SHAPE OF POLYMER CHAINS ON A TETRAHEDRAL LATTICE

The shape of unperturbed polymer chains was studied using the Monte Carlo technique on a tetrahedral lattice. The asphericity A, the ratios <L-2(2)>/<L-1(2)> and <L-3(2)>/<L-1(2)> were calculated for different Values of polymer chain length n, conformational energy epsilon (epsilon greater than or equal to 0) and temperature T. The asphericity A decreases with the increase of chain length and tends to reach its limiting value rapidly with the decrease of gamma (gamma = epsilon/k(B)T). For large n, A is about 0.525 +/- 0.005, the ratios <L-2(2)>/<L-1(2)> and <L-3(2)>/<L-1(2)> are about 2.7 and 12.0, respectively, and are almost independent of gamma, but for short chains, they depend on gamma.

Stretching strongly confined semiflexible polymer chain

By the so-called wormlike chain （WLC） model in polymer physics envision- ing an isotropic rod that is continuously flexible, the force-extension relations of semi- flexible polymer chains strongly constrained by various confinements are theoretically investigated, including a slab-like confinement where the polymer chains are sandwiched between two parallel impenetrable walls, and a capped nanochannel confinement with a circular or rectangular cross-section where the chains are bounded in three directions. The Brownian dynamics （BD） simulations based on the generalized bead-rod （GBR） model are performed to verify the theoretical predictions.

MONTE CARLO STUDY ON THE CRITICAL ADSORPTION POINT OF BONDFLUCTUATED POLYMER CHAINS TETHERED ON ADSORBING SURFACES

The behavior of three-dimensional bond fluctuation model chains tethered on an adsorbing fiat surface was simulated by the Monte Carlo method.The dependence of the number of surface contacts M on the interaction strengthεand the chain length N was investigated by a finite-size scaling law M = N;[a;+a;N;κ+ O((N;κ);)]forεnear the critical adsorption pointε;,i.e.,κ=（ε-ε;）/ε;closes to 0.The critical adsorption point was estimated to beε;=0.93,and the exponentsφ= 0.49 and l/v= 0.57.

DIGITAL ANALYSIS TECHNOLOGY FOR MORPHOLOGY OF POLYMER CHAIN COILS IN FLOW FIELDS

Polymer chain coils with entanglement is a crucial scale of structures in polymer materials since their relaxationtimes are matching practical processing times.Based on the phenomenological model of polymer chain coils and a new finiteelement approach,we have designed a computer software including solver,pre-and post-processing modules,and developeda digital analysis technology for the morphology of polymer chain coils in flow fields(DAMPC).Using this technology wemay simulate the morphology development of chain coils in various flow fields,such as simple shear flow,elongational flow,and any complex flow at transient or steady state.The applications made up to now show that the software predictions arecomparable with experimental results.

Dynamic Monte Carlo study on the probability distribution functions of tail-like polymer chain

The configurational properties of tail-like polymer chains with one end attached to a flat surface are studied by using dynamic Monte Carlo technique. We find that the probability distribution of the free end in z direction P（Rz） and the density profile p（z） can be scaled approximately by a factor β to be a length independent function for both random walking （RW） and self-avoiding walking （SAW） tail-like chains, where the factor β is related to the mean square end-to-end distance 〈RE〉. The scaled P（Rz） of the SAW chain roughly overlaps that of the RW chain, but the scaled p（z） of the SAW chain locates at smaller βz than that of the RW chain.

