Phase Structures of Nascent Polyethylene Powder Studied by Wideline Proton NMR

The wideline proton NMR spectra of polyethylene powder samples were analyzed in terms of contributions from three components： （1） a rigid part with immobile chains, （2） a soft region with liquid-like character which produces a Lorentzian contribution to the spectrum, and （3） an intermediate region in which the rotation of methylene groups about C-C bonds is partially hindered. The relative mass fractions as well as chain mobilities varied greatly among samples produced by different polymerization techniques. The NMR crystallinity agreed well with that estimated by WAXD and was much higher than DSC crystallinity, indicating an inclusion of the contribution from a crystalline-amorphous interphase. The crystalline defects in the rigid part could be significantly affected by processing parameters when employing the same type of polymerization technique. The intermediate region in the NMR spectra was analyzed according to the comparison between bimodal high density polyethylene and corresponding linear unimodal one. It was found that the mass fraction of the NMR interphase could be an indication of the percentage of tie molecules between crystalline lamellae and thus may significantly affect the mechanical properties of polymeric material.     

室温下聚乙烯及其共聚物的相结构动态变化

采用固体高分辨＾１３ＣＣＰ／ＭＡＳ方法跟踪测量了熔融淬火的聚乙烯样品及冷冻抽干的乙烯共聚物样品的相态结构在室温下随时间的变化，通过计算机拟合，观察到两种样品中的单斜晶、斜方晶并对该现象产生的机制给予了解释。     

History of the Irradiation Cross-Linking of Polyethylene

The formation of covalent C-C bonds or cross-links between the long chains in polyethylene (PE) by means of high energy irradiation was first deduced from changes in the stress-strain curves of the PE samples after irradiations in vacuo in the heavy water pile of the Argonne National Laboratory near Chicago in the academic year 1947-48. These cross-links can be produced in the solid sample at room temperature without change of shape of the sample. Such irradiated PE samples have a “memory effect” which has led to a large-scale application of the irradiation of PE to make heat shrinkable films and tubing.     

甲酸存在下 N-四氢苯并噻唑亚胺希夫碱的化学发光

新合成的N(2-四氢苯并噻唑)-2-羟基苯甲亚胺希夫碱与酸性高锰酸钾反应产生微弱的化学发光,甲酸的存在有显著的增敏作用。报道了其荧光光谱、化学发光光谱、紫外可见吸收光谱和化学发光动力学曲线,并建立了流动注射化学发光测定噻唑类希夫碱的方法。该法线性范围为1.0×10-7～8.0×10-5mol/L,检测限为5.0×10-8mol/L,对1.0×10-6mol/L噻唑类希夫碱11次平行测定的相对标准偏差为1.7％。     

几种常用荧光探针的化学发光成像研究

利用双(2,4,6)三氯苯基过氧化草酸酯(TCPO)-过氧化氢(H2O2)-咪唑-荧光探针的化学发光体系,研究了荧光探针化学发光成像,对几种常用的荧光探针(丁基罗丹明、罗丹明B、罗丹明6G、荧光素及异硫氰酸荧光素等)进行了定量分析。本方法具有高灵敏度、成像分析高通量等优点,线性范围宽,检出限达10-11mol/L。对四甲基异硫氰酸罗丹明(TRITC)标记的单克隆羊抗人IgG的化学发光成像分析,比相同条件下荧光成像的检出限低一个数量级。     

Hydrotropic Behavior of Sodium Salicylate in Presence of Additives

It is well known that, like surfactants aggregating at a certain concentration (called critical micelle concentration, CMC), hydrotropes also have minimum hydrotrope concentration (MHC). However, unlike surfactant CMC, this MHC value is usually very high, thereby reducing their application. In this paper we report the results of conductivity and viscosity measurements with a well known hydrotrope sodium salicylate (NaSal) solutions in presence and absence of additives (propanol, PrOH; butanol, BuOH; pentanol, PeOH and tetrabutylammonium bromide, Bu₄NBr). We have found that MHC value of NaSal decreases in presence of additives. Alcohols increase the hydrophobic interactions and decrease the MHC while Bu₄NBr, in addition to ameliorating the hydrophobic interactions, reduces the charge on head groups and MHC decreases more steeply in its presence. Increased solubility of riboflavin in NaSal containing the above additives corroborates the results.     

