Computational and Theoretical Polymer Science最新文献_第4页

Simulation of the random scission of C–C bonds in the initial stage of the thermal degradation of polyethylene 聚乙烯热降解初期C-C键随机断裂的模拟

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00078-1

P. Doruker , Y. Wang , W.L. Mattice

{"title":"Simulation of the random scission of C–C bonds in the initial stage of the thermal degradation of polyethylene","authors":"P. Doruker , Y. Wang , W.L. Mattice","doi":"10.1016/S1089-3156(99)00078-1","DOIUrl":"10.1016/S1089-3156(99)00078-1","url":null,"abstract":"<div><p>We performed molecular dynamics simulations to analyze the initial stage of the thermal degradation of polyethylene, which is dominated by the random scission reaction. The simulations were initiated from structures that were taken from previously equilibrated snapshots of the amorphous polymer and of a free-standing thin film. Isolated chains were also used for comparison. Our systems were coupled to a thermal heat bath, and the effect of different coupling constants was studied. Rate of random scission increases as the strength of the temperature coupling increases. Rates of reaction are almost similar in thin films and the bulk, whereas the rates are much faster in isolated chains. Expansion of the free-standing thin film accompanies degradation, producing fragments of various sizes. Chains of higher molecular weights than the initial chains can be produced due to recombination of fragments during the expansion of thin films. The polydispersity index of the resulting fragments is higher in thin films compared to the bulk. The bonds at the low density portion of the thin films have a higher probability of being broken.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"11 2","pages":"Pages 155-166"},"PeriodicalIF":0.0,"publicationDate":"2001-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00078-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79786739","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 15

Spanning-tree models for Af homopolymerizations with intramolecular reactions 分子内均聚反应的生成树模型

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00088-4

C. Sarmoria , D.R. Miller

{"title":"Spanning-tree models for Af homopolymerizations with intramolecular reactions","authors":"C. Sarmoria , D.R. Miller","doi":"10.1016/S1089-3156(99)00088-4","DOIUrl":"10.1016/S1089-3156(99)00088-4","url":null,"abstract":"<div><p>The spanning-tree approximation model is one of the models used for polymerizations with intramolecular reaction regardless of the size of the ring formed. We present a modification of this model that uses more accurate internal estimates of the probabilities of intramolecular reaction. This requires limited Monte Carlo simulations of some molecular structures, resulting in a hybrid probability model (a combined analytic and Monte Carlo model). We then extend the spanning-tree model so that it may be used in the post-gel region. We show three possible extensions of varying degrees of complexity. The resulting models for stepwise A<sub>f</sub> homopolymerizations have been coded into programs that run on desktop PCs in a few seconds. The models calculate the amount of intramolecular conversion, the weight-average molecular weight, the gel point, the weight fraction of soluble material, and the weight-average molecular weight of the sol fraction. We discuss the relative merits of the modified spanning-tree model and its three post-gel extensions and show sample calculations for arbitrary homopolymerization systems.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"11 2","pages":"Pages 113-127"},"PeriodicalIF":0.0,"publicationDate":"2001-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00088-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73902058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 18

The role of adsorption of aniline trimers on the corrosion inhibition process: a ZINDO/1 study 苯胺三聚体在缓蚀过程中的吸附作用:ZINDO/1研究

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00092-6

L.T. Sein Jr. , Yen Wei , S.A. Jansen

引用次数: 34

Conformational statistics of macromolecules using generalized convolution 利用广义卷积的大分子构象统计

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00086-0

G.S. Chirikjian

{"title":"Conformational statistics of macromolecules using generalized convolution","authors":"G.S. Chirikjian","doi":"10.1016/S1089-3156(99)00086-0","DOIUrl":"10.1016/S1089-3156(99)00086-0","url":null,"abstract":"<div><p><span>A new technique for generating statistical properties of chain-molecule conformations is presented. Conditional probability density functions (PDFs) describing the frequency of occurrence of the relative position and orientation of frames of reference affixed to selected backbone atoms serve as the inputs. Ensemble statistical properties of whole chains are generated by performing multiple generalized convolutions of these conditional PDFs. The formulation is shown to include classical theories such as the hindered and freely rotating chains, the Gaussian random walk, and the rotational isomeric state model. The convolution model is modified to include the long-range effects of excluded volume. An analytical example is used to illustrate the procedure. A general algorithm to calculate the ensemble properties of an arbitrary chain macromolecule is presented. In this algorithm, each of the </span><em>N</em> degrees of freedom (e.g. torsion angles) is assumed to have <em>K</em> discrete states. Using the convolution procedure, a chain is divided into <em>P</em> statistical units. The computational requirement is reduced from an <span><math><mtext>O</mtext></math></span>(<em>K</em><sup><em>N</em></sup>) calculation (corresponding to direct enumeration) to one which is <span><math><mtext>O</mtext><mtext>(P(C+K</mtext><msup><mi></mi><mn>N/P</mn></msup><mtext>))</mtext></math></span> where <em>C</em><span> is the computational complexity of the convolution procedure. In the case of a homopolymer, computations are reduced further to </span><span><math><mtext>O</mtext><mtext>(C</mtext><mspace></mspace><mtext>log</mtext><mtext>(P)+K</mtext><msup><mi></mi><mn>N/P</mn></msup><mtext>).</mtext></math></span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"11 2","pages":"Pages 143-153"},"PeriodicalIF":0.0,"publicationDate":"2001-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00086-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82598989","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 21

