ-pHis and BSA−G-π-pHis conjugates could be used to assess the selectivity of pHis antibodies in a competitive ELISA. Subsequently, the selectivity of the pHis antibodies generated by using phosphopyrazole 8 and pyridyl amino amide 13 as haptens was assessed by competitive ELISA against His, pSer, pThr, pTyr, τ-pHis and π-pHis. Antibodies generated by using phosphopyrazole 8 as a hapten were found to be selective for τ-pHis, and antibodies generated by using pyridyl amino amide 13 were found to be selective for π-pHis. Both τ- and π-pHis antibodies were shown to be effective in immunological experiments, including ELISA, western blot, and immunofluorescence. The τ-pHis antibody was also shown to be useful in the immunoprecipitation of proteins containing pHis.     

Simulation of molecular weight distribution and cyclic oligomer formation in the polymerization of nylon 6

The reversible polymerization of nylon 6 including ring opening, polycondensation, polyaddition, and cyclization reactions as well as the reaction with monofunctional acids was simulated for an isothermal batch reactor at 235°C. The cyclic oligomer concentrations, the molecular weight distributions, and its moments have been computed using a chain length-dependent equilibrium constant for the cyclization reaction. Even though the cyclization step does not influence the monomer conversion considerably, it does effect the molecular weight distribution and its moments.     

Emphasis on Validation in Research: A Meta-Analysis

The emphasis of validity as a publication content was investigated in dissertations and journal articles. The time of first publication, longitudinal publication profile, ratio of articles to dissertations, and time lag between dissertations and articles emphasizing validity were compared within and among various fields. A three-decade gap separated the first field adopting validity-related contents in its dissertations from the latest fields that did so. The longitudinal data suggested three groups of fields (Agricultural Sciences, Applied Sciences and Social Sciences) which showed consistent differences among groups and consistent similarities within groups in their emphasis on validity-related content. Adoption of validity-related content in dissertations always preceded adoption of validity-related content in journal articles. On average, less than 4% of journal articles included validity-related content across fields. These findings support the hypothesis that validity has been introduced and disseminated within fields following patterns predicted by diffusion of innovations theory. It is argued that this pattern is inconsistent with an efficient and interdisciplinary utilization of available knowledge. Policy recommendations are made for developing strategic communication and education programs for academicians and journal reviewers.     

Parametric sensitivity of chain polymerization reactors exhibiting the trommsdorff effect

The recently developed mathematical technique for studying the parametric sensitivity of reactors is extended to include chain polymerization systems exhibiting the gel and glass effects, as well as physical property variations. The sensitivities of the two temperature maxima with respect to various parameters are computed. It is found that, for a sample system, poly(methyl methacrylate), all the sensitivities of the gel effect induced temperature peak attain their maxima at the same conditions—this leads to a generalized temperature sensitivity constraint applicable to reactor design or operation. This sensitivity boundary is associated with high conversions and high molecular weights. The analysis shows that the dimensionless propagation activation energy, ?_p, and the dimensionless initiation activation energy, ?_d, are the two most important parameters governing the system performance. Sensitivities of the gel effect-induced number average chain length peak with respect to various parameters are also obtained. Again, all of these chain length sensitivities show maxima at the same condition, leading to the concept of a generalized chain length sensitivity criterion of constraint. Most importantly, the temperature and chain length sensitivity boundaries are virtually identical.     

Poly(4‐methyl‐1‐pentene)/clay nanocomposites: effect of organically modified layered silicates

The preparation and properties of poly(4‐methyl‐1‐pentene) (PMP)/clay nanocomposites are reported. Melt intercalation of PMP is carried out with organoclays of different cation/charge exchange capacities and modifiers to facilitate intercalation of the polymer into the silicate layers. The effect of modifiers on the structure and properties of PMP/clay nanocomposites is explored. XRD patterns confirm the intercalation of polymer in the layered silicates as evidenced by the increase in the inter‐layer spacing which is dependent on the type of modifier used. Dynamic mechanical analysis shows increments in the storage modulus over the temperature range studied for all of the three clays, but the extent depends on the type of clay modifier used. The coefficient of thermal expansion is lower for all of the nanocomposites, as compared to the pristine polymer, indicating improved dimensional stability Copyright © 2003 Society of Chemical Industry