热分析法研究超高分子量聚乙烯的热熔性质

本文采用差热分析(DTA)、差示扫描量热法(DSC)研究了一系列以高效催化聚合而得的初生态超高分子量(M_w=70-315×10⁴)聚乙烯粉的热熔行为,还研究了在接近熔化或部分熔化的温度下恒温热处理对晶体性质的影响.     

Synthesis of N-Phenylanthranilic Acid Derivatives Using Water as Solvent in the Presence of Ultrasound Irradiation

Abstract

An improved synthesis of N-phenylanthranilic acid using water as solvent can be achieved by ultrasound irradiation. A number of N-phenylanthranilic acids were prepared in good yields in a very short reaction time.     

聚乙二醇相转移催化合成苊酮

研究了在铬酸酐、冰醋酸和相转移催化剂聚乙二醇存在下苊的氧化反应，较温和的条件可高产率地得到苊酮。     

Adsorption Kinetics of Some Polyethylene Glycol Octylphenyl Ethers Studied by the Fast Formed Drop Technique

The adsorption kinetics of Triton X-100 and Triton X-405 at solution/air and solution/hexane interfaces is studied by the recently developed fast formed drop technique. The dynamic interfacial tension of Triton X-100 and Triton X-405 solutions against hexane has been measured without preequilibration of the water and oil phases. It is found that the dynamic interfacial tension of Triton X-100 solutions passes through a minimum. This strange behavior is attributed to partial solubility of the surfactant in hexane. Such minima of the dynamic interfacial tension of Triton X-405 solutions have not been observed, which correlates well with the solubilities of both surfactants in hexane reported in the literature. The dynamic surface tension of solutions of both surfactants and the dynamic interfacial tension of Triton X-405 solutions are interpreted by the Ward and Tordai model for diffusion controlled adsorption. It is shown that proper interpretation of the experimental data depends on the type of isotherm used. More consistent results are obtained when the Temkin isotherm is used instead of the Langmuir isotherm. The results obtained with Triton X-100 at the solution/air interface confirm that the adsorption of this surfactant occurs under diffusion control. The adsorption of Triton X-405 at solution/air and at solution/hexane interfaces seems to occur under diffusion control at short periods of time, but under mixed (diffusion-kinetic) control at long periods of time. A hypothesis is drawn to explain this phenomenon by changes in the shape of the large hydrophilic heads of Triton X-405 molecules. Copyright 2000 Academic Press.     

Radiation-Induced Cross-Linking of Polyethylene in the Presence of Various Acetylenic Compounds

A study was made on the radiation-induced cross-linking reaction of polyethylene by exposing film samples to [ddot]Co γ-rays in vacuum or in the presence of various acetylenic compounds such as acetylene, its C₃ to C₅ higher derivatives, and their mixture with tetrafluoroethylene (TFE). The samples (0.2 mm thick) were found to decrease in weight when irradiated in vacuum, but to increase in the presence of the additives. The IR spectrum measurements of the resultant showed that the trans-vinylene unsaturation increased by the irradiation, especially in the presence of the C₃ to C₅ derivatives, and terminal vinyl increased markedly in acetylene. However, the formation of these unsaturations were depressed when the film was irradiated in the mixed gas with TFE. The rate of the cross-linking reaction was accelerated by the addition of acetylene-TFE, acetylene, trifluoromethyl-acetylene, perfluorobutyne-2, perfluorobutyne-2-TFE, and methylacetylene-TFE [G(cross-linking) = 4.4-1.2]. It was reduced with methylacetylene, butyne-1, butyne-1-TFE, pentyne-1, pentyne-1-TFE, pentyne-2, pentyne-2-TFE, [G(cross-linking) = 0.6-0.1]. On the basis of these experimental results a chain reaction scheme of the cross-linking is proposed, and it is discussed on the basis of the activation energy of the elementary reactions.     

