COPOLYMERIZATION PROCESS OF TRIPHENYLMETHYL METHACRYLATE AND MMA WITH CHIRAL ANIONIC COMPLEX INITIATOR

The copolymerization process of triphenylmethyl methacrylate (TrMA) and methylmethacrylate (MMA) using chiral anionic complex initiator (-) SP-FlLi (Scheme 1) has beenstudied in toluene and THF, respectively. The copolymer obtained in toluene possessed muchhigher specific rotation than that in THF. These copolymers have shown a tendency to a random and a like alternating structure, respectively.

Dynamic constitutive model for soils considering asymmetry of skeleton curve

Based on the asymmetric characteristic of skeleton curve obtained from dynamic tests on soils,a function with double asymptotes is proposed for describing the dynamic constitutive relations of soils.The hysteresis loops observed during unloading and reloading show the same form as the skeleton curve and are constructed by taking the ultimate stress as the corresponding asymptote.The coeffcient of initial unloading modulus is used to ensure that the constructed hysteresis loop fts well with the experimental data.Then,a new dynamic constitutive model considering the asymmetry of skeleton curve is elaborated.The verifcation tests on saturated Nanjing fne sand are performed using a hollow cylinder apparatus to verify the applicability of the UD model.It is found that the predicted curves by the UD model agree well with the test data.

Sintering Temperature Dependent Magnetic and Dielectric Properties of Polycrystalline xBa_0.95Sr_0.05TiO₃-(1 - x)BiFe_0.90Gd_0.10O₃Ceramics

Polycrystalline xBa0.95Sr0.05TiO3-(1 - x)BiFe0.90Gd0.10O3 ceramics were prepared by standard solid state reaction technique using the solid solution of BaCO3, SrCO3, TiO2, Bi2O3, Fe2O3 and Gd2O3. The compound is a BiFeO3 based multiferroic material which contains both magnetic and electric properties. The synthesized ceramics noticed better properties than xBaTiO3-(1 - x)BiFeO3 because of adding rare earth element Gd which have higher magnetic moment than Fe. The prepared samples were sintered at 900˚C, 950˚C and 1000˚C for 1 h. The effect of sintering temperature on density of the compound, complex initial permeability, dielectric properties and complex impedance analysis was reported in this article. Density of the ceramics was found to be enhanced with the rise in sintering temperature which implied porosity of the compound decreased when sintering temperature was increased. Enhanced complex initial permeability was noticed for the samples up to 950˚C and this might be attributed to reducing the motion of domain wall when the ceramics were sintered above 950˚C. Value of dielectric constant increased whereas dielectric loss decreased and these modifications might be expected because of changing density and grain size due to the variation of sintering temperature. Grain resistance (resistance due to grains) was determined from complex impedance analysis and it reduced with the rise in sintering temperature. The studied multiferroic material exhibited weak ferromagnetism but is an alternative product of environmental hazard lead (Pb) based multiferroic material and it is expected to be environment friendly.

Effect of Cu Incorporation on Structure, Densification and Magnetic Properties of Polycrystalline Li_<i>x</i>Ni_0.2Zn_{0.8-2<i>x</i>}Fe_2+<i>x</i>O₄Ceramics

The polycrystalline LixNi0.2Zn0.8-2xFex+2O4 and LixNi0.1Cu0.1Zn0.8-2xFex+2O4 (x = 0.0, 0.1, 0.2, and 0.3) ferrites were synthesized by the standard solid-state reaction method. The compound was sintered at 1150˚C for 5 hours. The effect of Cu substitution and its impact on the crystal structure, microstructure, complex initial permeability and magnetization of the Ni-Zn ferrites were studied. The effect of Li+ incorporation on the properties mentioned above was also investigated. X-ray diffraction patterns of the samples indicated a single cubic spinel structure for both the compound. No effect of Cu addition on crystal structure was observed. The density of the ferrites was found to be enhanced because of adding Li whereas the porosity of the samples decreased with the content of Li ions. The average value of grain size increased with the addition of Li content. The samples having Cu ions formed bigger size grains. Frequency-dependent complex initial permeability, loss tangent, and relative quality factor were studied at room temperature using an Impedance analyzer in the range of 100 Hz - 120 MHz regions. In the low-frequency region, the prepared samples exhibited a high value of permeability and after a certain frequency, the permeability falls. The value of permeability enhanced with the increase in Li whereas loss tangent was found to be reduced. The relative quality factor graphs described that the compound has excellent frequency stability up to a certain frequency which is suitable to be used in inductors, resistors, capacitors, etc. Initial permeability for LixNi0.1Cu0.1Zn0.8-2xFex+2O4 ferrites was found high than LixNi0.2Zn0.8-2xFex+2O4 which might be attributed to having bigger size grains of Cu containing samples because of easy movement of domain wall in bigger size grains. The values of saturation magnetization (Ms) were calculated for both compounds from M-H hysteresis loops and it enhanced with the increase in Li content which might be related to the modification of predominant exchange interactions between the cations. The Cu-containing compound exhibited higher values of saturation magnetization. The cation distribution reflects this increment because ferromagnetic Ni2+ and paramagnetic Cu2+ ions occupied in the B-sites and the diamagnetic Zn and paramagnetic Li occupied in the A-sites;therefore, net magnetic moments increased gradually. The studied materials might be used as an alternative to Pb-based compounds and would be environment friendly.

Highly Active Pd-PEPPSI Complexes for Suzuki-Miyaura Cross-coupling of Aryl Chlorides:an Investigation on the Effect of Electronic Properties

Three new Pd-pyridine enlianced precatalyst preparation stabilization and initiation(PEPPSI)complexes with halogen groups on the N-heterocyclic carbene and pyridine were prepared.Tlieir structures have been clearly characterized by nuclear magnetic resonance spectroscopy and X-ray single-crystal di fraction.The e fleets of the electronic properties of halogen groups on the catalytic activity in the Suzuki-Miyaura cross-coupling of aryl chlo-rides were investigated.These Pd-PEPPSI complexes could catalyze the cross-coupling reaction efficiently with a low catalyst loading(0.05%,molar ratio)at room temperature and the products were obtained in high yields.