Search results for "Molar"

Synthesis and Characterization of Isotactic Poly(1-hexene)/Branched Polyethylene Multiblock Copolymer via Chain Shuttling Polymerization Technique

2018

Understanding from the underlying mechanism of chain shuttling polymerization (CSP) is limited due to scarceness of successful reports and incompetence of traditional characterization techniques to distinguish blocky structures. Here, a simple synthesis approach for production of an isotactic poly(1-hexene)/branched polyethylene multiblock copolymer from a 1-hexene monomer is presented. Resulting copolymers can be easily characterized because of their solubility in most organic solvents. This novel blocky architecture is synthesized using ansa-ethylenebis(1-η5-indenyl)zirconium dichloride and α-diimine nickel(II) bromide catalysts. While the former participates in 1,2-enchainment of monomer…

A critical approach to the toxic metal ion removal by hazelnut and almond shells

2018

The adsorption capacity of ground hazelnut (HS) and almond (AS) shells towards Pb(II) and Cd(II) has been studied at pH = 5, in NaNO3 and NaCl ionic media, in the ionic strength range 0.05-0.5 mol L-1. Kinetic and equilibrium experiments were carried out by using the Differential Pulse Anodic Stripping Voltammetry technique to check the amount of the metal ion removed by HS and AS materials. Different kinetic and equilibrium equations were used to fit experimental data and a statistical study was done to establish the suitable model for the data fitting. A speciation study of the metal ions in solution was also done in order to evaluate the influence of the ionic medium on the adsorption pr…

Analytic JV-Characteristics of Ideal Impurity PV-Cells

2017

In this article the mathematical modeling of idealized impurity photovoltaic cells is greatly simplified through the derivation of analytic JV-characteristics. The resulting expressions are also facilitating the intuitive understanding of such photovoltaic devices. The new model is used to investigate the sensitivity of impurity photovoltaic cells to the absorption band width, the impurity related absorptivity and the external radiative efficiency. It is found that impurities with narrow absorption bands or low absorptivity can greatly reduce the efficiency of the device, even if they are fully radiative and have energy levels situated at optimal positions in the band gap. It is also found …

The effect of combining laser and nanohydroxy-apatite on the surface properties of enamel with initial defects

2017

Background The aim of this study was to evaluate the effect of combining fractional CO2 LASER and nanohydroxy apatite on surface microhardness and color of enamel with initial defects. Material and Methods Two types of nano hydroxylapatite (nHAP) was prepared; Pure hydroxyapatite (nHA) and Fluoro hydroxyapatite (nFHA), Sixty extracted premolar teeth without visible caries or structural defects on enamel surface were used, immersed in 10 ml of a demineralizing solution for 2 weeks to create artificial white spot lesions, they were randomly allocated into two groups; Group 1: nHA, Group 2: nFHA, each group is then subdivided into 2 subgroups (A and B) where two different in vitroremineralizat…

Liquid/Liquid Demixing in the System n-Hexane/Narrowly Distributed Linear Polyethylene

2004

Demixing conditions were measured visually for solutions of three narrowly distributed polyethylene samples (M ranging from 6.5 to 380 kg/mol) in n-hexane up to 500 K and 150 bar. This information yields the critical line for infinite molar mass; i.e., it specifies the pT area within which one is safe from phase separation irrespective of the molar mass of the polymer and of the composition of the mixture. The experimental findings are in good qualitative agreement with the predictions of the Sanchez−Lacombe theory applied without any adjustable parameters. The influences of molar masses are, however, underestimated, and the resulting critical compositions are too small. For a more quantita…

Characterization of Chemical Composition along the Molar Mass Distribution in Polyolefin Copolymers by GPC Using a Modern Filter-Based IR Detector

2013

Summary Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is the technique routinely used at high temperature to analyze the molar mass distribution in polyolefins. The distribution of comonomer along the molar mass distribution in a copolymer is a key microstructural feature that determines the macroscopic properties of the material, and thus, its range of possible applications and performance. The direct coupling of a modern filter-based infrared (IR) detector to a high temperature GPC instrument, by means of a heated flow-through cell, is here described. The analyses are carried out by recording the continuous IR absorbance chromatograms at selected …

1983

The neutron scattering from mixtures of deuterated and undeuterated poly(ethylene oxide), (D-PEO, H-PEO), in the small angle and intermediate angle region has been measured in the melt. We found no indications of a molecular segregation. The value of molecular weight evaluated agreed with that obtained by other methods. For a sample with a molar mass of 120000 g/mol the radius of gyration 〈rw2〉1/2 was found to be 13,6 nm, which corresponds to a characteristic ratio of C = 6,9. The form factor of a single chain can be described by the Debye equation for a random coil with the same unperturbed dimensions. Our results are compared with rotational isomeric state calculations and measurements in…

High molecular arborescent polyoxyethylene with hydroxyl containing shell

2004

Abstract Arborescent polyoxyethylene of high molar mass (2×10 5  g/mol) and narrow molar mass distribution was synthesized in a three-stage process. In the first stage a triblock copolymer of ethylene oxide (central block, DP ca. 90) and 2,3-epoxypropanol-1 (short flanking blocks, DP ca. 5) was synthesized. The potassium alcoholate derived from this copolymer was used to initiate the polymerization of ethylene oxide and the subsequent addition of protected glycidol (1-etoxyethyl glycidyl ether). After deprotection the short polyglycidol blocks were used as branching units for the next generation. Repeated step by step process leads to the ‘pom-pom like’ branched polyoxyethylene macromolecul…

Cylindrical Polypeptide Brushes

2005

Cylindrical brushes with poly(L-lysine) and poly(L-glutamate) side chains were prepared by grafting through and grafting from techniques. Grafting from is shown to be more successful for the synthesis of cylindrical brushes with high molar mass main and side chains.

One-Step Anionic Copolymerization Enables Formation of Linear Ultrahigh-Molecular-Weight Block Copolymer Films Featuring Vivid Structural Colors in t…

2018

Ultrahigh-molecular-weight (UHMW) tapered block copolymers (BCPs) consisting of polyisoprene-block-poly(4-methylstyrene) featuring overall molar masses in the range of 1101–2033 kg mol–1 (Mw) are synthesized via a convenient one-step anionic copolymerization protocol. The obtained UHMW BCPs are investigated by differential scanning calorimetry, size exclusion chromatography, and 1H NMR spectroscopy. Microphase separation for the UHMW BCPs in the bulk state is investigated by transmission electron microscopy (TEM) measurements and scanning electron microscopy (SEM), revealing well-ordered lamellar and spherical domains with large domain sizes in the range of 100–200 nm. Excellent order and p…