Tailoring MWD of Bimodal Polyethylene in the Presence of Ziegler-Natta Catalyst

Summary: Linear poly (ethylene-co-1-butene) was produced through two-step polymerization in one reactor using a Ziegler-Natta catalyst, where in the first step, low molecular weight homopolymer of ethylene in the presence of hydrogen and in the next step, high molecular weight copolymer of ethylene with 1-butene in the absence of hydrogen were produced. Molecular weight distribution of bimodal polyethylene was tailored through adjustment of polymerization time of each stage and hydrogen concentration of the first stage. Increasing hydrogen concentration shifted the molecular weight distribution curve to the lower molecular weights and broadened molecular weight distribution while interestingly increased high molecular weight incorporation of copolymer produced in the second stage due to increasing of reaction rate in the second step. To achieve bimodal molecular weight distribution, the polymerization times of the first and the second steps, which are highly dependent on the amount of hydrogen, were adjusted properly. The effects of the mentioned parameters on the processability as well as rheological properties of some samples were investigated. The rheological results showed shear thinning behavior of all specimens and confirmed the changes in molecular weight and molecular weight distribution. It was also demonstrated that the melt miscibility between low molecular weight and high molecular weight fractions improved with increasing of chains having very low molecular weight.     

Study of Microwave Irradiation Polymerization in the Presence of Different Carriers

ABSTRACT

The influence of the presence of an inorganic carrier in the polymerization systems was investigated in this paper. Ten polymerization systems that contained different inorganic carriers such as Al₂O₃, SiO₂ were studied. The ten polymerization systems are dibutyltin Maleate (DBTM) and allyl thiourea (AT), DBTM and stearic acid vinyl ester (SAVE), SAVE and maleic anhydride (MH), SAVE and acrylamide (AM), itaconic acid (IA) and AM, SAVE and IA, AM and MH, IA, sodium acrylate (AANa), AM. It was found that the activity of monomer can be changed in the presence of a carrier and furthermore, the different species of carrier influence the activity of same monomer differently in the polymerization.     

Clouding Behavior and Thermodynamic Study of Nonionic Surfactants in Presence of Additives

The present study investigates the effect of different additives on the cloud point (CP) of nonionic surfactants Triton X-100 (TX-100) and Triton X-114 (TX-114) in aqueous solutions. The thermodynamic parameters of these mixtures were calculated at different additive concentrations. The cloud point of nonionic surfactants TX-100 and TX-114 decreased with the increment of electrolyte concentrations and increased with alcohol concentrations. The standard Gibbs free energy was found to be positive for both the surfactants, whereas the enthalpy and the entropy of the clouding phenomenon were found to be positive with alcohols and negative with electrolytes. The overall clouding process was endothermic for alcohols and exothermic for electrolytes.     

紫外辐照对高密度聚乙烯分子结构的影响

紫外线;官能化;紫外辐照对高密度聚乙烯分子结构的影响     

Synthesis of Additives from Montmorillonite to Modify High Density Polyethylene Final Properties

Summary: This work brings about the modification of sodium montmorillonite clay (MNa) by the cationic exchange with hexadecyltrimethylammonium to turn it into organophilic clay (MC₁₆). Subsequently, MC₁₆ was treated with silanes. Three silanes with functional groups of different chemical nature were used. The objective was to determine if the clay could affect high density polyethylene (HDPE) final behavior after being modified with each silane. The following silanes were used: Cl₂Si(CH₃)₂, Cl₂Si(CH₃)(C₆H₅) and Cl₂Si(C₆H₅)₂. Finally, in situ hydrolysis was carried out to generate the respective siloxanes. These materials were characterized by XRD, FTIR and GPC analyses. Each one of these additives was mixed using melt compounding processing in a Haake torque rheometer Rheocord 9000 equipped with a mix chamber and roller rotors at 100 rpm and 190 °C. All hybrids were characterized by XRD, SEM and thermogravimetric analyses. Barrier properties to cyclohexane were also determined by pervaporation experiments. Results from all studies showed that the addition of approximately 3 wt% of clay has changed the macroscopic properties of the above-mentioned composites, as compared with pure HDPE. This can be explained considering the different polymer/filler interactions which take place in each system.     

Low-Temperature Radiation-Initiated Hydrobromination of Allene as Studied by Kinetic Calorimetry

The spontaneous and radiation-initiated cryochemical reactions of allene hydrobromination were studied. The spontaneous hydrobromination of allene proceeded in the liquid phase in the temperature range 170–280 K, yielding primarily 2-bromopropene. Postradiation hydrobromination was observed at much lower temperatures (80–120 K) with the formation of allyl bromide and 1,3-dibromopropane.