Preparation and properties of siloxane liquid crystalline elastomers with a mesogenic crosslinking agent

A mesogenic crosslinking agent M-1 was synthesized to minimize the perturbations of non-mesogenic crosslinking agents in liquid crystalline elastomers. The synthesis of new side chain liquid crystalline elastomers containing the rigid mesogenic crosslinking agent M-1 and nematic monomer M-2 by a one-step hydrosilylation reaction is described. The chemical structures of the monomers and network polymers obtained were confirmed by FTIR and ¹H NMR spectroscopy. The mesomorphic properties and phase behaviour were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The influence of the crosslinking units on phase behaviour is discussed. Liquid crystalline elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transitions and a threaded texture. The experimental results demonstrated that the glass transition temperature of polymers P-1-7 increased with increasing concentration of crosslinking agent M-1; but the isotropic temperature and liquid crystalline range decreased slightly.     

Morphology,structure, and properties of in situ compatibilized linear low‐density polyethylene/polystyrene and linear low‐density polyethylene/high‐impact polystyrene blends

Blends of linear low‐density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high‐impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl₃), was adopted to initiate the Friedel–Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl₃ blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel–Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE‐g‐PS and LLDPE‐g‐HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m². Scanning electron microscopy micrographs showed that the size of the domains decreased from 4–5 to less than 1 μm, depending on the content of added AlCl₃. The crystallization behavior of the LLDPE/PS blend was investigated with differential scanning calorimetry. Fractionated crystallization phenomena were noticed because of the reduction in the size of the LLDPE droplets. The melt‐flow rate of the blending system depended on the competition of the grafting reaction of LLDPE with PS and the degradation of the blending components. The degradation of PS only happened during the alkylation reaction between LLDPE and PS. Gel permeation chromatography showed that the alkylation reaction increased the molecular weight of the blend polymer. The low molecular weight part disappeared with reactive blending. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1837–1849, 2003     

Crystallographic report: Crystal structure of a two‐dimensional coordination polymer: tetraaqua‐1,2,4,5‐benzenetetracarboxylato(pyrazine)dizinc(II) dihydrate

The structure of {[Zn₂(1,2,4,5‐btc)(pz)(H₂O)₄]·2(H₂O)}_n (1,2,4,5‐btc = 1, 2, 4, 5‐benzenetetracarboxylate, pz = pyrazine) is a two‐dimensional coordination network. The zinc(II) center is in a distorted octahedral NO₅ coordination environment that is defined by one nitrogen atom of pyrazine, three oxygen atoms of carboxyl groups from 1,2,4,5‐benzenetetracarboxylate tetraanions and two water molecules. Copyright © 2003 John Wiley & Sons, Ltd.     

Poisson半群的边界值

在空间Ｌｐ（Ｒｎ），１≤ｐ＜∞中，Ｐｏｉｓｏｎ算子半群ｅ－－△ｚ是右半平面Ｒｅｚ＞０上的解析半群．本文考虑它的边界值，证明了闭稠定算子－ｉ－△对某个α≥０生成了一个指数有界（Ｉ＋－△）－α 半群．     

Crystallographic report: Crystal structure of a homoleptic lanthanide guanidinate complex: [Ph2NC(NCy)2]3Yb·2PhCH3

The title complex, [Ph₂NC(NCy)₂]₃Yb·2PhCH₃ is a monomer with a six‐coordinate ytterbium center ligated by six nitrogen atoms of three chelating bidentate guanidinate ligands. The coordination geometry around the lanthanide ion is best described as a distorted trigonal prism. Copyright © 2005 John Wiley & Sons, Ltd.     

PERIODIC SOLUTION TO PREDATOR-PREY CHAIN SYSTEM WITH IMPULSIVE EFFECTS AND BEDDINGTON-DEANGELIS FUNCTIONAL RESPONSE

In this paper, a predator-prey chain system with impulsive effects and Beddington-DeAngelis functional response is studied. We investigate the existence of periodic solu-tion by coincidence degree theory. Sufficient conditions are obtained for the existence of periodic solution.     

GLOBAL L^p ESTIMATES FOR THE PARABOLIC EQUATION OF THE BI-HARMONIC TYPE

In this paper similarly to the second-order case, we give an elementary and straightforward proof of global Lp estimates for the initial-value parabolic problem of the bi-harmonic type. Moreover, we obtain the existence and uniqueness of the solutions in the suitable space using the potential theory, Marcinkiewicz interpolation theorem and approximation argument. Meanwhile, by the same approach we can deal with the general polyharmonic cases.     

Thermomagnetic effect in ferrofluids with weakly coupled particles

Thermomagnetic curves for water based ferrofluid with large magnetic latex particles are analyzed. The particles are found to have extremely low barrier height of thermal relaxation (≤1200 K at temperatures below 100 K) whose field dependence is deduced. Work sponsored by the National Science Council of the R.O.C. under Grant No. NSC85-2112-M-001-020.     

σ-根与σ-半单类的构造

继［１～３］分别给出σ－根及其半单类的两个特征性质，研究了对于已知环类Ｍ，含于Ｍ的最大σ－根及σ－半单类和包含Ｍ的最小σ－半单类的构造，同时得到σ－半单闭包σ－遗传的一个充分条件．