Autooxidation of Oriented Polyolefins

Abstract

The effect of the chemical structure of the polymer on its reactivity in the oriented state is studied, and causes of the effect of orientation drawing of polyolefins on the oxidation kinetics are identified.

The orientation drawing of the polymer is shown to be dependent on the nature of the latter which can either delay or accelerate the oxidation process. The effect of a delayed rate of oxidation for the samples of one drawing degree is determined by the nature of the side substitute in the monomeric link of the polymer.

The effect of the orientation drawing of the polymer on the change of parameters of oxidation (k ₂ k ₆ ^?0.5 [RH]), a decrease of the coefficients of solubility and diffusion of oxygen as well as the change in the polymer structure depending on its nature are considered.

Analysis of structural changes in the polymers due to orientation has shown that drawing of the polymer can result in localization of oxidation in defected zones of amorphous areas isolated from each other by transition chains in extremely straightened conformation. In this case, the oxidation kinetics of oriented polyolefins can be described with the use of postulates of the “zone” model developed by Yu. A. Shlyapnikov. Evaluation of the kinetic parameters of oxidation (k _2eff, k _6eff, θ) with the use of this model is made.

It is shown that the effect of the nature of the polymer is due to a change in activity of the C?H bonds participating in the oxidation process, peculiar features of changes in the structure and physical properties of the polymer in the process of orientation drawing, in terms of the “zone” model, to the rate of the expansion of the oxidation center, that is, the nature of the polymer determines the parameters k _2eff, k _6eff, θ in the oriented sample.     

Activity and Mechanism of Action of Thio and Dithiobisphenols in the Stabilization of Polyolefins

Abstract

Diphenol substituted sulfides have been studied as stabilizers poypropylene against thermal oxidation. Both phenol groups of antioxidants are reacting with oxidation reaction centres, the sulfide group reacting with hydroperoxides.

The reaction of phenol-substituted disulfides with tert-butylhydroperoxide was also studied.

The role of unstable sulfur-containing intermediates is discussed.     

气体在水中的分子动力学模拟

采用分子动力学（ＭＤ）模拟的方法在常温及工业应用背景条件下对ＣＨ４、ＮＨ３、ＣＯ２、Ｏ２这些气体在水中的结构及扩散情形进行了研究。ＭＤ模拟可以为这些涉及到气体在水中的工业应用情形的机理提供分子水平的解释,同时ＭＤ模拟还可为一些不易实验测定扩散性质的体系提供工程初步设计和过程开发所需的数据。     

Contact Oxidation and Adhesive Interaction of Polyolefins with Metals

Polymer-metal systems: adhesive joints of metals, metal-polymer composites, polymeric coatings on metals etc., are of great practical interest. The polyolefin-based systems (large supply, widespread, cheap polymers, distinguished by high chemical resistance, anticorrosive capacity and other valuable properties) and steel (including steel of the common grades, which are in great need of rust protection) are wisely used. One of the basic requirements, guaranteeing high serviceability of the abovementioned systems, is a strong and durable adhesive interaction between polymer and metal. In this paper, the most essential research results, obtained in our laboratory, in the field of controlling the processes of adhesive interaction between polyolefin melts and steel surfaces, have been generalized (for more detail, see Ref. 1).     

Contact Oxidation and Adhesive Interaction of Polyolefins with Metals

Polymer-metal systems: adhesive joints of metals, metal-polymer composites, polymeric coatings on metals etc., are of great practical interest. The polyolefin-based systems (large supply, widespread, cheap polymers, distinguished by high chemical resistance, anticorrosive capacity and other valuable properties) and steel (including steel of the common grades, which are in great need of rust protection) are wisely used. One of the basic requirements, guaranteeing high serviceability of the abovementioned systems, is a strong and durable adhesive interaction between polymer and metal. In this paper, the most essential research results, obtained in our laboratory, in the field of controlling the processes of adhesive interaction between polyolefin melts and steel surfaces, have been generalized (for more detail, see Ref. 1).     

