Silicone‐based impact modifiers for poly(vinyl chloride), engineering resins,and blends

Silicone‐based impact modifiers were prepared in a previous study. The modifiers were composed of silicone/acrylic rubber cores and grafted acrylic shells. They improved the toughness of poly(vinyl chloride) (PVC) and poly(methyl methacrylate). The silicone emulsion that was used to produce the silicone‐based impact modifiers was prepared via two routes: emulsion polymerization and bulk polymerization of octamethyltetracyclosiloxane. Many silicone‐based impact modifiers were produced that had different silicone/acrylic rubber characteristics. Through a toughness examination of modified PVC, the best composition of the silicone‐based impact modifiers was obtained, and the silicone content in the rubber composition was 25 wt %. The morphology of the silicone‐based impact modifiers, determined by transmission electron microscopy, was as follows: core and second shell polymers were mainly poly(butyl acrylate), and the first shell polymer was silicone. The silicone‐based impact modifiers were blended with engineering resins such as PVC, polycarbonate (PC), poly(butylene terephthalate) (PBT), and PC/PBT mixtures. The impact strength under standard conditions and after weathering test conditions for blends of the silicone‐based impact modifiers were investigated with respect to two commercially available acrylic and methyl methacrylate/butadiene/styrene impact modifiers. The results showed good weatherability and good toughness under low‐temperature conditions for the silicone‐based impact modifiers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1112–1119, 2004     

聚氯乙烯表皮成分对加成型硅橡胶固化的影响

采用流变学方法研究了双组分加成型硅橡胶在不同聚氯乙烯(PVC)表皮上的固化动力学,并利用红外光谱、核磁共振波谱、电感耦合等离子体质谱仪等手段分析了PVC表皮成分,以确定导致双组分加成型硅橡胶不固化的具体原因。 结果表明,PVC表皮中导致硅橡胶不固化的主要元素为P元素。 在固定硅橡胶厚度为1 mm的情况下,当PVC表皮中的P元素质量分数低于3×10^-3%时,浇注在其上的双组分加成型硅橡胶依然能固化;而当PVC表皮中的P元素质量分数超过约2.4×10^-2%时,虽然浇注在其上的双组分加成型硅橡胶的中间层依然能固化,但与PVC表皮接触部分的硅橡胶不固化,且不固化层厚度随P元素质量分数增加而增加。 本文还研究了在P元素质量分数低于3×10^-3%的PVC表皮上,降低硅橡胶厚度至微米级时的固化行为,在P元素质量分数低于3×10^-3%的PVC表皮上,当硅橡胶厚度低于2 μm时,硅橡胶出现不完全固化现象。 双组分加成型硅橡胶在含有P元素的PVC表皮表面的固化行为主要是由硅橡胶样品中铂催化剂总含量及PVC表皮中的P元素含量确定的,同时也会受到双组分加成型硅橡胶反应速率以及铂催化剂、P元素在硅橡胶中的扩散速率的影响。     

质子辐照对有机硅树脂增强甲基硅橡胶的性能损伤及机理

硅橡胶具有优良的电绝缘性以及耐高低温、耐电晕、耐化学腐蚀、耐大气老化、耐臭氧和耐辐射等性能，近年来在航天领域得到了广泛应用．在宇宙空间的带电粒子如质子、电子等的辐照作用下，硅橡胶会发生性能退化，其质损率上升，产生析气现象，从而直接影响航天器的可靠性和寿命．自80年代以来，人们就对不同辐照源及不同粒子注量对硅橡胶材料的影响进行了研究，但直到近几年才将研究热点转向辐照场中硅橡胶的性能退化及微观结构的演变规律，其辐照环境大多集中于γ射线、Si^＋和F^＋离子、He^2＋离子等．对于空间环境下带电粒子辐照对硅橡胶材料的影响，国外由于相应的研究工作保密性强，报道甚少；国内哈尔滨工业大学则对我国自行研制的白炭黑增强空间级甲基硅橡胶质子辐照作用后的性能与微观结构的变化做了较为深入的研究。     

A novel phase-change composites based on silicone rubber containing energy-storage microcapsules

A novel phase-change composites based on silicone rubber (MVQ) containing n-octadecane/poly (styrene-methyl methacrylate) microcapsules were successfully obtained by mixing energy-storage microcapsules into MVQ matrix using three preparation methods. The effect of microcapsules content on thermal property of the composites was investigated by thermogravimetric analysis. The mechanical properties of the composites prepared by three methods were also investigated. The morphology and thermal properties of the composites were characterized by scanning electron microscopy (SEM), differential scanning calorimetry, and thermal response. Thermal and mechanical properties of the composites were excellent when the microcapsules were added into room temperature vulcanized silicone rubber with 2 phr (per hundred rubber) content and cured at room temperature. The composites were proved to have good energy-storage performance with 67.6 J g^?1 enthalpy value.     

