Performance of SuSi: a method for generating atomistic models of amorphous polymers based on a random search of energy minima

The performance of a recently developed method to generate representative atomistic models of amorphous polymers has been investigated. This method, which is denoted SuSi, can be defined as a random generator of energy minima. The effects produced by different parameters used to define the size of the system and the characteristics of the generation algorithm have been examined. Calculations have been performed on poly(L,D-lactic) acid (rho = 1.25 g/cm3) and nylon 6 (rho = 1.084 g/cm(3)), which are important commercial polymers.     

Theoretical strategy to provide atomistic models of comblike polymers: a generation algorithm combined with configurational bias Monte Carlo

A computational strategy to model the amorphous phase of comblike polymers is presented. The strategy, denoted SuSi/CB (CB-configurational bias), combines the strength of an algorithm recently developed to generate reliable microstructures of dense amorphous polymers, which is based on a random search of energy minima, and configurational bias Monte Carlo method. The influence of different parameters used to define the characteristics of SuSi/CB on both the reliability of the generated structures and the computational effort has been examined in detail. Finally, we have modeled and characterized the supramolecular organization of poly(octadecyl acrylate) in the amorphous state.     

Modeling the amorphous phase of comb‐like polymers

In this work, we apply a methodology recently developed by us to perform atomistic simulations of the amorphous phase of poly(α‐octadecyl β‐aspartate) and poly‐ (octadecyl acrylate). The simulation method, which is denoted SuSi/CB, combines the strength of an algorithm specially designed to generate atomistic models of dense amorphous polymers and the Configurational Bias Monte Carlo procedure. Modeling results reveal that poly(octadecyl acrylate) presents a tendency to adopt backbone helical conformations, while no trace of helicity was detected in the amorphous phase poly(α‐octadecyl β‐aspartate). Regarding the side chain organization, the paraffinic pool formed by the octadecyl side chains is slightly greater for the poly(acrylate) than for the poly(β‐aspartate). According to these features, it can be concluded that the small chemical differences between the two investigated polymers are enough to provide some distinctive structural features. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 953–966, 2006     

氢键型超分子聚合物的合成、结构与应用

氢键型超分子聚合物是重复单元经氢键相互作用连接在一起的阵列,可生成液晶态,多样化的几何形状和高有序的凝聚态结构。氢键的温度敏感性和可逆性导致氢键型超分子聚合物具有和传统共价键结合的聚合物不同的性能。氢键型超分子聚合物是一类动态的智能型功能高分子材料,可在光化学、光电转换、非线性光学、弹性体、水凝胶和生物医用工程等领域广泛应用。本文从氢键型超分子聚合物化学(合成与机理)、物理(结构与性能)和工程(加工与应用)三个方面介绍氢键型超分子聚合物的进展。     

Supramolecular polymers fabricated by orthogonal self-assembly based on multiple hydrogen bonding and macrocyclic host–guest interactions

Supramolecular polymers constructed by orthogonal self-assembly based on multiple hydrogen bonding and macrocyclic host-guest interactions have received increasing attention due to their elegant structures,outstanding properties,and potential applications.Hydrogen bonding endows these supramolecular polymers with good adaptability and reversibility,while macrocyclic host-guest interactions give them good selectivity and versatile stimuli-responsiveness.Therefore,functional supramolecular polymers fabricated by these two highly specific,noninterfering interactions in an orthogonal way have shown wide applications in the fields of molecular machines,electronics,soft materials,etc.In this review,we discuss the recent advances of functional supramolecular polymers fabricated by orthogonal self-assembly based on multiple hydroge n bonding and host-guest interactions.In particular,we focus on crown ether-and pillar[n]arene-based supramolecular polymers due to their compatibility with multiple hydrogen bonds in organic solution.The fabrication strategies,interesting properties,and potential applications of these advanced supramolecular materials are mainly concerned.     

