Computational and Theoretical Polymer Science最新文献

{"title":"The atomistic simulation of the gas permeability of poly(organophosphazenes). Part 1. Poly(dibutoxyphosphazenes)","authors":"J.R. Fried,&nbsp;P. Ren","doi":"10.1016/S1089-3156(00)00005-2","DOIUrl":"10.1016/S1089-3156(00)00005-2","url":null,"abstract":"<div><p>Self-diffusion and solubility coefficients of six gas molecules (He, Ne, O₂, N₂, CH₄, and CO₂) in two poly(dibutoxyphosphazenes)—poly[bis(<em>n</em>-butoxy)phosphazene] (PnBuP) and poly[bis(<em>sec</em><span><span>-butoxy)phosphazene] (PsBuP)—have been investigated by means of molecular simulation using the </span>COMPASS<span> molecular mechanics force field. Diffusion coefficients were obtained from molecular dynamics (NVT ensemble) using up to 3</span></span> <span><span>ns simulation time. Solubility coefficients were obtained by means of a Grand Canonical Monte Carlo<span><span> (GCMC) method. Results of both simulations were in generally good agreement with experimental data with the exception of the simulation results for gas solubility in PsBuP where differences from the data may be attributed to </span>microcrystallinity of the experimental sample. In the case of diffusivity, diffusion coefficients correlated well with the square of the effective diameter of the diffusing gas. Similarly a good correlation was found between the solubility coefficients obtained by GCMC simulation of </span></span>sorption isotherms and the Lennard-Jones potential well depth parameter, </span><em>ϵ</em>/<em>k</em>.</p><p>The transition-state model of Gusev and Suter was used to determine free volume and free volume distribution for PnBuP, PsBuP, and poly[bis(<em>iso</em>-butoxy)phosphazene] (PiBuP). The diffusion coefficient for a given gas in each polyphosphazene was found to correlate exponentially with its accessible free volume fraction. A model for the distribution of accessible free volume, derived from the Cohen–Turnbull theory for the self diffusion of a liquid of hard spheres, was found to provide excellent fit with the simulation results.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 5","pages":"Pages 447-463"},"PeriodicalIF":0.0,"publicationDate":"2000-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(00)00005-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78234809","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}

{"title":"Molecular simulation of small molecule diffusion and solution in dense amorphous polysiloxanes and polyimides","authors":"D. Hofmann,&nbsp;L. Fritz,&nbsp;J. Ulbrich,&nbsp;D. Paul","doi":"10.1016/S1089-3156(00)00007-6","DOIUrl":"10.1016/S1089-3156(00)00007-6","url":null,"abstract":"<div><p><span>Results of extensive molecular modeling investigations on the transport of different small molecules in flexible chain rubbery polysiloxanes and stiff chain glassy </span>polyimides<span> are discussed. Extended equilibration procedures were necessary to obtain reasonable packing models for the polyimides. The transition state Gusev–Suter Monte Carlo method<span> was utilised to prove a reasonable coincidence between simulated and measured diffusivity and solubility values for the model structures. A comparison between the static structure and the dynamic behaviour of the free volume in the simulated flexible chain rubbery polymers and stiff chain glassy polymers reveals qualitative differences which are decisive for experimentally observable differences in the diffusion of small molecules in these materials.</span></span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 5","pages":"Pages 419-436"},"PeriodicalIF":0.0,"publicationDate":"2000-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(00)00007-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81995116","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}

