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Terpolymerizations of newly synthesized ethylene (E), vinylcyclohexene (VCH), and 1-hexene were carried out with symmetrical metallocene catalysts

Polymer dielectric possess advantages of mechanical flexibility, low temperature processing, and cost. However, for practical applications dielectric constant of polymers is not high enough. To raise the dielectric constant, polymers are often composited with fillers of various morphologies (one-dimensional, two-dimensional, three-dimensional) and types (inorganic, organic, carbon, conductive, non-conductive). Recently discovered two-dimensional (2D) materials including graphene, transition metal dichalcogenides, MXenes, ferroelectric ceramics, etc. have been discovered. These materials have excellent electrical, mechanical, thermal properties and high specific surface area, which makes these ideal materials to reinforce the properties of polymers, especially dielectric properties. Here, in this review we summarize the latest developments regarding the use of 2D fillers to improve the dielectric properties of polymer composites. We have systematically discussed synthesis of 2D materials, processing of their 2D filler/polymer composites, theoretical background of dielectric properties of these composites, and literature summary of the dielectric properties of polymer composites with various type of 2D fillers.

The objectives of this work were to address the fundamental characteristics of ansa-zirconocene catalyzed E/diene copolymerization and E/diene/1-hexene and E/diene/propylene terpolymerizations, and the quantitative relationship between diene structure and polymer chain propagation rate constant in term of quantifiable catalytic active sites. One of the most important but unknown factors in olefins ansa-zirconocene complexes is the distribution of the catalyst between sites actively participating in polymer chain formation and dormant sites. A set of ethylene/dienes copolymerizations, and ethylene/dienes/1-hexene and ethylene/dienes/1-hexene terpolymerizations catalyzed with ansa-zirconocenes/borate/triisobutylaluminium (rac-Et(Ind)2ZrCl2/[Ph3C][B(C6F5)4]/triisobutylaluminium (TIBA) were performed in toluene at 50 °C To determine the active center [C*]/[Zr] ratio variation in the copolymerization of E with different dienes and their terpolymerization with 1-hexene and propylene, each polymer propagation chain ends were quenched with 2-thiophenecarbonyl, which selectively quenches the metal–polymer bonds through acyl chloride. The ethylene, propylene, 1-hexene, and diene composition-based propagation rate constants (kpE, kpP, kp1-H, and kpdiene), thermal (melting and crystalline) properties, composition (mol% of ethylene, propylene, 1-hexene, and diene), molecular weight, and polydispersity were also studied in this work. Systematic comparisons of the proportion of catalytically [Zr]/[C*] active sites and polymerization rate constant (kp) for ansa-zirconocenes catalyzed E/diene, E/diene/1-hexene, and E/diene/propylene polymerization have not been reported before. We evaluated the addition of 1-hexene and propylene as termonomers in the copolymerization with E/diene. To make a comparison for each diene under identical conditions, we started the polymerization by introducing an 80/20 mole ratio of E/P and 0.12 mol/L of 1-hexene in the system. The catalyst behavior against different dienes, 1-hexene, and propylene is very interesting, including changes in thermal properties, cyclization of 1-hexene, and decreased incorporation of isoprene and butadiene, changes in the diffusion barriers in the system, and its effect on kp.

It is imperative to develop new and efficient electrode materials intended for electrochemical energy storage to accomplish increasing energy demand. Ternary cobalt-nickel-sulfides have gained more attention for energy storage owing to their superior redox chemistry and higher electronic conductivity as electrode materials. Herein, distinctive flower-like CoNi2S4 nanoneedle arrays (CNS–NAs) have been efficiently synthesized on Ni-foam by a very simple hydrothermal method for superior supercapacitors (SCs) electrode performances. The formation of CNS–NAs was depended upon an anion-exchange reaction mechanism relating to the pseudo-Kirkendall effect. The morphology, structure, and physical/chemical properties of the resulting material were analyzed by SEM, TEM/HRTEM, BET, XRD, and XPS. The electrochemical performances in the three-electrode system were evaluated by CV, GCD, and EIS measurements. The as-synthesized CNS–NAs exhibited a higher specific capacitance value of 2300 F/g at a current density of 1 mA/g and excellent cyclic stability with 93.8% capacitive retention after 5000 charge-discharge cycles. Larger surface area, outstanding electrical conductivity, abundant active cites, and distinctive flower-like morphology with the outstanding structural stability of CNS–NAs could be the reasons for its significant effect on the charge transfer and storage which consequences the superior electrochemical performances. In brief, this work offers a cost-effective and facile method to synthesize a promising electrode material for the potential application of high-performance SCs.

Copolymerization of ethylene (E) with 5-vinyl-2-norbornene (VNB) catalyzed by ansa-metallocenes allows the precise control of essential polymeric properties such as comonomer incorporation, molecular weight (Mw), and polydispersity (Đ).