SEGMENT DENSITY PROFILES OF COMPACT POLYMER CHAINS CONFINED BETWEEN TWO PARALLEL PLANE WALLS

We use the pruned-enriched Rosenbluth method to investigate systematically the segment density profiles of compact polymer chains confined between two parallel plane walls. The non-adsorption case of adsorption interaction energy ε = 0 and the weak adsorption case of ε= -1 are considered for the compact polymer chains with different chain lengths N and different separation distances between two walls D. Several special entropy effects on the confined compact polymer chains, such as a damped oscillation in the segment density profile for the large separation distance D, are observed and discussed for different separation distances D in the non-adsorption case. In the weak adsorption case, investigations on the segment density profiles indicate that the competition between the entropy and adsorption effects results in an obvious depletion layer. Moreover, the scaling laws of the damped oscillation period Td and the depletion layer width Ld are obtained for the confined compact chains. Most of these results are obtained for the first time so far as we know, which are expected to understand the properties of the confined compact polymer chains more completely.

DYNAMIC MONTE CARLO STUDY ON THE CORRELATION BETWEEN SHAPE AND SIZE OF LINEAR POLYMER CHAINS

The correlation between shape and size of linear chains on the simple cubic lattice is investigated using a dynamicMonte Carlo technique. A positive correlation between the asphericity parameter A and the square of the end-to-end distanceR^2, as well as that between A and the square of the radius of gyration S^2, is found for both RW and SAW chains, indicatingthat a chain conformation of small size is usually more spherical than one of large size. The result can explain why the shapeof the SAW chain deviate much more from a sphere than that of the RW chain, and can also explain the similar dependenceof size and shape on chain stiffness and on the distance of the first bead of a chain from an infinitely large flat surface.

A steered molecular dynamics study on the elastic behaviour of knotted polymer chains

In this paper the influence of a knot on the structure of a polymethylene （PM） strand in the tensile process is investigated by using the steered molecular dynamics （SMD） method. The gradual increasing of end-to-end distance, R, results in a tighter knot and a more stretched contour. That the break in a knotted rope almost invariably occurs at a point just outside the ＇entrance＇ to the knot, which has been shown in a good many experiments, is further theoretically verified in this paper through the calculation of some structural and thermodynamic parameters. Moreover, it is found that the analyses on bond length, torsion angle and strain energy can facilitate to the study of the localization and the size of a knot in the tensile process. The symmetries of torsion angles, bond lengths and bond angles in the knot result in the whole symmetry of the knot in microstructure, thereby adapting itself to the strain applied. Additionally, the statistical property of the force-dependent average knot size illuminates in detail the change in size of a knot with force f, and therefore the minimum size of the knot in the restriction of the potentials considered in this work for a PM chain is deduced. At the same time, the difference in response to uniaxial strain, between a knotted PM strand and an unknotted one is also investigated. The force-extension profile is easily obtained from the simulation. As expected, for a given f, the knotted chain has an R significantly smaller than that of an unknotted polymer. However, the scaled difference becomes less pronounced for larger values of N, and the results for longer chains approach those of the unknotted chains.

Partial pore blockage and polymer chain rigidification phenomena in PEO/ZIF-8 mixed matrix membranes synthesized by in situ polymerization

Nanostructured zeolitic imidazolate frameworks(ZIF-8) was incorporated into the mixture of poly(ethylene glycol) methyl ether acrylate(PEGMEA) and pentaerythritol triacrylate(PETA) to synthesize mixed matrix membranes(MMMs) by in situ polymerization for CO_2/CH_4 separation. The solvent-free polymerization between PEGMEA and PETA was induced by UV light with 1-hydroxylcyclohexyl phenyl ketone as initiator. The chemical structural characterization was performed by Fourier transform infrared spectroscopy. The morphology was characterized by scanning electron microscope. The average chain-to-chain distance of the polymer chains in MMMs was investigated by X-ray diffraction. The thermal property was evaluated by differential scanning calorimetry. The CH_4 and CO_2 gas transport properties of MMMs are reported. The relationship between gas permeation–separation performances or physical properties and ZIF-8 loading is also discussed. However, the permeation–separation performance was not improved in Robeson upper bound plot compared with original polymer membrane as predicted. The significant partial pore blockage and polymer rigidification effect around the ZIFs confirmed by the increase in glass temperature and the decrease in the d-spacing, were mainly responsible for the failure in performance improvement, which offset the high diffusion induced by porous ZIF-8.

