Linear Polymer Chains Research Articles

Gaussian analysis of Raman spectroscopy of acetic acid reveals a significant amount of monomers that effectively cooperate with hydrogen bonded linear chains.

Gaussian analysis of Raman spectroscopy reveals three significant structures in the liquid acetic acid (AA): linear chains involving C-H···O=C and O-H···O=C hydrogen bonding, cyclic dimers and dissociated monomers that can effectively cooperate with hydrogen bonded stacks of linear AA or polymer chains.

The role of topology and thermal backbone fluctuations on sacrificial bond efficacy in mechanical metalloproteins

Sacrificial bonding is a ubiquitous cross-linking strategy for increasing toughness that is found throughout nature in various biological materials such as bone, wood, silk and mussel byssal threads. However, the molecular mechanism of sacrificial bonding remains only poorly understood. Molecular modeling possesses a strong potential to provide insights into the behavior of these cross-links. Here we use Monte Carlo simulations to investigate the effect of reversible sacrificial binding sites on the mechanical properties of single linear polymer chains based on load-bearing metalloproteins found in the mussel byssus. It is shown that the topology of the bonds determines the position and spacing of sacrificial force peaks, while the height of these peaks is intimately tied to the magnitude of thermal fluctuations in the chain that are dependent on effective chain length. These results bear important implications for understanding natural systems and for the generation of strong and ductile biomimetic polymers.

Versatile coordination environment and interplay of metal assisted secondary interactions in the organization of supramolecular motifs in new Hg(II)/PhHg(II) dithiolates

New mercury(II) complexes of the form [PhHg(L)] (L=L1 (1), L2 (2), L3′ (3), L4=(4)); [Hg(L)2] (L=L5 (5), L4 (7) and [Hg2(L6)4] (6) have been synthesized and characterized by micro analysis and X-ray crystallography. Both 1 and 2 are linear; complex 2 revealed intramolecular Hg⋯O bonding interactions. Complex 3 possesses T-shaped geometry in a linear polymeric chain motif. Although serendipitously formed, 3 is the first example of a metal trithioxanthate complex. 4 is a typical dimer and in 5, a helical chain motif is generated via Hg⋯S contacts. 6 is a dinuclear complex with distorted square pyramidal geometry. 7 is mononuclear with a tetrahedrally coordinated mercury(II) ion. All complexes are luminescent in solution and solid state. In 2 the nature of Hg⋯O interactions have been assessed by DFT calculations and the electronic transitions in 3 have been corroborated by TDDFT calculations.

Self-assembly of cobalt(ii) and zinc(ii) tetranitrooctaethylporphyrin via bidentate axial ligands: synthesis, structure, surface morphology and effect of axial coordination

A series of remarkably stable supramolecular architectures of cobalt(II) and zinc(II) tetranitrooctaethylporphyrins (tn-OEP) mediated by long and conjugated bipyridyl axial ligands (L) have been synthesized in one pot in excellent yields and structurally characterized. Linear 1D polymeric chains were observed in the X-ray structures of the six-coordinated Co(II) complexes in which all the porphyrin units are aligned parallel to each other to have so-called “shish kebab” like architectures in order to maintain offset-stacked overlap. In contrast, ZnII(tn-OEP) forms five-coordinate porphyrin dimers [ZnII(tn-OEP)]2·L with “wheel-and-axle” like architectures which are then self-aggregated in a perpendicular manner to fill space more effectively. The surface patterns of the polymeric molecules on HOPG surface are found similar as observed in the X-ray structures. Large downfield shift and the peak broadening of the axial ligand resonances in solution are discerned in the 1H NMR of [CoII(tn-OEP)]·L which is due to the contiguity to the paramagnetic Co(II) center. In contrast, upfield shift of the 1H NMR resonances of the axial ligand L are observed for [ZnII(tn-OEP)]2·L due to the shielding effect of porphyrin ring current which confirms the retention of the solid state structures in solution. However, the axial ligation with monodentate pyridine to CoII(tn-OEP) produces six-coordinate complex [CoIII(tn-OEP)(py)2]+ in which Co(II) spontaneously oxidizes to Co(III) in air. The first 1e-reductive response in cyclic voltammetry of [CoIII(tn-OEP)(py)2]+, which is assigned as CoIII/CoII, has been shifted to −0.42 V which explains why addition of pyridine to CoII(tn-OEP) in air results in spontaneous oxidation of Co(II) to Co(III). Weaker ligand field strength of bidentate bipyridyl axial ligand L compared to its smaller monodentate counterpart pyridine has also been demonstrated here.