Herein, hollow nitrogen-doped carbon microspheres (HNCMs) have been synthesized with controlled shell thickness and high surface area by pyrolysis of polydopamine-coated polystyrene (PS@PDA) core-shell microspheres. A polystyrene (PS) core was removed from the core-shell structures by pyrolysis at 500 °C under N2 atmosphere. Charge transfers, redox transformations (caused by N–H/catechol groups of the polydopamine (PDA)), and pyrolysis (introduce the nitrogen atoms along with a high degree of graphitization) may be attributed to the increase in the electrochemical and electrocatalytic performances. Our resulting material exhibited the improved electrochemical behavior towards supercapacitors with the maximum specific capacitance of 261.6 F g−1 at a scan rate of 2 mV s−1. It also showed moderate electrocatalytic properties via a 4-electron pathway mechanism (with high onset potential of 0.919 V vs. RHE at 1600 rpm) during oxygen reduction reaction. Importantly, the synergistic effect of heat treatment and a suitable concentration of PDA enhance the electrochemical performances of HNCMs.

To design a highly efficient electrocatalyst for cathodes to suppress the high overpotential for the oxygen reduction reaction (ORR) continually remains a prime goal of fuel cell study. Herein, the production of metal–free hollow nitrogen–doped carbon microspheres (HN–CMs) as an efficient electrode material for the supercapacitors and ORR in an alkaline media is reported. Initially, the PS@PANI core–shell microspheres were produced by coating polyaniline (PANI) layers on polyvinylpyrrolidone (PVP) functionalized polystyrene (PS) microspheres via in–situ chemical polymerization of aniline monomers in presence of ammonium persulphate (APS) as an oxidant. Finally, the core was removed by carbonizing the core–shell microspheres under the N2 atmosphere at 500 °C for 2 h to obtain the HN–CMs as an electrocatalyst. The structure and morphologies of the microspheres were examined by SEM, TEM, XRD, FT–IR, BET, and Raman spectroscopy. The electrochemical analysis was performed by CV, GCD, and EIS. The obtained electrocatalyst exhibited improved electrochemical performances for supercapacitors application and demonstrated better electrocatalytic activity for ORR. For this electrocatalyst, the maximum specific capacitance of 266.7 F g−1 was obtained in 1 M KOH at scan rate of 5 mV s−1. Additionally, it has superior catalytic activity and stability via 4-electron process during ORR in the alkaline solution. The contribution of highly intact spherical/hollow structure, good surface area, and large contents of graphitic/pyridinic nitrogen of HN–CMs can improve the mass transportation by facilitating the diffusion pathways which results in the enhancement of its electrochemical and electrocatalytic properties. As a metal–free and cost–effective electrode material, this is supposed to be promising for supercapacitors and fuel cells.

Background: Dyslipidemia is one of the modifiable risk factors of coronary heart disease. Objective: To determine the pattern of dyslipidemia among rural population. Methodology: This was a cross sectional study conducted in rural area of Rahim Yar Khan as a part of large study regarding prevalence of coronary heart disease. A total of 2000 study subjects were included by systematic random sampling technique, from 22 clusters of subdistricts, Rahim Yar khan, Pakistan. Patients excluded from study were; on statin therapy, patients with hypothyroidism, diabetes mellitus. Informed verbal consent was taken form each patient. Fasting venous blood samples was taken for serum total cholesterol level, serum triglycerides level, low density lipoprotein (LDL) and high-density lipoprotein (HDL). Lipid profile was considered deranged if any one of the followings was present: Total Cholesterol level >200mg/dl, Triglyceride (TG) level >150mg/dl, High density lipoprotein (HDL) 130 mg/dl. Data was entered and analyzed using computer program SPSS version 16.0. Results: A total of 2000 study subjects were included in this study, with male 792(39.6%) and females 1208 (60.4%). Mean age of study subjects was 46±9.6 years. Overall 843 (42%) study subjects have deranged lipids, with 26 (1.3%) having high LDLc, 45 (2.2%) having high cholesterol, 375 (18.8%) having high triglycerides and 538 (27%) low HDLc. Conclusion: This study showed that there was high frequency of deranged lipids among general population of rural background. Most common component among deranged lipids were low HDLc, followed by high triglycerides, high cholesterol and high LDLc. Key Words: Dyslipidemia, Rural population, Prevalence

Nitrogen-doped hollow carbon spheres (NHCSs) derived from polystyrene@polypyrrole-polyaniline (PS@PPY-PANI) core-shell composite microspheres of large surface area with improved electrochemistry performances have been effectively prepared and characterized systematically. NHCSs exhibited exceptional electrochemical properties with a maximum specific capacitance of 294.9 F g−1 at a 5 mVs−1 with good cycling stability of 95% after 5000 cycles at 0.5 A g−1. It also showed enhanced oxygen reduction reaction (ORR) activity with a high onset potential of 0.83 V vs. RHE at 1600 rpm via the more favorable four-electron pathway in an alkaline medium. Enhanced electrochemical and electrocatalytic performances could arise from the hollow porous spherical structure, high surface area, and considerable pyrrolic-pyridinic nitrogen contents. Pyrolysis commences the incorporation of nitrogen units together with the high degree of graphitization which contributes exceptionally to improve the ion/charge transfers. Significantly, the synergistic effect of pyrolysis and the proper concentration of PPY-PANI improve the overall electrochemistry performances of NHCSs. The excellent cyclic stability, high specific capacitance, and exceptional ORR activity indicate its perspective as an efficient electrode material for supercapacitors and fuel cells.