NPT系综分子动力学模拟水的密度和扩散系数

采用常温常压(NPT)系综分子动力学方法模拟了298.15K、0.1013MPa条件下水的密度和自扩散系数,模拟结果与实验值一致,相对误差分别为1.74%和3.83%。     

受限于碳纳米管中水分子微观结构的分子动力学模拟研究

利用分子动力学模拟研究受限于不同管径中水分子的微观结构,改变温度,做出受限水分子的径向分布函数图,并对比说明。通过做水分子在碳纳米管内的均方位移与时间关系图,利用Einstein法算出不同管径中水分子的扩散系数,与利用Knudsen扩散公式计算出的水分子的扩散系数进行比较。     

Assessing the effect of molecular weight on the kinetics of backbone scission reactions in polyethylene using Reactive Molecular Dynamics

Kinetics of polymer bond scission, the initial step in thermal decomposition of polyethylene and other vinyl polymers, was investigated as a function of the number of repeat units using an improved Reactive Molecular Dynamics (RMD) approach, which is introduced here. The rate of scission per bond is shown to depend on the degree of polymerization, an effect not captured by the conventional practice of modeling polymer decomposition with small-molecule Arrhenius parameters. In the new approach, implemented in an open-source C++ code RxnMD, well-behaved reactive force fields are generated using switching functions that activate and attenuate terms obtained from a conventional, non-reactive force field. In this way, predefined reaction types are modeled accurately by interpolating smoothly between non-reactive potential energy terms describing reactants, transition states, and products.     

Effects of Concentrations on the Transdermal Permeation Enhancing Mechanisms of Borneol: A Coarse-Grained Molecular Dynamics Simulation on Mixed-Bilayer Membranes

Borneol is a natural permeation enhancer that is effective in drugs used in traditional clinical practices as well as in modern scientific research. However, its molecular mechanism is not fully understood. In this study, a mixed coarse-grained model of stratum corneum (SC) lipid bilayer comprised of Ceramide-N-sphingosine (CER NS) 24:0, cholesterol (CHOL) and free fatty acids (FFA) 24:0 (2:2:1) was used to examine the permeation enhancing mechanism of borneol on the model drug osthole. We found two different mechanisms that were dependent on concentrations levels of borneol. At low concentrations, the lipid system maintained a bilayer structure. The addition of borneol made the lipid bilayer loosen and improved drug permeation. The “pull” effect of borneol also improved drug permeation. However, for a strongly hydrophobic drug like osthole, the permeation enhancement of borneol was limited. When most borneol molecules permeated into bilayers and were located at the hydrophobic tail region, the spatial competition effect inhibited drug molecules from permeating deeper into the bilayer. At high concentrations, borneol led to the formation of water pores and long-lived reversed micelles. This improved the permeation of osthole and possibly other hydrophobic or hydrophilic drugs through the SC. Our simulation results were supported by Franz diffusion tests and transmission electron microscope (TEM) experiments.     

Study on the Characteristics of Gas Molecular Mean Free Path in Nanopores by Molecular Dynamics Simulations

This paper presents studies on the characteristics of gas molecular mean free path in nanopores by molecular dynamics simulation. Our study results indicate that the mean free path of all molecules in nanopores depend on both the radius of the nanopore and the gas-solid interaction strength. Besides mean free path of all molecules in the nanopore, this paper highlights the gas molecular mean free path at different positions of the nanopore and the anisotropy of the gas molecular mean free path at nanopores. The molecular mean free path varies with the molecule’s distance from the center of the nanopore. The least value of the mean free path occurs at the wall surface of the nanopore. The present paper found that the gas molecular mean free path is anisotropic when gas is confined in nanopores. The radial gas molecular mean free path is much smaller than the mean free path including all molecular collisions occuring in three directions. Our study results also indicate that when gas is confined in nanopores the gas molecule number density does not affect the gas molecular mean free path in the same way as it does for the gas in unbounded space. These study results may bring new insights into understanding the gas flow’s characteristic at nanoscale.     

聚合物阻垢剂阻垢机理的分子动力学研究

用分子模拟方法构建了碳酸钙六方体晶胞结构,优化了丙烯酸与丙烯酸甲酯共聚物的构型,模拟了单体不同配比时各共聚物与碳酸钙晶体之间的相互作用,并计算了其作用能量的变化。计算结果显示:所有阻垢剂分子都逐渐接近方解石晶体,活性基团占据晶体的晶格生长点或嵌入晶体内部,同时伴随小幅度的分子结构变形,抑制晶体成核而有效阻止垢的形成,或使晶体内部形成空洞,导致晶格畸变而使垢松软。同时随着丙烯酸单体的比例增大,阻垢作用更明显。     

分子动力学方法在火炸药研究中的应用进展

概述了国内外分子动力学方法在单体炸药、混合炸药和固体推进剂研究中的应用进展,并分析了在应用中存在的问题以及发展前景,为该领域科研人员利用该方法开展火炸药研究提供参考。     