{"title":"Molecular dynamics simulation of the PEO sulfonic acid anion in water","authors":"J. Ennari,&nbsp;I. Neelov,&nbsp;F. Sundholm","doi":"10.1016/S1089-3156(00)00006-4","DOIUrl":"10.1016/S1089-3156(00)00006-4","url":null,"abstract":"<div><p><span><span>Atomistic molecular modeling has been used to study the sulfonic acid anion of poly(ethylene oxide) (PEO sulfonic acid anion) in vacuum and a </span>polymer electrolyte<span> system consisting of the PEO sulfonic acid anion in water. The vibrational spectra of the molecules were simulated by the local mode method and found to be in good agreement with the experimental IR and Raman spectra. The structure of PEO sulfonic acid anion was studied in vacuum and water and compared to the structure of an isolated PEO sulfonic acid in vacuum. The simulated value for the root mean square end-to-end distance for the PEO sulfonic acid anion was 22</span></span> <!-->Å in vacuum and 12<!--> <span>Å in water. The root mean square radius of gyration of the PEO sulfonic acid anion was 8.4</span> <!-->Å in vacuum and 5.6<!--> <!-->Å in water. The PEO sulfonic acid anion was randomly coiled in water and in an extended shape in vacuum.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 5","pages":"Pages 403-410"},"PeriodicalIF":0.0,"publicationDate":"2000-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(00)00006-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89783137","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}

{"title":"Translational diffusion in Monte Carlo simulations of polymer melts: center of mass displacement vs. integrated velocity autocorrelation function","authors":"R. Ozisik ,&nbsp;P. Doruker ,&nbsp;W.L. Mattice ,&nbsp;E.D. von Meerwall","doi":"10.1016/S1089-3156(00)00008-8","DOIUrl":"10.1016/S1089-3156(00)00008-8","url":null,"abstract":"<div><p>Translational diffusion has been simulated in monodisperse melts of four linear alkanes, C_2<em>x</em>H_{4<em>x</em>+2}, <em>x</em>=6,30,50,158, and two cyclic alkanes, C_2<em>x</em>H_4<em>x</em>, <em>x</em>=30,50, at 473<!--> <!-->K. The alkanes are expressed in a coarse-grained representation using <em>x</em><span><span> beads on a high coordination lattice, one bead for every two carbon atoms. Short-range intramolecular interactions are controlled by an adaptation of the rotational isomeric state model for unperturbed polyethylene<span>, and the long-range interactions are controlled by a step-wise three-shell potential energy function derived from a continuous Lennard-Jones potential energy function. Acceptance of trial moves, each of which changes the coordinates of a single bead only, is governed by the Metropolis rule. Translational </span></span>diffusion coefficients, </span><em>D</em><span>, are estimated from the mean square displacement of the center of mass and the integral of the velocity autocorrelation function. Both approaches yield the same value for </span><em>D</em><span>, which demonstrates that the velocity has been defined in a reasonable manner in the Monte Carlo simulation. A method is proposed for the estimation of </span><em>D</em> when the trajectory is not quite long enough to have achieved the behavior characteristic of the limit as time approaches infinity.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 5","pages":"Pages 411-418"},"PeriodicalIF":0.0,"publicationDate":"2000-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(00)00008-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84750210","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}

{"title":"Processes of drug transfer with three different polymeric systems with transdermal drug delivery","authors":"E.M. Ouriemchi,&nbsp;J.M. Vergnaud","doi":"10.1016/S1089-3156(00)00003-9","DOIUrl":"10.1016/S1089-3156(00)00003-9","url":null,"abstract":"<div><p>The transdermal<span> drug delivery exhibits two main advantages over the conventional oral delivery, by-passing the hepatic first-pass, and maintaining the plasma drug level at a plateau over a long period of time. The role of the transdermal therapeutic systems is to apply a constant drug concentration on the skin for a long time, while the skin acts as a membrane. Thus the drug transfer through the skin reaches a constant rate under stationary conditions after a short time under transient conditions. Three transdermal therapeutic systems are considered: a monolithic device made of a polymer containing the drug; this monolithic device in contact with a drug reservoir; a porous polymer containing the drug. The monolithic device can maintain a constant drug delivery only when the diffusivity of the drug through this polymer is very high. In association with a reservoir, this device becomes more efficient. The system made of a porous polymer with convective transfer of the drug appears to be more effective, providing a constant drug concentration on the skin surface, which is responsible for a constant rate of drug transfer through the skin and a constant plasma drug level over a long period of time.</span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 5","pages":"Pages 391-401"},"PeriodicalIF":0.0,"publicationDate":"2000-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(00)00003-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84250477","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}