Green Synthesized Liquid-like Dynamic Polymer Chains with Decreased Nonspecific Adhesivity for High-Purity Capture of Circulating Tumor Cells

The capture of circulating tumor cells(CTCs)is of great significance in reducing cancer mortality and complications.However,the nonspecific binding of proteins and white blood cells(WBCs)weakens the targeting capabilities of the capture surfaces,which critically hampers the efficiency and purity of the captured CTCs.Herein,we propose a liquid-like interface design strategy that consists of liquid-like polymer chains and anti-EpCAM modification processes for high-purity and high-efficiency capture of CTCs.The dynamic flexible feature of the liquid-like chains endows the modified surfaces with excellent antiadhesion property for proteins and blood cells.The liquid-like surfaces can capture the target CTCs and show high cell viability due to the environmentfriendly surface modification processes.When liquid-like surface designs were introduced in the deterministic lateral displacement(DLD)-patterned microfluidic chip,the nonspecific adhesion rate of WBCs was reduced by more than fivefold compared to that in the DLD chip without liquid-like interface design,while maintaining comparable capture efficiency.Overall,this strategy provides a novel perspective on surface design for achieving high purity and efficient capture of CTCs.

Synthesis of Branched Polyethylene via Bulky α-Diimine Nickel(II)-Catalyzed Ethylene Chain-Walking Polymerization

The catalysis of olefin polymerization through the chain-walking process is a subject of great interest. In this contribution, the successful synthesis of a Brookhart-type unsymmetrical α-diimine nickel catalyst Ni, which contains both dibenzhydryl and phenyl groups, was determined by X-ray crystallography. The compound has a pseudo-tetrahedral geometry at the Ni center, showing pseudo-C2-symmetry. Upon activation with modified methylaluminoxane (MMAO), Ni1 exhibits high catalytic activity up to 1.02 × 107 g PE (mol Ni h)−1 toward ethylene polymerization, enabling the synthesis of high molecular weight branched polyethylene. The molecular weights and branching densities could be tuned over a very wide range. The polymerization results indicated the possibility of precise microstructure control, depending on the polymerization temperature. The branching densities were decreased with increasing the polymerization temperature.

A STUDY ON THE STRUCTURAL TRANSITION OF A SINGLE POLYMER CHAIN BY PARALLEL TEMPERING MOLECULAR DYNAMICS SIMULATION

The structural transition of a single polymer chain with chain length of 100,200 and 300 beads was investigated by parallel tempering MD simulation.Our simulation results can capture the structural change from random coil to orientationally ordered structure with decreasing temperature.The clear transition was observed on the curves of radius of gyration and global orientational order parameter P as the function of temperature,which demonstrated structural formation of a single polymer chain.The linear relationships between three components of square radius of gyration R_（gx）~2,R_（gx）~2,R_（gz）~2 and global orientational order P can be obtained under the structurally transformational process.The slope of the linear relationship between x（or y-axis） component R_（gx）~2（or R_（gy）~2） and P is negative,while that of RL as the function of P is positive.The absolute value of slope is proportional to the chain length.Once the single polymer chain takes the random coil or ordered configuration,the linear relationship is invalid.The conformational change was also analyzed on microscopic scale.The polymer chain can be treated as the construction of rigid stems connecting by flexible loops.The deviation from exponentially decreased behavior of stem length distribution becomes prominent,indicating a stiffening of the chain arises leading to more and more segments ending up in the trans state with decreasing temperature.The stem length N_（tr） is about 21 bonds indicating the polymer chain is ordered with the specific fold length.So,the simulation results,which show the prototype of a liquid-crystalline polymer chain,are helpful to understand the crystallization process of crystalline polymers.