Computer Simulation Study on Solubility of Three-Dimensional Polymer Multiple Chain System

The author adopts Monte Carlo compute method to simulate the linear polymer chain lattice model in multiple chain systems of chain length n=20, 50, 100 while the volume fraction Φ=0.125, and makes a research on the variational situation of the solubility with changing of the interaction energy between solvent molecule and polymer chain segment molecule εPS. The results indicate, the solvent become not benefit to solve, the polymer chain turn into the ruleless coil shape, and the polymer groups overlap across with the increase of the interaction energy εPS.

Topology Evolution in Polymer Modification

A recent numerical method has opened new opportunities in multidimensional population balance modeling. Here, this method is applied to a full three‐dimensional population balance model (PBM) describing branching topology evolution driven by chain end to backbone coupling. This process is typical for polymer modification reactions, e.g., in polyethylene, where initially linear polymer chains undergo hydrogen abstraction, and subsequent branching or scission. Topologies are distinguished by chain ends, number of branches, and number of reactive ends. The resulting time dependent trivariate distribution is utilized to extract various distributive properties of the polymer. The results exhibit excellent agreement with data from Monte Carlo simulations.

In situ STM and ex situ XPS examination of the adsorption and polymerization of metanilic acid and aniline on Au(1 1 1) electrode

Oxidation of aniline and its derivatives can yield cationic radicals, which induce chain reactions to produce polymeric materials with notable conductivity. When these events occur on ordered electrode surface, admolecules can be adsorbed in some specific manner that guides reactions to proceed in some specific directions to yield products with well-defined conformations. This study employed cyclic voltammetry, X-ray photoemission spectroscopy (XPS), and in situ scanning tunneling microscopy (STM) to study the adsorption and polymerization of metanilic acid (MA) in 0.5MH2SO4. MA molecules were adsorbed in highly ordered adlattices characterized as Au(111) – (19×31) and (27×31) at 0.5 and 0.8V (vs. reversible hydrogen electrode). These adlattices were displaced by bisulfate anions at E>1.0V. MA molecules still could be oxidized to yield polymer molecules, which lacked a well-defined structure. By contrast, MA and aniline molecules could be coadsorbed in a highly ordered Au(111) – (4×23) structure at 0.8V in 0.5M H2SO4+30mM aniline+3mM MA, which led to anisotropic oxidative polymerization in the 〈121〉 directions of the Au(111) electrode surface. According to ex situ XPS results, the as-produced linear polymeric chains were mainly polyaniline (PAN), rather than copolymer of aniline and MA. The surface structure and polymerization of aniline and MA varied greatly with their molar ratios. No ordered adlayer was observed in solution containing equal amounts (30mM) of MA and aniline.

Isotactic Polystyrene Reactor Blends with Tailored Bimodal Molar Mass Distribution

Reactor blend formation of soluble highly isotactic polystyrene (iPS) enables tailoring of bimodal iPS molar mass distributions containing variable amounts of ultrahigh molar mass iPS (UHMWiPS). A key feature is the facile iPS molar mass control, achieved by homogeneous catalytic styrene polymerization on a MAO-activated titanium bisphenolate catalyst, using 1,9-decadiene as chain transfer agent. Whereas UHMWiPS (Mw of 947 000 g mol–1) is formed in the absence of the diene, the molar mass Mw increases from 191 000 to 482 000 g mol–1 with decreasing diene/styrene molar ratio. In a cascade of two parallel reactors, polymerizing styrene in the presence and the absence of diene, the mixing ratio of the resulting two iPS solutions governs the UHMWiPS content of the reactor blends (RB-2). Hence, the contents of iPS and UHMWiPS are varied without affecting the average molar mass of both blend components. In reactor blends (RB-1), produced in a single reactor with delayed diene injection, molar mass and polydispersity of iPS/UHMWiPS as well as molar mass of the iPS fraction and UHMWiPS depend on the diene/styrene molar ratio and the delay time of the diene injection. In this study, we investigate the influence of both iPS molar mass and iPS molar mass distributions on crystallization behavior and viscoelastic properties. The correlation of zero shear viscosity with the iPS molar mass exhibits scaling of 3.4, typical for linear polymer chains. Below 10 wt % UHMWiPS content, bimodal iPS molar mass distribution enhances processability by shear thinning.