Supramolecular Self-assembly Behaviors of Asymmetric Diblock Copolymer Blends with Hydrogen Bonding Interactions between Shorter Blocks Modelled by Yukawa Potentials

We employed the extended self-consistent field theory to investigate the supramolecular self-assembly behaviors of asymmetric diblock copolymer blends (AB/B'C) with hydrogen bonding interactions between shorter B and B'blocks.The hydrogen bonding interactions are described by Yukawa potentials,where the hydrogen bonding donors and acceptors were modelled as two blocks smeared with opposite screened charges.The hierarchical microstructures with parallelly packed lamellae-in-lamellae (Lam) and 4.8.8 Archimedean tilting pattern(4.8.8) were observed at lower and higher hydrogen bonding density (θ),respectively.The hierarchy of Lam and 4.8.8 were demonstrated by the one-and two-dimensional density profiles and the underlying order of the large-length-scale and small-length-scale microstructures were also clarified.It was found that the 4.8.8 is favorable to the stronger hydrogen bonding density or interactions.As θ increases,the microphase transition from Lam to 4.8.8 occurs at θ=0.34,which is mainly attributed to the optimization of the electrostatic energy and conformational entropy with sacrificing the interfacial energy.This work can provide a new strategy to understand the supramolecular self-assembly as well as the mechanism behind the formation of complex hierarchical microstructures.     

Coarse-graining: a procedure to generate equilibrated and relaxed models of amorphous polymers

We present a coarse-graining procedure to construct models of amorphous polymers. The method, which was applied to polyethylene, is based on a generation-relaxation strategy previously developed to provide independent atomistic microstructures. The coarse-graining was performed by assigning positions to mesoscopic particles denoted blobs, which represent groups of atoms, through distance, angle and dihedral distribution functions. The interaction energy between pairs of blobs was evaluated through a soft potential, whose parameters were derived from atomistic models. Three levels of coarse-graining that differ in the number of atoms included in the blob have been considered. The structural and energy-related properties calculated using the coarse-grained models developed in this study are in good agreement with those obtained using atomistic simulations.     

Application of the sCPA equation of state for polymer solutions

Specific interactions, for example hydrogen bonding, dominate in numerous industrially important polymeric systems, both polymer solutions and blends. Typical cases are water-soluble polymers including biopolymers of special interest to biotechnology (e.g. the system polyethyleneglycol/dextran/water). Furthermore, most polymer blends are non-compatible and the requirement for compatible polymer pairs is often the presence of hydrogen-bonding interactions (e.g. polyvinylchloride/chlorinated polyethylene). In this work we give at first a short, comparative evaluation of existing thermodynamic models suitable for polymeric systems that take into account, explicitly, specific interactions like HB. The range of application of the models in terms of phase equilibria and their specific characteristics (accuracy of calculation, degree of complexity) are discussed. Finally, vapor–liquid equilibria (VLE) calculations for a number of polymer+solvent systems (including five different polymers) with a novel and very promising model are presented. This model is in the form of an equation of state that is (in its general formulation) non-cubic with respect to volume and has separate terms for physical and chemical interactions. The model has recently been proposed and has already been successfully applied to non-polymeric hydrogen-bonding systems (alcohol/water/hydrocarbons). This is the first time that it is extended to polymer solutions.     

Coarse-grained representation of beta-helical protein building blocks

A general strategy to develop coarse-grained models of beta-helical protein fragments is presented. The procedure has been applied to a building block formed by a two-turn repeat motif from E. coli galactoside acetyltransferase, which is able to provide a very stable self-assembled tubular nanoconstruct upon stacking of its replicas. For this purpose, first, we have developed a computational scheme to sample very efficiently the configurational space of the building block. This method, which is inspired by a strategy recently designed to study amorphous polymers and by an advanced Monte Carlo algorithm, provides a large ensemble of uncorrelated configurations at a very reasonable computational cost. The atomistic configurations provided by this method have been used to obtain a coarse-grained model that describes the amino acids with fewer particles than those required for full atomistic detail, i.e., two, three, or four depending on the chemical nature of the amino acid. Coarse-grained potentials have been developed considering the following types of interactions: (i) electrostatic and van der Waals interactions between residues i and i + n with n >/= 2; (ii) interactions between residues i and i + 1; and (c) intra-residue interactions. The reliability of the proposed model has been tested by comparing the atomistic and coarse-grained energies calculated for a large number of independent configurations of the beta-helical building block.     