{"title":"Effect of the nature of the polymer and of the process of drug release (diffusion or erosion) for oral dosage forms","authors":"A Aı̈naoui,&nbsp;J.M Vergnaud","doi":"10.1016/S1089-3156(00)00004-0","DOIUrl":"10.1016/S1089-3156(00)00004-0","url":null,"abstract":"<div><p>Conventional oral dosage forms with immediate release are associated with plasma drug levels alternating between high peaks and low troughs leading to harmful side effects. These side effects are reduced and the therapy is optimized by using oral dosage forms with controlled release. Usually these dosage forms consist of devices where the drug is dispersed through a biocompatible polymer, which plays the role of a matrix, and the polymer plays the major role for controlling the drug release along the gastrointestinal tract. Depending on the nature of the polymer, the process of drug release is different and the two extreme cases are considered: the one with stable polymers where the drug release is controlled by diffusion with the more simple case of constant diffusivity; the other with erodible polymers with a constant rate of erosion. As the gastrointestinal transit time is finite, the radius of spherical dosage forms is evaluated such that the time of drug delivery is 24<!--> <!-->h. Various shapes are also considered with the same polymer and the same diffusivity or rate of erosion, by keeping the same volume and mass of drug for these dosage forms. Following these studies, the plasma drug level is also assessed for these two types of dosage forms. Some results of interest are obtained: for each type of polymer, the shape given to the dosage form exhibits some interest for the kinetics of drug release; the type of polymer is of prime importance, and erodible polymers are associated with a more constant plasma drug level. Thus these results take stock of the question of drug release by considering the properties of the polymer, whether it is stable with its diffusivity or it is erodible with its rate of erosion. Finally this knowledge makes possible the evaluation of the dimensions of dosage forms necessary for a given time of drug delivery and a given therapy.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 5","pages":"Pages 383-390"},"PeriodicalIF":0.0,"publicationDate":"2000-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(00)00004-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84074459","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}

{"title":"Intramolecular and intermolecular association in thermoreversible gelation of hydrophobically modified associating polymers","authors":"F. Tanaka,&nbsp;T. Koga","doi":"10.1016/S1089-3156(99)00048-3","DOIUrl":"10.1016/S1089-3156(99)00048-3","url":null,"abstract":"<div><p><span>In the thermoreversible gelation<span> of hydrophobically modified water-soluble associating polymers, intramolecular association competes with intermolecular association. The former leads to intramolecular </span></span>micelles<span> with hydrophobic cores decorated by loops of hydrophilic chains. Loop formation prevents an intermolecular cross-linking. This paper theoretically details the effect of small loops on the sol/gel transition with multiple cross-link junctions in associating polymer solutions. In the case of telechelic associating polymers, the problem is shown to be mathematically equivalent to the mixture of monofunctional and bifunctional polymers. The gelation concentration changes with a parameter describing the probability of a single loop formation. Relative populations of the six fundamental chain categories are derived as a function of the total polymer concentration with special attention to the formation of flower micelles. For polymers carrying many hydrophobes, Monte Carlo computer simulation is carried out by using model chains to see how intramolecular micellization competes with intermolecular cross-linking.</span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 259-267"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00048-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73145551","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}

{"title":"Monte Carlo analysis of the osmotic pressure of athermal polymer solutions in dilute and semi-dilute regimes","authors":"K. Shida ,&nbsp;K. Ohno ,&nbsp;M. Kimura ,&nbsp;Y. Kawazoe","doi":"10.1016/S1089-3156(99)00050-1","DOIUrl":"10.1016/S1089-3156(99)00050-1","url":null,"abstract":"<div><p><span>The enrichment Monte Carlo algorithm is applied here, for the first time, to calculate the osmotic pressure of an athermal solution of linear chains on a lattice, in dilute and semi-dilute regimes. Complementarily to the Widom's test particle insertion method, the algorithm enables one to estimate directly the free energy and the osmotic pressure of the solution. The result shows that there is a large deviation in the free energy from the Flory–Huggins theory which may be attributed to the chain internal entropy. Moreover, the osmotic pressure shows des Cloizeaux's </span><em>c</em>^9/4 behavior clearly when the concentration, <em>c</em><span>, is greater than the estimated overlap concentration. We estimate also the second and third virial coefficients that are compared with experimental values.</span></p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 281-285"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00050-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90846616","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}

