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Journal ArticleDOI

Monte Carlo Simulations of Chain Dimensions and Conformational Properties of Various Poly(n-alkyl methacrylates) in Solution

28 Oct 2008-Journal of Macromolecular Science, Part B (Taylor & Francis Group)-Vol. 47, Iss: 6, pp 1075-1086
TL;DR: In this article, a series of chemically different poly(n-alkyl methacrylates) including poly(methacrylate), poly(methyl methacricyl side group), poly (n-butyl methyl side group) and poly(poly(nhexyl methyl methacyl) side group were compared with experimentally obtained dimensions in the literature using the Mark-Houwink relationship as well as data available from direct determinations in θ solvents.
Abstract: Rotational Isomeric State (RIS) Metropolis Monte Carlo (RMMC) simulations of the conformational properties and chain dimensions of a series of chemically different poly(n-alkyl methacrylates) including poly(methyl methacrylate), poly(n-butyl methacrylate), poly(n-hexyl methacrylate), and poly(phenyl methacrylate), in the θ state were investigated, and (〈r2〉/M)1/2, (〈s2〉/M)1/2 and C n were calculated and compared in order to obtain fundamental understanding of the influence of the chemical structure. Simulations were conducted for different molecular weights. Results obtained from the simulations are compared with experimentally obtained dimensions in the literature using the Mark-Houwink relationship as well as, in some cases, data available from direct determinations in θ solvents. Good agreement between simulation and experimental data was obtained. The backbone conformation is predominantly trans in these polymers. Increase in bulkiness and rigidity of the substituting acrylate side group results in an...
Citations
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Journal ArticleDOI
TL;DR: In this paper, the grant number: POCI-PPCDT/EQU/60483/2004 was assigned to the Portuguese Ministry of Science and Technology of Portugal and the European Community (FEDER).
Abstract: Fundacao para a Ciencia e a Tecnologia (FCT) Ministry of Science and Technology of Portugal European Community (FEDER); Grant Number: POCI-PPCDT/EQU/60483/2004

16 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined the branch lengths resulting from both backbiting and intermolecular chain transfer to polymer for the solution polymerization of butyl acrylate, using a rate-equation model and ordinary differential equations.
Abstract: Branch lengths resulting from both backbiting and intermolecular chain transfer to polymer are examined for the solution polymerization of butyl acrylate, using a rate-Equation model and ordinary differential equations. Backbiting is allowed to generate branches of varying length, according to a cumulative distribution function obtained from a lattice kinetic Monte Carlo simulation. About 8% of the branches produced by backbiting are 10 mers or longer. In contrast to common assumptions about the origins of short-chain and long-chain branches, the model indicates that nearly all of the long-chain branches may be produced by backbiting, rather than intermolecular chain transfer to polymer.

14 citations

Journal ArticleDOI
TL;DR: In this paper, the authors developed a general methodology for predicting the chain dimensions of any polymer chain in the unperturbed state starting from its detailed atomistic structure, which is based on performing Metropolis Monte Carlo (MC) simulation, leading to equilibration of the conformational distribution of a single unperturbated polymer chain, subject only to local interactions along its backbone.
Abstract: The spatial dimensions and the stiffness (characteristic ratio, C∞) of polymer chains are intimately related to key macroscopic properties such as the plateau modulus and the melt viscosity. Furthermore, these molecular features are very important in the selection and design of copolymer species used in directed self-assembly lithographic processes. We have developed a general methodology for predicting the chain dimensions of any polymer chain in the unperturbed state starting from its detailed atomistic structure. The methodology is based on performing Metropolis Monte Carlo (MC) simulation, leading to equilibration of the conformational distribution of a single unperturbed polymer chain, subject only to local interactions along its backbone. To define what constitutes local interactions, the maximal topological distance of repeat units between which nonbonded forces are active is varied systematically, until a maximum in stiffness is achieved. Our methodology was validated by comparing the predicted ch...

13 citations

Dissertation
01 Dec 2011
TL;DR: In this article, a laboratory rig was designed and built to simulate this environment, producing and measuring representative mist flows, and the contribution of the components of a commercial lubricant to its misting properties was studied.
Abstract: The presence of lubricant mist in the piston assembly of an automotive engine has been known of for many years, but has not been specifically investigated. This study, therefore, focuses on understanding the lubricant misting process and its effect on the engine in terms of lubricant degradation. Informed by existing literature, it was hypothesised that mist is formed in the piston ring gaps. A laboratory rig was designed and built to simulate this environment, producing and measuring representative mist flows. Using this rig, the contribution of the components of a commercial lubricant to its misting properties was studied. Base oil viscosity and molecular weight, and the presence of polymeric viscosity modifiers were identified as being the key parameters controlling the tendency of an oil to form mist. Further investigation using viscosity modifiers of varying size and molecular structure was performed, indicating differences between the behaviour of linear and star polymers. Measurements of the droplet flows in the crankcase of an engine were made using a particle sizer. These confirmed the dependency of misting properties on viscosity, and validated the hypothesis that lubricant mist in the crankcase is formed in the piston assembly by a similar mechanism to that produced in the laboratory rig. Longer engine tests were used to investigate the effect of lubricants with varying misting tendency on lubricant degradation. A range of chemical and rheological analyses were performed to compare fresh and used lubricant samples in different flows and positions in the engine. These tests were not able to differentiate between the degradation of the different lubricants tested, though the degradation of lubricant in different positions in the engine varied significantly. It was shown that lubricant mist is formed in the piston assembly and that lubricant misting is a significant lubricant transport mechanism.

