MCDP: an advanced tool to simulate comb‐like polymers

A strategy to study polymeric systems with ordered structures, and in particular comb‐like polymers, is presented. These are dense systems for which atomistic simulations with conventional methods are difficult or even impracticable. The strategy, which has been incorporated into a computer program named MCDP, is based on a Configuration Bias Monte Carlo algorithm and a method to investigate the structure of crystalline polymers using force‐field calculations. To obtain a maximum efficiency, the MCDP computer program has been optimized and parallelized. The ability of MCDP to investigate ordered polymers have been tested by simulating two complex systems: (1) the crystal structure of poly(4‐methyl‐1‐pentene), and (2) the biphasic structure of poly(α‐octyl‐β‐L‐aspartate), a comb‐like polyamide derived from β‐amino acids. The results obtained from MCDP simulations demonstrates the efficiency and reliability of this method to study both the NVT and NPT behavior of ordered dense polymers. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 162–171, 2001     

Sorption and diffusion of low molecular weight gases and vapors in glassy polymers at high concentration of sorbate

A theoretical approach has been developed to describe the sorption and diffusion processes of low weight molecular gases and vapors in polymers at wide ranges of sorbate concentration. The equation of an S‐shaped gas sorption isotherm in glassy polymer matrix has been derived. The concentration dependence of the sorbate molecule diffusion coefficient has been established. For an S‐shaped sorption isotherm, this dependence is nonmonotonous. The conditions of cluster formation of sorbate molecules have been analyzed within the proposed approach, in which it is possible to determine a correlation between these conditions and parameters of sorption isotherm. The comparison of the experimental and theoretical data provides an assessment of the microscopic characteristics of investigated polymer–vapor systems, such as the distances between vapor molecules in a matrix corresponding to intermolecular repulsion and attraction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2314–2323, 1999     

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.     

Synthesis of molecular objects: Two-dimensional polymers

Throughout this century polymer science has studied the linear chain and its architectural derivatives which include familiar forms such as the branched chain and the three dimensional network. Other derivatives with unique properties have been investigated more recently and include macromolecular rings, dendrimers, stars, combs and ladders. The objective of this work is to depart from the focus on linear chains and explore the “bulk” synthesis and properties of polymer molecules that can be considered molecular objects. Ideal molecular objects should be macromolecules with well defined shapes that persist as systems transform reversibly from solids to melts or solutions. The limited access to conformational space which is required in order to define and maintain shape in liquid and solid states of the system is an unusual molecular characteristic in common polymers. Our ability to create such objects through bulk reactions of reasonable scale will undoubtedly extend the current boundaries of polymer science and technology. Shapes that are particularly interesting are those not common in the conformational space of linear chains, for example, two-dimensional polymers shaped as plates and macromolecular bundles shaped as cylinders or parallelepipeds. The molecular object to be discussed in this lecture is a rigid and anisotropic two-dimensional polymer with planar dimensions greater than its thickness and a shape-granting skeleton built by covalent bonds. We have so far developed three different strategies for their synthesis, all involving systems in which reactive oligomers organize spontaneously into the necessary planar assemblies to form the object. In one strategy molecular recognition driven by homochiral interactions plays a key role in the formation of two-dimensional polymers.¹ A different methodology relies on entropy-driven nanophase separation in rodcoil block molecules in which a rigid segment is covalently bonded to a flexible one sharing the same backbone. The third strategy involves the folding of oligomers into hairpin structures which self assemble into two-dimensional liquids. The lecture will also describe examples of unique properties that could be achieved in materials containing these rigid two-dimensional objects. These examples will include bulk materials with self-organized surfaces and also remarkably stable nonlinear optical properties.     

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface II. Saturated heterogeneous polymer layers

Surface area exclusion chromatography (SAEC) was employed to determine the individual relaxation of polymer molecules within a saturated heterogeneous layer composed of two polymers of different molecular characteristics. The investigations focused on three systems differing in molecular weight and/or hydrolysis grade. The molecular relaxation process was determined to be different within the heterogeneous layer when compared with the behavior of the same polymer in the homogeneous layer. The modifications in the relaxation process of a given polymer were imposed by the interfacial characteristics of the second polymer. Finally, in heterogeneous layers, the relative variation of the interfacial area of the two polymers is expressed in a single relationship.     

