Fire retardant systems in poly(methyl methacrylate): Interactions between metal oxide nanoparticles and phosphinates

In the course of our investigations on halogen-free fire-retardant solutions for PMMA, the influence of oxide nanoparticles (TiO₂, Al₂O₃) on the thermal stability and fire behaviour of PMMA blended with phosphinate additives (Exolit OP930 and OP1311) has been studied by thermogravimetric analysis and cone calorimetry. For each mixture, the residues obtained after combustion were examined and characterized by SEM, X-ray diffraction and X-ray microprobe analysis. Some synergistic effects were obtained between nanometric alumina and OP930 additive leading to the reduction of peak of heat released rate and of total heat released up to 30% and to the increase of time to ignition. From the results obtained, it can be proposed that OP930 and OP1311 act principally in the condensed phase, the presence of oxides playing a reinforcement role in the carbonaceous layer promoted by the phosphinate additives.     

Redox potential of iron–sulfur clusters as a model of the Desulfovibrio vulgaris center

A theoretical study of Heisenberg exchange and double exchange effects in clusters with four and six iron ions has been performed for [Fe₄ S₃ O] ^m+, [Fe₄ S₄]^m+ (where m = 3, 2), and [Fe₆ S₆] ⁿ⁺ (where n = 5, 4) ions as models of the Desulfovibrio vulgaris iron–sulfur centers. Assuming that the redox potential mostly depends on the Heisenberg spin coupling and the resonance delocalization, we performed an analysis of the reduction process for the [Fe₄ S₃ O] ^3+/2+, [Fe₄ S₄] ^3+/2+, and [Fe₆ S₆] ^5+/4+ ions and showed that the redox potential can be calculated as a difference between average spin energies of the tetravalent and pentavalent double cubane superclusters. For the Heisenberg parameter of J₁ = 20 cm^-1, the redox potential amounts to about 0.03 V.It complies with close to zero experimental values of the redox potential.Electronic Supplementary Material: Supplementary material is available in the online version of this article at     

卤代硅烷分子的杂化轨道及结构与性质的关系研究

本文利用最大重迭方法,在分别考虑卤素配体的杂化及中央原子Si的d轨道杂化的基础上,计算了卤代硅烷系列分子实验构型下的杂化轨道,研究了卤代硅烷分子的NMR自旋偶合常数,IR伸缩频率和基团电负性与轨道成份的关系,较明确地反映了这类分子的化学键性质对分子谱学性质的影响。     

甲基丙烯酸(3-三甲氧基硅)丙酯-马来酸二丁基锡共聚物/二氧化硅杂化材料的制备

甲基丙烯酸（３ 三甲氧基硅）丙酯 马来酸二丁基锡共聚物／二氧化硅杂化材料的制备周文董建华丘坤元（北京大学化学与分子工程学院高分子科学与工程系，１００８７１北京）ＷｅｉＹｅｎ（危岩）（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，Ｄｒｅｘｅｌ...     

天然-合成高分子生物杂化材料在生物医学领域中的应用

综述了天然—合成高分子生物杂化材料在生物医学领域中的应用，并分析了它作为组织工程基质和药物载体的优点，指出生物杂化材料是生物医用材料的发展趋势。     

Synthesis and characterizations of novel, positively charged poly(methyl acrylate)-SiO2 nanocomposites

A series of positively charged poly(methyl acrylate) (PMA)-SiO₂ nanocomposites were prepared through the sol-gel process of positively charged alkoxysilane-containing polymer precursors. The precursors were synthesized by coupling different amounts of N-[3-(Trimethoxysilyl) propyl] ethylene diamine (A-1120) to poly(methyl acrylate) (PMA), followed by a quaternization reaction. These precursors were then hydrolyzed and condensed to generate PMA-SiO₂ hybrid sol-gel materials. IR and ¹H NMR measurements were conducted to confirm the chemical structure of the step products during the hybrids preparation. Thermal stabilities of the hybrids were conducted by DSC, TGA and their nanoscale microphase separation was distinguished by FE-SEM. Anion-exchange capacities of these nanocomposites were examined to be in the range of 0.19−1.20 mmol/g.     