Thermal Properties of Particle Brush Materials: Effect of Polymer Graft Architecture on the Glass Transition Temperature in Polymer‐Grafted Colloidal Systems

SummaryThe governing parameters controlling the glass transition temperature of polymer‐grafted particle systems are analyzed for the particular case of polystyrene (PS)‐grafted silica colloids in the dense grafting limit. At a given degree of polymerization of surface‐grafted chains the glass transition temperature is found to increase as compared to linear chain polymers of equivalent degree of polymerization. The difference in the glass transition temperature between polymer‐grafted particle systems and their respective linear polymer analogs increases with decreasing degree of polymerization of surface‐grafted chains and levels off at similar plateau values for particle brushes of distinct particle core size. The trend toward increased glass transition temperature is interpreted as a consequence of the increased steric hindrance in polymer‐grafted particles that counteracts the relaxation of surface‐grafted polymer chains. The increase in glass transition temperature is shown to be approximately consistent with the chain conformational regimes that are predicted on the basis of a Daoud‐Cotton type scaling model.

Efficient Separation of Long Polymer Chains by Contour Length and Architecture.

On the basis of theoretical considerations and computer experiment, we suggest a new technique for separation of polymer molecules. The method is based on filling an array of nanochannels with macromolecules whereby the subsequent ejection time depends strongly on small differences in the end-to-end distances of elongated configurations inside the nanotubes. In contrast to conventional methods for chromatographic separation, the efficiency of the proposed method increases with growing molecular length of the chains. The method appears promising also for the separation of ring from linear polymer chains.

Fluorescent Silver Nanoclusters in Condensed DNA

We study the formation and fluorescent properties of silver nanoclusters encapsulated in condensed DNA nanoparticles. Fluorescent globular DNA nanoparticles are formed using a dsDNA-cluster complex and polyallylamine as condensing agents. The fluorescence emission spectrum of single DNA nanoparticles is obtained using tip-enhanced fluorescence microscopy. Fluorescent clusters in condensed DNA nanoparticles appear to be more protected against destructive damage in solution compared to clusters synthesized on a linear polymer chain. The fluorescent clusters on both dsDNA and ssDNA exhibit the same emission bands (at 590 and 680 nm) and the same formation efficiency, which suggests the same binding sites. By using density functional theory, we show that the clusters may bind to the Watson-Crick guanine-cytosine base pairs and to single DNA bases with about the same affinity.

Porous and Nanorod-Like Coordination Polymers Assembled from a New V-Shaped Bis(1,2,4-triazolyl)tripyridine Ligand

Six complexes based on a new rigid V-shaped ligand, 2,6-bis(3-(pyrid-4-yl)-1,2,4-triazolyl)pyridine (2,6-H2bptp), namely, [Cd4(2,6-bptp)2(d-cam)(l-cam)(H2O)2]n·4nH2O (1), [Cd2(2,6-Hbptp)2(Hbtc)]n·4nH2O (2), [Zn(2,6-bptp)(H2O)]n·nH2O (3), [(Mo8O26)Cu2(2,6-H2bptp)2]n (4), [Co(2,6-H2bptp)2][Mo8O26]0.5·5H2O (5), and [(PMo12O40)Ag(2,6-H4bptp)]·2H2O (6) (d/l-H2cam = d/l-camphoric acid; H3btc = 1,3,5-benzenetricarboxylic acid), have been synthesized under hydrothermal conditions. Among these complexes, 2,6-H2bptp adopts seven types of coordination modes; all display a central tridentate chelating plane. Complex 1 possesses a 3D porous metal–organic framework that exhibits an intriguing sandwich-like motif. Complex 2 is a 1D nanorod-like coordination polymer with a square section of 1.11 × 1.06 nm2. Complex 3 exhibits a 1D zigzag chain structure, which is extended to a supramolecular double-chain by hydrogen bonding. In complex 4, polyoxometalate β-Mo8O264– links Cu2(2,6-H2bptp)24+ dimer to form a 1D linear chain polymer. Complex 5 displays a 3D supramolecular architecture with nanosized tunnels in which β-[Mo8O26]4– clusters embed. Complex 6 is a mononuclear silver complex constructed from Ag(2,6-H4bptp)3+ and [PMo12O40]3– pieces, which is further extended to a 3D supramolecular framework. The metal–organic frameworks of 1 and 2 are thermally stable up to 440 °C. Both Cd(II) complexes emit blue luminescence originating from ligand-centered emission. Complex 4 shows weak antiferromagnetic coupling in the Cu2(2,6-H2bptp)24+ dimer.