Thermotropic liquid crystalline polymers. I. Cholesterol-containing polymers and copolymers

An approach to the creation of thermotropic cholesterol-containing liquid crystalline polymers by the chemical binding of cholesterol molecules with side chains of comblike polymers is presented. This type of structure permits a decrease in the steric hindrances provided by the backbone chains for the purpose of realizing the liquid crystalline state. A number of new cholesteric esters of poly(N-methacryloyl-ω-aminocarbonic acid)s (PChMAA-n) with different side-chain lengths (n = 2–11) as well as a series of copolymers of ChMA-n with n-alkylacrylates and n-alkylmethacrylates have been synthesized. The experimental evidence of liquid crystalline structure formation in these polymers in glass, viscoelastic, and fluid states is discussed. Molecular and supermolecular structures of cholesterol-containing comblike polymers have been studied and the model of macromolecular packing in the liquid crystalline state is proposed. It is shown that the existence of a layered order of side methylene groups together with ordering of cholesterol groups is necessary to the production of the liquid crystalline state in these polymers.     

Competitive adsorption of neutral comb polymers and sodium dodecyl sulfate at the air/water interface

The interfacial behavior of aqueous solutions of four different neutral polymers in the presence of sodium dodecyl sulfate (SDS) has been investigated by surface tension measurements and ellipsometry. The polymers comprised linear poly(ethylene oxide) with low and high molecular masses (10(3) and 10(6) Dalton (Da), respectively), and two high molecular mass methacrylate-based comb polymers containing poly(ethylene oxide) side chains. The adsorption isotherms of SDS, determined by Gibbs analysis of surface tension data, are nearly the same in the presence of the high molecular mass linear polymer and the comb polymers. Analysis of the ellipsometric data reveals that while a single surface layer model is appropriate for films of polymer alone, a more sophisticated interfacial layer model is necessary for films of SDS alone. For the polymer/surfactant mixtures, a novel semiempirical approach is proposed to determine the surface excess of polymer, and hence quantify the interfacial composition, through analysis of data from the two techniques. The replacement of the polymer due to surfactant adsorption is much less pronounced for the high molecular mass linear polymer and for the comb polymers than for the low molecular mass linear polymer. This finding is rationalized by the significantly higher adsorption driving force of the larger polymer molecules as well as by their more amphiphilic structure in the case of the comb polymers.     

Molecular dynamics of solid polymers as revealed by deuteron NMR

Pulsed deuteron NMR spectroscopy is described, which has recently been developed to become a powerful tool for studying molecular dynamics in solid polymers. It is shown that by analyzing the line shapes of²H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. By applying these techniques to selectively deuterated polymers, motional mechanisms involving different segments of the monomer unit can be monitored. In addition, motional heterogeneities in glassy polymers can be detected. The information about polymer dynamics available now is illustrated by a number of experimental examples. The chain motion in the amorphous regions of linearpolyethylene is discussed in detail and it is shown that it can clearly be distinguished from the chain motion of an amorphous polymer above the glass transition, wherepolystyrene is used as an example. Localized motions in the glassy state are illustrated through the jump motion phenyl groups exhibit both in the main chain (polycarbonate) and as a side group (polystyrene). The latter polymers also serve as examples for detecting motional heterogeneity. Finally, the mobility in novel classes of systems,liquid crystalline polymers andpolymer model membranes as revealed by²H NMR are described.     

High-resolution NMR of crosslinked polymers: Effects of crosslinked density and solvent interaction

Measurements have been made of the dependence of nuclear magnetic resonance bandwidths of polymers on the degree of crosslinking. Poly(methyl methacrylates) and poly(hexadecyl acrylates) were studied. Three regions of behavior are apparent: (1) in lightly crosslinked materials, bandwidths are quite insensitive to the degree of crosslinking, and the networks behave almost as linear polymers in solution; (2) in moderately crosslinked material, bandwidths are significantly affected by the degree of crosslinking; and (3) in highly crosslinked materials, bandwidths are extremely sensitive to crosslink density, and the polymer peaks become so broad that they disappear almost completely. These results indicate that segmental motion of a polymer in solution is not a function solely of its molecular weight, and that a certain degree of crosslinking is required to restrict polymer motion at the segmental level. The solvent (benzene) peak is always a singlet in swollen poly(methyl methacrylate) systems with swelling ratios up to 6.4 (regions 1 and 2, above) but as the swelling ratio further decreases to 3.5 (region 3), the solvent peak splits into a doublet; this phenomenon may indicate the existence of two different arrangements of solvent molecules in the swollen network, for which interchange is not sufficiently rapid to produce a single line.     