Structure and composition of the surface layer in polymers modified by elemental fluorine

A model is proposed for the layered structure of a polymer surface modified by elemental fluorine mixed with helium. The composition of the modified surface layer has been determined, and the thermodynamic compatibility of the surface layer, transition layer, and unmodified bulk of the polymer has been studied. The thickness of the modified layers has been calculated as a function of the fluorination conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 897–902, 2005     

Role of Guest Molecules on the Hydrate Growth at Vapor‐Liquid Interfaces

Systematic molecular dynamics simulations have been performed to illustrate the roles of guest molecules played in the process of hydrate growth at vapor‐liquid interfaces. In our simulations, guest molecules are represented by a commonly used single‐site Lennard–Jones model, and the roles of guest molecules on hydrate growth have been investigated separately from the effect of water–guest molecule attractive interaction ε and that of molecular size σ, respectively. Our simulation results demonstrate that the water‐guest molecule attraction regulates the pathway and rate of nucleus growth, whereas the size of guest molecules determines the dynamically preferable structure. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2621–2629, 2013     

超临界水中气体扩散系数的分子动力学模拟

采用分子动力学（MD）方法计算T＝703.2-763.2K,p=30-45MPa范围内,氧气和氮气在超临界水中的无限稀释扩散系数。计算结果表明,在超临界条件下的扩散系数较常温常压下要大1－2个数量级。扩散系数随温度的升高而增大,随压力的增高而降低,且氧的扩散系数稍大于氮的扩散系数。     

不同温度下RDX晶体力学性能的MD模拟

为探讨单体炸药RDX的静态力学性能随温度变化的规律,用分子动力学(MD)方法和COMPASS力场,在等温等压系综下,对其作多种温度(195～445 K)下的周期性模拟计算,由静态力学分析求得弹性系数、模量和泊松比.结果表明,在195～345 K时,体系的刚性和弹性随温度的增加而下降;但当温度达到345K时,体系的刚性和弹性几乎不变.     

Thermodynamic Insight into the Effects of Water Displacement and Rearrangement upon Ligand Modifications using Molecular Dynamics Simulations

Computational methods, namely molecular dynamics (MD) simulations in combination with inhomogeneous fluid solvation theory (IFST) were used to retrospectively investigate various cases of ligand structure modifications that led to the displacement of binding site water molecules. Our findings are that water displacement per se is energetically unfavorable in the discussed examples, and that it is merely the fine balance between change in protein–ligand interaction energy, ligand solvation free energies, and binding site solvation free energies that determine if water displacement is favorable or not. We furthermore evaluated if we can reproduce experimental binding affinities by a computational approach combining changes in solvation free energies with changes in protein–ligand interaction energies and entropies. In two of the seven cases, this estimation led to large errors, implying that accurate predictions of relative binding free energies based on solvent thermodynamics is challenging. Nevertheless, MD simulations can provide insight regarding which water molecules can be targeted for displacement.     

PP／MWNT注塑制品的取向结构和性能研究

研究了多壁碳纳米管（MWNT）的表面改性和取向结构对PP／MWNT注射制品的拉伸性能的影响。结果表明，碳管的表面接枝改性能够提高聚合物基体和碳管之间的界面粘接作用，为应力从基体到碳管的有效传递提供了有利条件；同时，在基体取向的情况下，注射制品的拉伸性能产生了大幅度的提高。     

Effects of the Protonation State of Titratable Residues and the Presence of Water Molecules on Nocodazole Binding to β‐Tubulin

Regulation of microtubule assembly by antimitotic agents is a potential therapeutic strategy for the treatment of cancer, parasite infections, and neurodegenerative diseases. One of these agents is nocodazole (NZ), which inhibits microtubule polymerization by binding to β‐tubulin. NZ was recently co‐crystallized in Gallus gallus tubulin, providing new information about the features of interaction for ligand recognition and stability. In this work, we used state‐of‐the‐art computational approaches to evaluate the protonation effects of titratable residues and the presence of water molecules in the binding of NZ. Analysis of protonation states showed that residue E198 has the largest modification in its pK_a value. The resulting E198 pK_a value, calculated with pH‐REMD methodology (pK_a=6.21), was higher than the isolated E amino acid (pK_a=4.25), thus being more likely to be found in its protonated state at the binding site. Moreover, we identified an interaction between a water molecule and C239 and G235 as essential for NZ binding. Our results suggest that the protonation state of E198 and the structural water molecules play key roles in the binding of NZ to β‐tubulin.