Application of intercalated compound of montmorillonite and N,N′-diphenyl-p-phenylenediamine to antioxidant for rubber materials

To extend the lifetime of rubber materials, the intercalated compound consisting of N, N-diphenyl-p-phenylenediamine (DPD) as guest molecule and montmorillonite as host layer was added to chloroprene rubber (CR) and acrylonitrile-butadiene rubber (NBR). These rubber samples were either immersed in a mixture of isooctane and toluene or kept at 140°C in air, and subjected to ozone aging tests. The residual DPD in CR was analysed by high pressure liquid chromatography. Their results were compared with the rubbers of a standard composition, including DPD alone. The solvent-immersed CR containing the intercalated compounds showed more improved ozone-cracking resistance than solvent immersed CR of the standard composition. The residual DPD in CR containing the intercalated compound was more than that in CR of standard composition. However, no significant difference between the specimens containing intercalated compound and those of the standard composition was observed for the solvent-immersed NBR, heat-treated NBR and heat-treated CR.     

EFFECTS OF SOME PHENYLETHYNYLSILICON COMPOUNDS ON HEAT-CURABLE SILICONE RUBBER Ⅲ 1, 1, 3, 3-TETRAMETHYL-1, 3-DIPHENYLETHYNYL-DISILOXANE*

We have shown that some phenylethynylsilicon compounds are good cure crosslinkersof heat-curable silicone rubber(HCSR). In this paper the effects of 1, 1, 3, 3-tetramethyl-1, 3-diphenylethynyldisiloxane (TMDPDS) as a crosslinker on HCSR were studied. Thevulcanizates with fine mechanical properties could be obtained with suitable amounts ofTMDPDS. Sol fractions, and crosslinking density of vulcanizates and vulcanizationretardation effect of TMDPDS on hydrosilation curing silicone rubber were also discussed.     

Difference in bound rubber formation of silica and carbon black with styrene‐butadiene rubber

Formation of bound rubber is affected by the physical structure and surface chemistry of filler and the property of rubber. Variation of the bound rubber formation in styrene‐butadiene rubber compounds filled with silica and/or carbon black was studied. Influence of temperature on extraction of loosely bound rubber was also investigated. For the both silica and carbon black‐filled compounds, the bound rubber content increases with increase in the silica content ratio. The bound rubber content decreases with increasing the extracting temperature. The loosely bound rubber content of the silica‐filled compound is higher than that of the carbon black‐filled one. Activation energy for the extraction of the unbound and loosely bound rubbers becomes higher as the total filler content increases. The activation energy of the silica‐filled compound is higher (almost double the value) than for the carbon black‐filled one. Copyright­© 2002 John Wiley & Sons, Ltd.     

Effect of 200 keV proton irradiation on the properties of methyl silicone rubber

The effects of 200 keV proton irradiation on methyl silicone rubber were studied. The changes in surface morphology, mechanical properties, cross-linking density, glass transition temperature, infrared attenuated total reflection spectrum and mass spectrum indicated that, at lower fluence, the proton irradiation induced cross-linking, resulting in an increase in tensile strength and hardness of the methyl silicone rubber. However, at higher proton fluence, radiation-induced degradation, which decreased the tensile strength and hardness, became dominant. A macromolecular-network destruction model for silicone rubber irradiated with protons was proposed.     

Preparation and properties of dynamically cured poly(vinylidene fluoride)/silicone rubber blends

Blends of poly(vinylidene fluoride) (PVDF) and silicone rubber (SR) were prepared through dynamic vulcanization. The effects of SR content on crystallization behavior, rheology, dynamic mechanical properties and morphology of the blends were investigated. Morphology characterization shows that the crosslinked spherical SR particles with an average diameter of 2-4 μm form a “network” in the PVDF continuous phase. The dynamic mechanical properties indicate the interface adhesion between PVDF and rubber phase is improved by the dynamic vulcanization. The rheology study shows that with the increase of rubber content the blends pseudoplastic nature is retained, while the viscosity increases, and hence the processability is less good. The incorporation of SR phase promotes the nucleation process of PVDF, leading to increased polymer crystallization rate and crystallization temperature. However, a higher content of SR seems to show a negative effect on the crystallinity of the PVDF component.     