{"title":"Computer simulation of structural changes in the ferroelectric phase transition of vinylidene fluoride–trifluoroethylene copolymers","authors":"Y. Abe ,&nbsp;K. Tashiro ,&nbsp;M. Kobayashi","doi":"10.1016/S1089-3156(99)00042-2","DOIUrl":"10.1016/S1089-3156(99)00042-2","url":null,"abstract":"<div><p><span>Structural change in the ferroelectric<span><span> phase transition of vinylidene fluoride (VDF)–trifluoroethylene </span>copolymers<span> has been simulated by using molecular dynamics (MD) technique. The force field parameters used in this simulation were those determined in the previous paper [Tashiro et al., Ferroelectrics 1995;171:281] but with some modifications to reproduce the molecular and crystal structures and the infrared/Raman spectra of PVDF crystal forms I, II, and III to a higher degree. The MD calculation was made for the crystal structures of VDF 50 and 70</span></span></span> <span>mol% copolymers, where the MD unit cells consisted of 16–36 chains of different monomer sequences under the three-dimensional periodic boundary condition. In the VDF 50% copolymer case, for example, the </span><em>trans</em>-to-<em>gauche</em> conformational change was found to occur at about 390<!--> <!-->K. The transition temperature estimated for VDF 70% copolymer was about 470<!--> <!-->K, higher than that of VDF 50% copolymer. This indicates that the copolymer with higher VDF content exhibits the transition at higher temperature, consistent with the observed results. The molecular conformation in the high-temperature phase was found to be a statistical combination of <em>TG</em>⁺, <em>TG</em>⁻, <em>T</em>₃<em>G</em>⁺ and <em>T</em>₃<em>G</em>⁻ sequences. The population of <em>TG</em>⁺ and <em>TG</em>⁻ was higher and that of <em>T</em>₃<em>G</em>⁺ and <em>T</em>₃<em>G</em>⁻ was lower for the copolymer with higher VDF content, which was also consistent with the experimental data. The <em>trans</em>–<em>gauche</em> conformational change was done with large thermal rotation of the chains, resulting in the extinction of the electric polarization of the whole unit cell in the high-temperature phase. The ratio of the <em>a</em> and <em>b</em> axes of the basic unit cell was 1.73, characteristic of the hexagonal-type structure of the high-temperature phase.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 323-333"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00042-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74623629","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}

{"title":"Phase separation of liquid crystal–polymer mixtures","authors":"M Motoyama ,&nbsp;H Nakazawa ,&nbsp;T Ohta ,&nbsp;T Fujisawa ,&nbsp;H Nakada ,&nbsp;M Hayashi ,&nbsp;M Aizawa","doi":"10.1016/S1089-3156(99)00044-6","DOIUrl":"10.1016/S1089-3156(99)00044-6","url":null,"abstract":"<div><p>Phase separation in liquid crystal–polymer mixtures is studied by computer simulations in two dimensions. The domain morphology resulting from the phase separation either by temperature quench or by polymerization is investigated by solving the coupled set of equations for the local volume fraction and the nematic order parameter. In a temperature quench, it is found that transient concentric domains are constituted near the nucleation regime of nematic ordering. Phase separation induced by polymerization is modeled by taking into account the time dependence of the molecular weight of polymer chains. Assuming a strong concentration dependence of the mobility, a transient network-like domain of polymer-rich phase is formed. The morphology is compared with the experimental results.</p></div>","PeriodicalId":100309,"journal":{"name":"Computational and Theoretical Polymer Science","volume":"10 3","pages":"Pages 287-297"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S1089-3156(99)00044-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84614262","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}