Hydrogen abstraction from poly(propylene) and poly(propylene oxide) by hydroxyl radicals: a computational quantum semi-empirical study 羟基自由基从聚(丙烯)和聚(环氧丙烷)中提取氢:计算量子半经验研究

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00090-2

F. Posada , P. Malfreyt , J.-L. Gardette

引用次数: 5

A Monte Carlo simulation of grafted poly(ethylene oxide) chains 接枝聚环氧乙烷链的蒙特卡罗模拟

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00085-9

Tonglei Li, Kinam Park

{"title":"A Monte Carlo simulation of grafted poly(ethylene oxide) chains","authors":"Tonglei Li, Kinam Park","doi":"10.1016/S1089-3156(99)00085-9","DOIUrl":"10.1016/S1089-3156(99)00085-9","url":null,"abstract":"<div><p>Conformational changes of a simplified model of grafted poly(ethylene oxide) (PEO) chains were simulated using an off-lattice Monte Carlo model. A random-walk scheme was used in our simulations. The initial polymer structure<span> was modeled with molecular mechanics and models of grafted polymer chains were built using programs developed in our laboratory. During the simulation, all bond angles<span> and bond lengths were kept fixed while the dihedral angles of backbones were changed to search for energy-favorite conformations. Torsional energy, van der Waals interaction, and Coulombic interaction were considered. Periodic boundary conditions were implemented. In addition, the solvent quality was simulated implicitly by modifying the Lennard-Jones 12–6 van der Waals expression. Each PEO chain, 50-monomer long, was represented with a united-atom model. Eight series of simulations with varying solvent quality, simulation temperature, and Coulombic interaction were carried out. For each series, nine different initial grafting densities of grafted PEO chains were considered. Five different conformations were simulated at each grafting density. The calculated system energies, scaling properties, and atom density profiles were studied. Changes in solvent quality produced different structural behaviors. As the grafting density increased, there was a mushroom-to-brush transition, and the scaling property of average layer thickness was dependent on the grafting density.</span></span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"11 2","pages":"Pages 133-142"},"PeriodicalIF":0.0,"publicationDate":"2001-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00085-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83510609","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6

The dimensions of a polymer chain at the coil-to-globule transition 聚合物链在线圈到球体转变时的尺寸

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00087-2

P Romiszowski, A Sikorski

引用次数: 5

Hydrogen abstraction from copolymers of fluorinated olefins and allyl or vinyl ethers by hydroxyl radicals: a computational quantum semi-empirical study 羟基自由基从氟化烯烃和烯丙基或乙烯基醚共聚物中提取氢:计算量子半经验研究

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00091-4

F. Posada , P. Malfreyt , J.-L. Gardette

引用次数: 3

Photoinitiated bulk polymerization of furfuryl methacrylate. Stochastic simulation results using the new model CORUB 甲基丙烯酸糠酰光引发体聚合。采用新模型CORUB的随机仿真结果

Computational and Theoretical Polymer Science Pub Date : 2001-04-01 DOI: 10.1016/S1089-3156(99)00093-8

J.A. Corzo E , N. Davidenko , R. Alvarez

{"title":"Photoinitiated bulk polymerization of furfuryl methacrylate. Stochastic simulation results using the new model CORUB","authors":"J.A. Corzo E , N. Davidenko , R. Alvarez","doi":"10.1016/S1089-3156(99)00093-8","DOIUrl":"10.1016/S1089-3156(99)00093-8","url":null,"abstract":"<div><p>A new stochastic model named CORUB has been used to do a phenomenological description of the photopolymerization<span> of furfuryl methacrylate<span>, with the following methodology. Statistical analysis of the model's adequacy shows a good correlation between experimental data and those modelled stochastically. This model was developed using two stochastic variables that represent the random nature of the intermolecular encounters upon which the Collision Theory is sustained. The amounts of random numbers generated simulate time in a new way, based on the standard physical concept, with satisfactory results. Also, calculating the number of times that each individual step of the reaction mechanism takes place, a new possibility for carrying out the sensitivity analysis is presented. In addition to which, the analogy assumed between the frequency of the random number generated and the effective intermolecular collision allows us to model, exclusively and accurately enough, the effect of temperature as well as to estimate the apparent activation energy precisely. The algorithm of CORUB model was coded in Turbo Pascal 6.0, resulting in the CHEMOD-X program, which constitutes a software specifically elaborated as an integrative part of this work, allowing the model to be used.</span></span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"11 2","pages":"Pages 89-94"},"PeriodicalIF":0.0,"publicationDate":"2001-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00093-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88724234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

Group contribution analysis applied to the Havriliak–Negami model for polyurethanes 群贡献分析应用于聚氨酯Havriliak-Negami模型

Computational and Theoretical Polymer Science Pub Date : 2001-01-01 DOI: 10.1016/S1089-3156(99)00072-0

W.M Davis , J.P Szabo

引用次数: 4