Synthesis of diazafluorene- and diazafluorenone-N,N′-dioxides using HOF·CH3CN

A variety of diazafluorenes and diazafluorenones were oxidized using the HOF·CH₃CN complex to form the corresponding N,N′-dioxide derivatives under mild conditions. The products exhibit red-shift absorptions in the UV/visible spectrum relative to the parent compounds. Many such oxidations could not be achieved with any other oxygen-transfer agent.     

Synthesis,Biological Evaluation,and Structure–Activity Relationships of 4-Aminopiperidines as Novel Antifungal Agents Targeting Ergosterol Biosynthesis

The aliphatic heterocycles piperidine and morpholine are core structures of well-known antifungals such as fenpropidin and fenpropimorph, commonly used as agrofungicides, and the related morpholine amorolfine is approved for the treatment of dermal mycoses in humans. Inspired by these lead structures, we describe here the synthesis and biological evaluation of 4-aminopiperidines as a novel chemotype of antifungals with remarkable antifungal activity. A library of more than 30 4-aminopiperidines was synthesized, starting from N-substituted 4-piperidone derivatives by reductive amination with appropriate amines using sodium triacetoxyborohydride. Antifungal activity was determined on the model strain Yarrowia lipolytica, and some compounds showed interesting growth-inhibiting activity. These compounds were tested on 20 clinically relevant fungal isolates (Aspergillus spp., Candida spp., Mucormycetes) by standardized microbroth dilution assays. Two of the six compounds, 1-benzyl-N-dodecylpiperidin-4-amine and N-dodecyl-1-phenethylpiperidin-4-amine, were identified as promising candidates for further development based on their in vitro antifungal activity against Candida spp. and Aspergillus spp. Antifungal activity was determined for 18 Aspergillus spp. and 19 Candida spp., and their impact on ergosterol and cholesterol biosynthesis was determined. Toxicity was determined on HL-60, HUVEC, and MCF10A cells, and in the alternative in vivo model Galleria mellonella. Analysis of sterol patterns after incubation gave valuable insights into the putative molecular mechanism of action, indicating inhibition of the enzymes sterol C14-reductase and sterol C8-isomerase in fungal ergosterol biosynthesis.     

Solubility study of curatives in various rubbers

The previous works on solubility of curatives in rubbers were mainly carried out in natural rubber. Not too much information available on dissimilar rubbers and this is important because most of the compounds today are blends of dissimilar rubbers. Although solubility can be expected to certain level by the previous studies, the current work provides a much precise view in the solubility behavior of curatives. Solubility of sulphur and several accelerators N-cyclohexylbenzothiazole-2-sulphenamide (CBS), N-dicyclohexylbenzothiazole-2-sulphenamide (DCBS), and 2-mercaptobenzothiazole (MBT) is measured in dicumyl peroxide vulcanised Styrene-Butadiene rubber (SBR), Acrylonitrile-Butadiene rubber (NBR) and Ethylene-Propylene-Diene rubber (EPDM) rubber at room temperature and at 60 °C. The experimental results can be correlated with the calculated solubility parameters δ, as determined using the method of Hoftijzer and Van Krevelen. Results of are used to judge the solubility of curatives in a specific rubber in blends.     

Antimicrobial properties of Ag loaded zeolite polyester polyurethane and silicone rubber and long-term properties after exposure to in-vitro ageing