Preparation and applications of novel fluoroalkyl end-capped oligomers/calcium carbonate nanocomposites

Calcium chloride reacted with sodium carbonate in the presence of a variety of self-assembled molecular aggregates formed by fluoroalkyl end-capped acrylic acid, 2-methacryloyloxyethane sulfonic acid, dimethylacrylamide, and acryloylmorpholine oligomers in aqueous solutions to afford the corresponding fluorinated oligomers/calcium carbonate composites in excellent to moderate isolated yields. These fluorinated calcium carbonate composites thus obtained were shown to have a good dispersibility not only in water but also in traditional organic media including fluorinated solvents. Dynamic light scattering measurements (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that these fluorinated composites are nanometer-size-controlled particles and well dispersed in these media. Cross-linked fluoroalkyl end-capped acrylic acid co-oligomer containing poly(oxyethylene) units was also applied to the preparation of new cross-linked fluorinated calcium carbonate nanocomposites under similar conditions. The obtained cross-linked fluorinated calcium carbonate nanocomposites were found to have an extremely higher dispersibility in aqueous and organic media including fluorinated solvents, compared to that of the corresponding fluoroalkyl end-capped oligomer nanocomposites. In particular, it was verified that these fluorinated calcium carbonate nanocomposites are applicable to the dispersion above poly(methyl methacrylate) (PMMA) film surface. Interestingly, field-emission SEM (FE-SEM) images of the cross-section of the modified PMMA films showed that calcium carbonate particles dispersed into these PMMA films could be arranged regularly above the modified film surface. More interestingly, cross-linked fluorinated oligomeric aggregates were able to provide suitable host moieties for the crystallization of calcium carbonate.     

Clay network in ABS-graft-MAH nanocomposites: Rheology and flammability

A melt blending method was used to prepare ABS/clay and ABS-g-MAH/clay nanocomposites. Cone calorimeter and advanced rheological extension system (ARES^©) were employed to measure flammability and dynamic rheological properties. The main aim is to establish a relationship between the clay network structure and flammability properties of polymer nanocomposites. From the results of dynamic rheological measurements, it was found that the clay network structure was formed in ABS-g-MAH/clay nanocomposites, which strongly affected the flammability properties of the nanocomposites. The clay network improves the melt viscosity and results in restraint on the mobility of the polymer chains during combustion, which leads to significant improvement of flame retardancy for the nanocomposites.     

Electrochemical behaviour of conducting polymers obtained into clay-catalyst layers. An in situ Raman spectroscopy study

In this paper we present the study of the electrochemical properties of the following conducting polymers: poly(o-anisidine), polyaniline and copolymers of aniline and o-anisidine obtained by a new synthetic method. The polymers are synthesized in free-of-acid conditions, using an activated montmorillonitic clay catalyst, known as Maghnite-H⁺ (Mag-H) as proton source. The electrochemical behaviour of poly(o-anisidine) created using Mag-H (PoANI-MagH) and their copolymers with aniline is quite different of those polymers created in HCl solution. In situ Raman data suggest that the structure of PoANI-MagH is a mixture of conducting (polyaniline-type) and redox (phenoxazine or phenazine-type) segments.     

SYNTHESIS AND ELECTRICAL PROPERTIES OF POLYIMIDE-Al2O3 COMPOSITES

Polyimide-alumina hybrid films were synthesized via in situ polymerization and thermal imidation process from a solution of polyimide precursor and nanosized alumina in N,N-dimethylacetamide, and the microstructure of the hybrid films was characterized by transmission electron microscope （TEM） and infra-red （IR） spectrometry. The dependence of thermal stability, tensile properties, dielectric properties and degradation endurance under corona on the nano-Al2O3 content of polyimide-alumina hybrid films was studied. The results show that with the increase of Al2O3 content, the thermal stability and the dielectric properties of the hybrids increase, while the tensile properties decrease. Better corona resistance can be achieved if the PI film is filled with α-Al2O3 nanometric particle.