Water vapor sorption and diffusion in glassy polymers

By establishing relationships between polymer structure and gas permeation behavior, significant advances have been made in designing materials for membrane separation of gas mixtures. However, the situation is not so well understood when water vapor is one of the components since water molecules may interact with the polymer (plasticization) or each other (clustering) in ways that complicate the structure-property relationships. In addition, accurate measurement of water sorption, diffusion, and permeation is more complicated than for gases because of the unique hydrogen bonding capability of water, e.g., its tendency to strongly adsorb on high-energy surfaces and high heat of vaporization. A progress report on a broad program to understand water sorption and diffusion in glassy polymers that may be of interest for membrane applications is outlined; specific strategies include studies of structurally related polymers and miscible blends of hydrophobic/hydrophilic polymer pairs.     

基于环糊精包结络合作用的大分子自组装

本文综述了基于环糊精包结络合作用的大分子自组装的研究进展,包括：（1) 线型、梳型、多臂星型或超支化聚合物与环糊精或其二聚体自组装形成多聚轮烷（分子项链）、多聚准轮烷、双多聚（准）轮烷、分子管、双分子管、超分子凝胶及其应用;（2）桥联环糊精与桥联客体分子自组装制备线型或超支化超分子聚合物;（3）温度、pH值、光及客体分子刺激响应智能体系; （4) 通过亲水性的环糊精线型均聚物与含金刚烷的疏水性聚合物之间的包结络合作用来制备高分子胶束及其空心球等。     

Synthesis and ordering of two-dimensional polymers

The work to be discussed in this lecture departs from the usual focus of polymer science on linear chains and explores the “bulk” synthesis and properties of polymer molecules that can be considered shape-persistent molecular objects. Shapes that are particularly interesting are those not common in the conformational space of linear chains, for example, two-dimensional polymers shaped as plates or discs and macromolecules shaped as cylinders or parallelepipeds. The lecture focuses on a molecular object which is a rigid and internally anisotropic two-dimensional polymer with planar dimensions greater than its thickness. The shape-granting skeleton of this two-dimensional polymer is built by covalent bonds. We have so far developed three different strategies for their bulk synthesis, all involving systems in which reactive oligomers organize spontaneously into the necessary planar assemblies to form the object. In one strategy molecular recognition events such as homochiral interactions play a key role in the formation of the two-dimensional flat polymers /1/. A different methodology relies on nanophase separation in rodcoil block molecules in which a rigid segment is covalently bonded to a flexible one sharing the same backbone. The third strategy involves the folding of oligomers into hairpin structures which self assemble into two-dimensional liquids. In these two last strategies the layered rodcoils or hairpins react to form the covalent backbones necessary to grant shape to the object. A computer simulation relevant to the experimental system suggests that large two-dimensional polymers can be formed by extremely short backbones. The lecture will also describe examples of unique properties in advanced materials that could emerge from these rigid two-dimensional objects. These examples include. materials with self-organized surfaces of high chemical definition and temporal stability, self assembling membranes, molecular reinforcement, and films with remarkably stable electrical or optical properties.     

New functional inorganic polymers containing phosphorus

The C=C bond plays numerous roles in polymer science. This moiety is used as a precursor to polymers by addition polymerization and has been incorporated into π-conjugated polymers. The addition polymerization reaction has been extended to P=C bonds and the first example of a poly(methylenephosphine) has been prepared. The new macromolecule is of moderate molecular weight (ca. 10⁴ g/mol) and the oxidized polymers are air-stable. Poly(p-phenylenephosphaalkene), the first π-conjugated polymer containing P=C bonds in the backbone, has been prepared. The UV/Vis spectrum of this polymer shows a red shift in λ_max when compared with molecular model systems.     

Creep rate spectroscopy: High-resolution analysis of relaxations and prediction of anomalies in mechanical behavior of solids

An original laser-interferometric creep rate spectroscopy method was applied to analysis of molecular motion in some polymers, composites and interpenetrating polymer networks. Its potentials for study of nanoscale dynamic/compositional heterogeneity in complex systems, of a peculiar relaxation behavior of polymer binder in composites, and for prediction of temperature anomalies in strength are demonstrated.     