Routes to Hydrogen Bonding Chain‐End Functionalized Polymers

The contribution of supramolecular chemistry to polymer science opens new perspectives for the design of polymer materials exhibiting valuable properties and easier processability due to the dynamic nature of non‐covalent interactions. Hydrogen bonding polymers can be used as supramolecular units for yielding larger assemblies that possess attractive features, arising from the combination of polymer properties and the responsiveness of hydrogen bonds. The post‐polymerization modification of reactive end‐groups is the most common procedure for generating such polymers. Examples of polymerizations mediated by hydrogen bonding‐functionalized precursors have also recently been reported. This contribution reviews the current synthetic routes toward hydrogen bonding sticker chain‐end functionalized polymers.     

Hydrogen-Bond Structure and Low-Frequency Dynamics of Electrolyte Solutions: Hydration Numbers from ab Initio Water Reorientation Dynamics and Dielectric Relaxation Spectroscopy

We present an atomistic simulation scheme for the determination of the hydration number (h) of aqueous electrolyte solutions based on the calculation of the water dipole reorientation dynamics. In this methodology, the time evolution of an aqueous electrolyte solution generated from ab initio molecular dynamics simulations is used to compute the reorientation time of different water subpopulations. The value of h is determined by considering whether the reorientation time of the water subpopulations is retarded with respect to bulk-like behavior. The application of this computational protocol to magnesium chloride (MgCl₂) solutions at different concentrations (0.6–2.8 mol kg⁻¹) gives h values in excellent agreement with experimental hydration numbers obtained using GHz-to-THz dielectric relaxation spectroscopy. This methodology is attractive because it is based on a well-defined criterion for the definition of hydration number and provides a link with the molecular-level processes responsible for affecting bulk solution behavior. Analysis of the ab initio molecular dynamics trajectories using radial distribution functions, hydrogen bonding statistics, vibrational density of states, water-water hydrogen bonding lifetimes, and water dipole reorientation reveals that MgCl₂ has a considerable influence on the hydrogen bond network compared with bulk water. These effects have been assigned to the specific strong Mg-water interaction rather than the Cl-water interaction.     

Increased alignment of electronic polymers in liquid crystals via hydrogen bonding extension

Crucial for the development of enhanced electrooptic materials is the construction of highly anisotropic materials. Nematic liquid crystals are able to control the chain conformation and alignment of poly(phenylene ethynylene)s (PPEs), producing electronic polymers with chain-extended planar conformations for improved transport properties. Here, we show that the dichroic ratio, and hence polymer alignment, increases dramatically when interpolymer interactions are introduced by end capping the PPE with hydrogen bonding groups. This increased order can be readily turned off by the introduction of a competing monofunctionalized hydrogen bonding compound. The formation of hydrogen bonds between the polymers results in the formation of gels and elastomers which may be of interest for future applications.     

Particle and breath figure formation of triblock copolymers having self‐complementary hydrogen‐bonding units

Novel triblock copolymers having self‐complementary hydrogen‐bonding units were synthesized by using reversible addition–fragmentation transfer polymerization. As characterized by dynamic light scattering and atomic force microscopy, these polymers formed noncovalently crosslinked polymer particles and showed an aggregation behavior by intermolecular and intramolecular interactions. At low concentration, polymers formed nanoparticles, and the particle diameter increased with increasing polymer concentration. Well‐ordered hexagonal microstructures were prepared by “Breath Figure” technique with the triblock copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Computational tool to model the packing of polycyclic chains: structural analysis of amorphous polythiophene