Poly(vinylcaprolactam)-Based Biodegradable Multiresponsive Microgels for Drug Delivery

Poly(vinylcaprolactam) (PVCL)-based biodegradable microgels were prepared for the biomedical application as drug delivery system via precipitation polymerization, where N,N-bis(acryloyl) cystamine (BAC) served as cross-linker, methacrylic acid (MAA) and polyethylene glycol (PEG) methyl ether methacrylate acted as comonomers. The microgels with excellent stability had distinct temperature sensitivity as largely observed in the case of PVCL-based particles and their volume phase transition temperature (VPTT) shifted to higher temperature with increasing MAA content and ambient pH. In the presence of reducing agent glutathione (GSH) or dithiothreitol (DTT), the microgels could be degraded into individual linear polymer chains by the cleavage of the disulfide linkages coming from the cross-linker BAC. The microgels could effectively encapsulate Doxorubicin (DOX) inside and presented stimuli-triggered drug release in acidic or reducing environment. The results of the cytotoxicity assays further demonstrated that the blank microgels were nontoxic to normal cells while DOX-loaded microgels presented efficient antitumor activity to HeLa cells.

Monte Carlo Simulation on Conformation Properties of Polymer Multiple Chain System

The author adopts Monte Carlo compute method to simulate the linear polymer chain lattice model in multiple chain systems of different volume fraction Φ while chain length n=50, and makes a research on the variational situation of the size (measured with the mean-square end-to-end distance <R2> and the mean-square radius of gyration <S2>), shape (measured with the mean asphericity factor ) with changing of the interaction energy between solvent molecule and polymer chain segment molecule εPS. Results indicate <R2>, <S2> and have the changing rules that they become small with the increase of the εPS.

The effect of material characteristics and mould parameters on the thermoforming of thick polypropylene sheets

Two grades of 5 mm thick polypropylene (PP) sheets, one having linear polymer chains (PP-TF-1) and the other having long-chain branches (PP-TF-2), were drape formed, using moulds of different parameters. Single-sided heating of sheet was found to be suitable only at lower depths of draw. Double-sided heating gave good part shape conformance at all depths of draw. PP-TF-2 was found to have lower crystallinity than PP-TF-1, suggesting that it would have a lower sagging tendency and would give parts with more uniform wall thickness distribution. This was confirmed in formability studies. At higher depths of draw, an increase in draft angle was found to give more uniform wall thickness distribution, maintaining reasonable values of wall thickness. At lower depths of draw, draft angle was found to have no influence on product quality. Irrespective of material characteristics and other mould parameters, only moulds with generous values of corner radii gave strong corners.

Computer Simulation on Conformation Properties of Polymer Chain

The author adopts Monte Carlo compute method to simulate the linear polymer chain lattice model in multiple chain systems of chain length n=20, 50, 100 while the volume fraction Φ=0.125, and makes a research on the variational situation of the size (measured with the mean-square end-to-end distance <R2> and the mean-square radius of gyration <S2>), shape (measured with the mean asphericity factor <A>) with changing of the interaction energy between solvent molecule and polymer chain segment molecule εPS. Results indicate <R2>, <S2> and <A> have the changing rules that they become small with the increase of the εPS

Single-Molecule Study on Polymer Diffusion in a Melt State: Effect of Chain Topology