In biomedical applications, tubes (e.g. catheters etc.) are commonly produced from polyurethane (PU) and silicone rubber which are known to be biocompatible materials. Several studies have shown that tubes, which are connected to the body (invasive) (especially urinary, tracheotomy and central venous catheters) are associated with infections. The present study reports the development of a new method aiming at obtaining antibacterial properties for PU and silicone rubber by mixing respective material with a natural antibacterial agent (Ag+ loaded zeolite) in different weight fractions. The influence of the zeolite content on the antimicrobial properties were analysed by exposure to bacteria (ISO 22196) and mixtures of fungi (ISO 846). The materials were also subject to artificial body fluids (Artificial Lysosomal Fluid (ALF) and Gamble’s solution) for periods up to three months and the subsequent changes in the chemical properties after in-vitro exposure were determined by Matrix Assisted Laser Deposition/Ionization Time Of Flight Mass Spectrometry (MALDI-TOF MS) and Attenuated Total Reflection Fourier Transform Infra Red spectroscopy (ATR-FTIR). It was established that the antimicrobial effect of the materials increased with the increase of the zeolite content. The wettability of the materials was found to decrease significantly during the in-vitro exposure, but this could not be correlated to the zeolite content. In the PU samples, the formation of free carbonyl and -OH groups was observed, which corresponds to oxidative degradation. In case of the silicone rubber the ratio of cyclic PDMS to linear PDMS (H, CH3 and dimethyl terminated) decreased, which indicates a change in the concentration of the compounds. The formation and increase of the O-H bond during the exposure was also confirmed by the infrared spectra of the material which corresponds to hydrolysis of the silicone rubber.     

High performance liquid chromatographic determination of diazinon, permethrin, DEET (N, N-diethyl-m-toluamide), and their metabolites in rat plasma and urine

A rapid method was developed for the analysis of the insecticide (A) diazinon (O,O-diethyl O-2-isopropyl-6-methylpyridimidinyl) phosphorothioate, its metabolites (B) diazoxon (O,O-diethyl O-2-isopropyl-6-methylpyridimidinyl) phosphate, and (C) 2-isopropyl-6-methyl-4-pyrimidinol, the insecticide (D) permethrin [3-(2,2-dichloro-ethenyl)-2,2-dimethylcyclopropanecarboxylic acid (3-phenoxyphenyl)methylester], its metabolites (E) m-phenoxybenzyl alcohol, and (F) m-phenoxybenzoic acid, the insect repellent (G) DEET (N,N-diethyl-m-toluamide), and its metabolites (H) m-toluamide and (I) m-toluic acid in rat plasma and urine. The method is based on using C₁₈ Sep-Pak cartridges (Waters Corporation, Milford, Mass., U.S.A.) for solid phase extraction and high performance liquid chromatography with a reversed phase C₁₈ column, and absorbance detection at 230 nm for compounds A, B, and C, and at 210 nm for compounds D–I. The compounds were separated using a gradient from 1% to 99% acetonitrile in water (pH 3.0) at a flow rate ranging between 1 and 1.7 mL/min in a period of 17 min. The limits of detection were ranged between 20 and 100 ng/mL, while limits of quantification were 80–200 ng/mL. The relationship between peak areas and concentration was linear over a range of 100–1000 ng/mL. This method was applied to determine the above insecticides and their metabolites following dermal administration in rats.     

The physical aging phenomenon of 6FDA‐durene polyimide hollow fiber membranes

The aging phenomenon of asymmetric 6FDA‐durene polyimide hollow fibers spun with different shear rates for gas separation has been investigated. The permeances and selectivities of different gases, such as H₂, O₂, N₂, CH_4, and CO₂, were experimentally determined as a function of time for around five months at room temperature. It was found that the gas permeation fluxes of the uncoated and silicone rubber‐coated hollow fibers decreased significantly during the first 30 days following fabrication and then slightly deteriorated thereafter. In the early stage of aging, because of different molecular orientations and skin morphologies induced by shear rates, the percentage of permeance drop for uncoated fibers increased with increasing shear rates, then decreased with increasing shear rates. The permeance of 6FDA‐durene hollow fibers coated with silicone rubber dropped more significantly than the uncoated fibers, implying that silicone rubber coating did affect the aging behavior. This might be due to the fact that silicone rubber layer hindered the molecular relaxation and tightened interface molecules between the dense selective layer and silicone rubber, thus the selectivity increased with aging. Thermal analysis data suggest two processes occurring simultaneously during the aging: one is the relaxation of shear oriented chains, and the other is the densification of chain packing through the reduction of interstitial space among chains. The former has been confirmed by an increase in CTE, while the latter was confirmed by an increase in the peak of β‐relaxation temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 765–775, 2000     

Acetylcholinesterase-Inhibiting Activity of Salicylanilide <em>N</em>-Alkylcarbamates and Their Molecular Docking