A very efficient computational procedure, which was previously developed to generate and relax atomistic models of linear and comb-like amorphous polymers, has been adapted to model the amorphous phase of polycyclic systems. The strategy, which is a based in a generation algorithm that eliminates the torsion strain and a simple Monte Carlo Metropolis method to relax the generated structures, has been used to predict the density of amorphous polythiophene by combining NVT and NPT simulations. The theoretical value is in the excellent agreement with the experimental one, the former being overestimated by only 3-5%. Next, the molecular conformation and the packing of the rings were studied in detail. Interestingly, the amorphous phase of polythiophene can be described as a packing of elongated molecular chains more or less aligned in the same direction, in which the thiophene rings close in the space but belonging to different chains tend to adopt approximate parallel or antiparallel displaced pi-stacked arrangements.     

From mesoscale back to atomistic models: a fast reverse-mapping procedure for vinyl polymer chains

This paper introduces a systematic procedure to obtain well-relaxed atomistic melt structures from mesocale models of vinyl polymers based on sequences of diads. Following the methodology introduced by Milano and Müller-Plathe [J. Phys. Chem. B. 2005, 109, 18609], coarse-grain models consisting of sequences of superatoms of two different types meso and racemo have been used to relax mesocale melts of atactic and syndiotactic polystyrene. The proposed method, based on a fully geometrical approach, does not involve expensive potential energy and force evaluations and allows a very fast and efficient reconstruction of the atomistic detail. The method, successfully tested against experimental data, allows us to obtain all atom models of both stereoregular and stereoirregular polymers and opens the possibility of relaxing large molecular weight melts of vinyl chains.     

Supramolecular polymers: from scientific curiosity to technological reality

Supramolecular polymers^[1] are introduced as a new approach to come to materials in which the repeating units are not connected by covalent bonds but by specific secondary interactions. Self-complementary quadruple hydrogen bonded structures with high association constants are presented as easy to synthesize fragments in supramolecular polymers. Some of the many possibilities of equilibrium polymers are discussed, while it is shown that these supramolecular polymers can obtain materials properties normally only obtained with macromolecules.     

Self-organized nanostructures of poly(4-vinylpyridine), polyaniline and polyamides due to metal complexation

Comb-shaped supramolecules are constructed using flexible polymers and semi-rigid conjugated undoped or doped conjugated polymers upon complexing Zinc dodecyl benzene sulphonate, Zn(DBS)₂. Selforganized nanostructures are formed in the bulk due to competing attractive interactions (coordination or water mediated hydrogen bonding) and repulsive polar/nonpolar interactions, showing characteristic long periods of ca. 30 Å.     

氢键识别超分子聚合物的新进展

近年来,由于氢键作用对聚合物的热力学性质、微观自组装、结晶及液晶行为的重要影响,氢键识别在超分子聚合物的分子设计与结构控制方面的应用受到广泛关注。本文系统介绍了氢键识别体系的类型与性质,以及分子结构、分子内氢键对氢键识别强度的影响,讨论了羧酸与吡啶间氢键识别体系、与核苷相关的氢键识别体系以及四重氢键识别体系在超分子聚合物中的最新应用,主要介绍了氢键识别超分子聚合物的合成、结构、性质及功能。     

Molecular dynamics simulations of heptyl phosphonic acid: a potential polymer component for fuel cell polymer membrane

Atomistic molecular dynamics simulations have been performed on heptyl phosphonic acid (HPA) to understand the dynamic hydrogen bonding network in the liquid phase. HPA is a phosphonic-acid functionalized alkane (heptane) and a model compound for one of the promising polymers for high temperature (>100 degrees C) fuel cell polymer electrolyte membranes. For the simulation, a force field for this molecule has been generated with the help of quantum chemical calculations and optimized by simplex algorithm. The force field has been validated against experimentally measured properties, for example, density and self-diffusion constant. From molecular dynamics simulations conducted at different temperatures, we have confirmed the hypothesis of dynamic hydrogen bond network formation in this material.