4 citations

Dissertation
05 Apr 2010
TL;DR: In this paper, a combination of stochastic and deterministic models is used to examine two significant mechanistic issues in free radical polymerization, including the zero-one assumption concerning the number of radicals.
Abstract: Polymer chain microstructure, including characteristics such as molecular weight and branch length, can impact the end-use properties of the polymer. The assumptions contained in deterministic models prevent examination of the structure of individual polymer chains, so removal of these assumptions is necessary to gain insight into molecular-level mechanisms that determine chain microstructure. The work presented here uses a combination of stochastic and deterministic models to examine two significant mechanistic issues in free radical polymerization. The zero-one assumption concerning the number of radicals is often made for miniemulsion polymerization using oil-soluble initiators because of accelerated termination due to radical confinement. Although most of the initiator is present inside the particles, opposing viewpoints exist as to whether the locus of radical generation is the particle phase or the aqueous phase. A well-mixed kinetic Monte Carlo (KMC) model is used to simulate the molecular weight distribution and the results are compared to estimated molecular weights for several chain-stopping events, with the finding that the dominant nucleation mechanism varies with reaction temperature and particle size. Intramolecular chain transfer to polymer, or backbiting, is often assumed to produce only short-chain branches. Using a lattice KMC model, a cumulative distribution function (CDF) is obtained for branch lengths produced by backbiting. Implementation of the CDF in both a rate-equation model and the well-mixed KMC model shows that, for the butyl acrylate solution polymerization system used for comparison, backbiting is responsible for most of the branches, including long-chain branches, even though overlap of the polymer coils in the solution is predicted, a condition which would normally be expected to lead to significant intermolecular chain transfer to polymer. The well-mixed KMC model provides a more thorough analysis of chain microstructure while the rate-equation model is more computationally efficient.

4 citations


Cites background from "Monte Carlo Simulations of Chain Di..."

  • ...Chain conformation in various acrylates and methacrylates has been studied using rotational isomeric states-Metropolis Monte Carlo, giving good agreement with experimentally measured values for properties such as radius of gyration [24, 59]....

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References
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Journal ArticleDOI
TL;DR: In this article, a modified Monte Carlo integration over configuration space is used to investigate the properties of a two-dimensional rigid-sphere system with a set of interacting individual molecules, and the results are compared to free volume equations of state and a four-term virial coefficient expansion.
Abstract: A general method, suitable for fast computing machines, for investigating such properties as equations of state for substances consisting of interacting individual molecules is described. The method consists of a modified Monte Carlo integration over configuration space. Results for the two‐dimensional rigid‐sphere system have been obtained on the Los Alamos MANIAC and are presented here. These results are compared to the free volume equation of state and to a four‐term virial coefficient expansion.

35,161 citations


"Monte Carlo Simulations of Chain Di..." refers methods in this paper

  • ...In the RMMC method, the conformational states of the chains were generated using the Metropolis Monte Carlo method.[10] For polymer chains under θ conditions, the interactions between atoms far-separated along the chain effectively vanish....

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Book
01 Jan 1969

4,347 citations

Journal ArticleDOI
TL;DR: In this paper, an all-atom CFF93 force field for polycarbonates based on ab initio calculations is reported, and the force field parameters are derived by fitting to quantum mechanical total energies, first and second derivatives of total energies and electrostatic potentials, all generated from AB initio quantum mechanical calculations on model compounds at HF/6-31GS level of theory.
Abstract: An all-atom CFF93 force field for polycarbonates based on ab initio calculations is reported. Force field parameters are derived by fitting to quantum mechanical total energies, first and second derivatives of total energies, and electrostatic potentials, all generated from ab initio quantum mechanical calculations on model compounds at HF/6-31GS level of theory. Valence parameters and ab initiocharges are then scaled to correct for differences between experiment and the Hartree-Fock approximation. The van der Waals parameters and the scaling factors for atomic partial charges are determined from crystal structures. Based on the force field, molecular mechanics calculations are performed for several model compounds, and the results are compared with experimental values and with the results of the ab initio calculations.

933 citations


"Monte Carlo Simulations of Chain Di..." refers methods in this paper

  • ...Conformational energy calculations about various bond pairs of the repeat units were performed using the polymer-consistent-forcefield (PCFF),[8,9] which is well parameterized to work for polymethacrylates, among many other types of polymers....

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Journal ArticleDOI

137 citations


"Monte Carlo Simulations of Chain Di..." refers background or methods in this paper

  • ...Conformational energy calculations about various bond pairs of the repeat units were performed using the polymer-consistent-forcefield (PCFF),[8,9] which is well parameterized to work for polymethacrylates, among many other types of polymers....

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  • ...According to Flory,[9] if nonbonded interactions are extended to second-order interactions, this is considered the θ state of a polymer chain....

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Journal ArticleDOI
TL;DR: In this paper, the authors calculate l'energie conformationnelle des oligomeres monomere and trimere du PMMA and for les segments figes dans les chaines stereoregulieres, including les formes isotactiques (meso) and syndiotactique (racemique).
Abstract: Calcul de l'energie conformationnelle des oligomeres monomere et trimere du PMMA et pour les segments figes dans les chaines stereoregulieres, incluant les formes isotactiques (meso) et syndiotactique (racemique)

129 citations


"Monte Carlo Simulations of Chain Di..." refers methods in this paper

  • ...These studies include, for example, atactic poly(methyl acrylate)[20,21] using Monte-Carlo chains[21] with a Bernoullian distribution of meso and racemic dyads; atactic poly(cyclohexyl acrylate)[22] with Bernoullian distribution of dyads using Monte Carlo chain generation; atactic poly(phenyl acrylate) and its model compound phenyl ester of 2,4-dimethyl glutaric acid[23,24]; isotactic-PMMA[25,26]; atactic PEMA[27]; and atactic poly(n-alkyl methacrylates) [PMMA, PEMA, and poly(isopropyl methacrylate) having specified meso-racemic dyad ratios]....

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