A series of twenty-five novel salicylanilide N-alkylcarbamates were investigated as potential acetylcholinesterase inhibitors. The compounds were tested for their ability to inhibit acetylcholinesterase (AChE) from electric eel (Electrophorus electricus L.). Experimental lipophilicity was determined, and the structure-activity relationships are discussed. The mode of binding in the active site of AChE was investigated by molecular docking. All the discussed compounds expressed significantly higher AChE inhibitory activity than rivastigmine and slightly lower than galanthamine. Disubstitution by chlorine in C'_(3,4) of the aniline ring and the optimal length of hexyl-undecyl alkyl chains in the carbamate moiety provided the most active AChE inhibitors. Monochlorination in C'₍₄₎ exhibited slightly more effective AChE inhibitors than in C'₍₃₎. Generally it can be stated that compounds with higher lipophilicity showed higher inhibition, and the activity of the compounds is strongly dependent on the length of the N-alkyl chain.     

Trennung,Identifizierung und Bestimmung von Bactericiden auf der Basis von halogenierten Aromaten mittels Gas-Chromatographie

The separation of a mixture of 22 bactericides has been achieved by gas chromatography on columns with silicone rubber W-982 as stationary phase with temperatures between 100° and 300°C. The unchanged compounds as well as their silylation products have been used. The latter are more conveniently used especially for the quantitative determination. To be able to calculate the retention indices after Kovats gas chromatography has been performed isothermally at 180°C for the more volatile compounds and at 250°C for all other bactericides.The retention indices obtained under these conditions are tabulated together with the limits of detection.     

Graft copolymers of natural rubber and poly(dimethyl(acryloyloxymethyl)phosphonate) (NR-g-PDMAMP) or poly(dimethyl(methacryloyloxyethyl)phosphonate) (NR-g-PDMMEP) from photopolymerization in latex medium

Graft copolymers of natural rubber and poly(dimethyl(acryloyloxymethyl)phosphonate) (NR-g-PDMAMP), and natural rubber and poly(dimethyl(methacryloyloxyethyl)phosphonate) (NR-g-PDMMEP), were prepared in latex medium via a “grafting from” methodology based on the photopolymerization of dimethyl(acryloyloxymethyl)phosphonate (DMAMP) and dimethyl(methacryloyloxyethyl) phosphonate (DMMEP), respectively, used as phosphorus-containing monomers. The grafting polymerization was initiated from N,N-diethyldithiocarbamate groups previously bound in side position of the rubber chains. The effects of monomer concentration on monomer conversion and grafting rate were investigated, showing that conversion and grafting rate increased with increasing monomer concentration and reaction time. Highest conversions and grafting rates were obtained with a molar ratio [DMAMP]/[initiating units] = 7 for a reaction time of 180 min. Calculation of the graft average length () from ¹H NMR spectra of the synthesized graft copolymers showed values were in the range of 9-73. Visualizations of NR-g-PDMAMP and NR-g-PDMMEP latices by Transmission Electron Microscopy (TEM) showed that they exhibit core-shell morphologies. Degradation of NR-g-PDMAMP and NR-g-PDMMEP occurred in two steps: decomposition of dimethylphosphonate-functionalized grafts took place prior to the second step corresponding to the decomposition of NR backbone, but the degradation temperature of this last step was higher than that of pure NR.     

某航空橡胶密封材料成分分析

采用红外光谱法对某航空橡胶密封材料成分进行定性分析,结果表明,该样品的胶种为硫化甲基硅橡胶,有机助剂为邻苯二甲酸二辛酯(DOP),无机灰分为氧化锌、硫酸钙,含量为4%。使用红外光谱法分析航空密封橡胶成分是一种经济且快速的分析方法。     

<em>N</em>-Substituted 5-Chloro-6-phenylpyridazin-3(2<em>H</em>)-ones: Synthesis, Insecticidal Activity Against <em>Plutella xylostella </em>(L.) and SAR Study

A series of N-substituted 5-chloro-6-phenylpyridazin-3(2H)-one derivatives were synthesized based on our previous work; all compounds were characterized by spectral data and tested for in vitro insecticidal activity against Plutella xylostella. The results showed that the synthesized pyridazin-3(2H)-one compounds possessed good insecticidal activities, especially the compounds 4b, 4d, and 4h which showed > 90% activity at 100 mg/L. The structure-activity relationships (SAR) for these compounds were also discussed.