由聚合物结构预测气体的透过性能

本文利用基团加和法,对20多种常见聚合物的自由体积和内聚能进行了计算。发现氧气和氮气在聚合物膜中的透过率与自由体积和内聚能的比值有直接关系。此比值越大,气体的透过率越大,透过率的对数与自由体积和内聚能的比值基本呈线性关系。据此,对未知聚合物可根据其化学结构,从已有的基团数据计算该比值,从而预测它对氧气和氮气的透过性能。     

Investigations of comblike polysiloxanes. I. The influence of spacer length on dielectric relaxation studies of aligned samples

Dielectric relaxation studies on aligned liquid-crystalline comblike polysiloxanes are presented. The polymers differ only in the length of the flexible spacer separating the mesogenic side groups from the polysiloxane backbone. The characteristic features of the observed relaxation process as a function of frequency and temperature, in both the liquid-crystalline and isotropic phases, are described, and the effect of the spacer length is discussed. Within the liquid-crystalline phase a narrow single loss process is observed, due to the relaxation of the mesogenic side groups around the polymer backbone, whereas in the isotropic phase a much broader loss curve is seen. The transition from an aligned polymer mesophase to the randomly aligned isotropic phase is also studied in detial, and comparison with earlier work on comblike polyacrylate and methacrylate liquid crystals is presented.     

Thermally Rearranged Polymer Membranes Containing Tröger's Base Units Have Exceptional Performance for Air Separations

The influence of segmental chain motion on the gas separation performance of thermally rearranged (TR) polymer membranes is established for TR polybenzoxazoles featuring Tröger's base (TB) monomer subunits as exceptionally rigid sites of contortion along the polymer backbone. These polymers are accessed from solution‐processable ortho‐acetate functionalized polyimides, which are readily synthesized as high‐molecular‐weight polymers for membrane casting. We find that thermal rearrangement leads to a small increase in d‐spacing between polymer chains and a dramatic pore‐network reconfiguration that increases both membrane permeability and O₂/N₂ selectivity, putting its performance above the 2015 upper bound.     

Thermally induced phase transition in helical comblike poly(beta-peptide)s: an atomistic simulation

Atomistic Monte Carlo (MC) simulations have been used to study a thermally induced phase transition in poly(alpha-octadecyl-beta,L-aspartate). Simulations were performed by using the parallelized version of Configurational Bias MC algorithm adapted to study comblike polymers. A total of 1.15. 10(6) steps were carried out for a molecular system constituted by 6240 atoms/pseudoatoms. Results were consistent with available experimental observations. The limitations of atomistic simulations to study large length-scale phenomena are discussed.     

SYNTHESIS AND CHARACTERIZATION OF A NEW COMBLIKE POLYMER BASED ON POLY (VINYL METHYL ETHER-ALT-MALEIC ANHYDRIDE) BACKBONE

A new comblike polymer host for polymer electrolyte was synthesized by reactingmonomethyl ether of poly (ethylene glycol) with poly (vinyl methyl ether alt-maleic anhydride)and endcapping the residual carboxylic acid with methanol. Butanone was selected as a solventfor the esterification in order to obtain a completely soluble product. The synthesis processwas traced through by IR. Compared with the model compounds, the presumed structure ofthis comblike polymer has been proved to be valid by ~(13)C NMR. The comb polymer is a whiterubbery solid. It can be dissolved in butanone and THF, and manifests good film formingability.     

Controlled Stacking and Unstacking of Peripheral Chlorophyll Units Drives the Spring‐Like Contraction and Expansion of a Semi‐Artificial Helical Polymer

Developing new strategies for controlling polymer conformations through precise molecular recognition can potentially generate a machine‐like motion that is dependent on molecular information—an important process for the preparation of new intelligent nanomaterials (e.g., polymer‐based nanomachines) in the field bordering between polymer chemistry and conventional supramolecular sciences. Herein, we propose a strategy to endow a helical polymer chain with dynamic spring‐like (contraction/expansion) motion through the one‐dimensional self‐assembly (aggregation/disaggregation) of peripheral amphiphilic molecules. In this developing system, we employed a semi‐artificial helical polysaccharide presenting peripheral amphiphilic chlorophyll units as a power device that undergoes contractive motion in aqueous media, driven by strong π–π interactions of its chlorophyll units or by cooperative molecular recognition of bipyridyl‐type ligands through pairs of chlorophyll units, thereby converting molecular information into the regulated motion of a spring. In addition, this system also undergoes expansive motion through coordination of pyridine. We anticipate that this strategy will be applicable (when combined with the established wrapping chemistry of the helical polysaccharide) to the development of, for example, drug carriers (e.g., nano‐syringes), actuators (stimuli‐responsive films), and directional transporters (nano‐railways), thereby extending the frontiers of supramolecular science.