We report a new methodology for studying diffusion of individual polymer chains in a melt state, with special emphasis on the effect of chain topology. A perylene diimide fluorophore was incorporated into the linear and cyclic poly(THF)s, and real-time diffusion behavior of individual chains in a melt of linear poly(THF) was measured by means of a single-molecule fluorescence imaging technique. The combination of mean squared displacement (MSD) and cumulative distribution function (CDF) analysis demonstrated the broad distribution of diffusion coefficient of both the linear and cyclic polymer chains in the melt state. This indicates the presence of spatiotemporal heterogeneity of the polymer diffusion which occurs at much larger time and length scales than those expected from the current polymer physics theory. We further demonstrated that the cyclic chains showed marginally slower diffusion in comparison with the linear counterparts, to suggest the effective suppression of the translocation through the threading-entanglement with the linear matrix chains. This coincides with the higher activation energy for the diffusion of the cyclic chains than of the linear chains. These results suggest that the single-molecule imaging technique provides a powerful tool to analyze complicated polymer dynamics and contributes to the molecular level understanding of the chain interaction.

Syntheses, crystal structures and spectral properties of 1D tetracyanonickelate(II) complexes with 1-ethylimidazole

Three new cyano-bridged tetracyanonickelate(II) complexes with 1-ethylimidazole (etim) ligand, [Ni(etim)4Ni(μ-CN)2(CN)2]n (1), [Zn(etim)4Ni(μ-CN)2(CN)2]n (2) and {[Cd(etim)4Ni(μ-CN)2(CN)2]2·2H2O}n (3) have been synthesized and characterized by spectroscopic (IR and Raman) and X-ray diffraction techniques. According to the crystallographic data, it was understood that the complexes with the chain 2,2-TT structures belong to P−1 space group of triclinic crystal system. In the complexes, it was observed that Ni(II), Zn(II) and Cd(II) ions have distorted octahedral geometries. In the [Ni(μ-CN)2(CN)2]2− anion, the Ni(II) ion is coordinated by the four carbon atoms of the four cyano ligands, and exhibits square-planar coordination geometry. The crystallographic analyses reveal that the crystal structures of complexes 1–3 are one dimensional linear chain polymers and these chains are held together by the CH⋯π, CH⋯Ni and hydrogen bonding interactions, forming three-dimensional networks.

Dendritic Spherical Polymer Brushes: Theory and Self-Consistent Field Modeling

Equilibrium structural properties of polymer brushes formed by dendrons grafted via the root segment onto spherical surfaces (dendritic spherical polymer brushes, DSPB) are studied by means of the Scheutjens–Fleer self-consistent field (SF-SCF) numerical approach and scaling analysis. In particular, we focus on the effects of the variable curvature of the surface on the polymer volume fraction distribution and extension of the individual dendrons in DSPB. A systematic comparison with spherical polymer brushes formed by linear polymer chains (LSPB) end-grafted to the surfaces of the same curvature radii is performed. We demonstrate that the difference in internal structural organization of DSPB and LSPB is most pronounced at small curvature radius of the grafting surface. In particular, the radial distribution of polymer volume fraction in DSPB is close to uniform, whereas in LSPB it decays in the radial direction following a power law. The quasi-plateau polymer volume fraction distribution in DSPB is ensu...

Combining Ring-Opening Multibranching and RAFT Polymerization: Multifunctional Linear–Hyperbranched Block Copolymers via Hyperbranched Macro-Chain-Transfer Agents

The synthesis of a hyperbranched macro-chain-transfer agent for RAFT polymerization of functional methacrylate or methacrylamide monomers was achieved by selectively attaching one single CTA onto hyperbranched polyglycerol dendron analogues. The combination of ring-opening multibranching polymerization of glycidol and subsequent RAFT polymerization of the hyperbranched macro-chain-transfer agents created a new route to a variety of multifunctional linear–hyperbranched block topologies. All linear–hyperbranched block copolymers could be synthesized with controlled molecular weight (Mn = 3.2–43.7 kg/mol) and low polydispersity (PDI = 1.15–1.34). As first examples for this universal approach, we present block copolymer syntheses with thermoresponsive methacrylate (tri(ethylene glycol) methyl ether methacrylate) and biocompatible methacrylamide (2-hydroxypropylmethacrylamide). Because of the presence of dithiobenzoate esters at the end of each linear polymer chain end, selective end-group modification with fu...