A STEERED MOLECULAR DYNAMICS SIMULATION ON THE ELASTIC BEHAVIOR OF ADSORBED STAR POLYMER CHAINS

Elastic behavior of 4-branched star polymer chain with different chain length N adsorbed on attractive surface is investigated using steered molecular dynamics （SMD） simulation method based on the united-atom （UA） model for branched alkanes. The simulation is realized by pulling up the chain via a linear spring with a constant velocity v = 0.005 nm/ps. At the beginning, the chain lies extensionally on adsorbed surface and suffers continuous deformations during the tensile process. Statistical parameters as mean-square radii of gyration 〈S2〉xy, 〈S2〉z, shape factor 〈δ〉, describing the conformational changes, sectional density 〈den〉 which gives the states of the chain, and average surface attractive energy 〈Ua〉, average total energy 〈U〉, average force 〈f〉 probed by the spring, which characterize the thermodynamic properties, are calculated in the stimulant process. Remarkably, distinguishing from the case in linear chains that there only exists one long plateau in the curve of 〈f 〉, the force plateau in our study for star chains is multiple, denoting different steps of desorption, and this agrees well with the experimental results in essence. We find during the tensile process, there are three characteristic distances Zc, Zt and Z0 from the attractive surface, and these values vary with N. When Z = Zc, the chain is stripped from the surface, but due to the form of wall-monomer interaction, the surface retains weak influence on the chain till Z = Zc. From Z = Zt, parameters 〈Ua〉, 〈U〉 and 〈f〉 respectively reach a stable value, while the shape and the size of the chain still need adjustments after Zt till Zo to reach their equilibrium states. Specifically, for short chain of N = 41, Zt and Z0 are incorporated. These results may help us to deepen the knowledge about the elastic behavior of adsorbed star polymer chains.

Translocation time of a polymer chain through an energy gradient nanopore

The translocation time of a polymer chain through an interaction energy gradient nanopore was studied by Monte Carlo simulations and the Fokker-Planck equation with double-absorbing boundary condi- tions. Both the simulation and calculation revealed three different behaviors for polymer translocation. These behaviors can be explained qualitatively from free-energy landscapes obtained for polymer translocation at different parameters. Results show that the translocation time of a polymer chain through a nanopore can be tuned by suitably designing the interaction energy gradient.

DLM/FD SIMULATION OF CHANNEL FLOW WITH FENE POLYMER CHAIN SUSPENSION

Distributed Lagrange Multiplier/Fictitious Domain （DLM/FD） method was employed to simulate the channel flow with polymer suspension. The polymer molecules were modeled as Finitely Extensible Nonlinear Elastic （FENE） chains and FENE chain cluster. The coiled stretched transition of FENE chains was examined and the change in configuration of FENE chains was presented. The average velocity profile of the fully developed channel flow with 64 FENE chains was given and fitted well with the power-law curve. The change of chain cluster configuration was also simulated. These simulations show that DLM/FD method is capable of simulating the motion of not only FENE chain, but also FENE chain cluster.

Superparticles Formed by Amphiphilic Tadpole-like Single Chain Polymeric Nanoparticles and Their Application as an Ultrasonic Responsive Drug Carrier

Herein, we report self-assembly of tadpole-like single chain polymeric nanoparticles （TPPs） and the ultrasonic response of the resultant superparticles. The TPPs are with an intramolecularly crosslinked poly（2-（methacryloyloxy）ethyl pent-4-ynoate）-rpoly（hydroxyethyl methacrylate） （PMAEP-r-PHEMA） chain as the ＂head＂ and a poly（2- （dimethylamino）ethyl methacrylate （PDMAEMA） linear chain as the ＂tail＂, and are pre- pared simply and emciently by Glaser-coupling of the pendant alkynes in the PMAEP-r- PHEMA block in the common solvent methanol. The formation of the TPPs was confirmed by gel permeation chromatograph, nuclear magnetic resonance spectroscopy, dynamic light scattering, static dynamic scattering, and transmission electron microscopy. In aqueous solution, the amphiphilic TPPs could self-assemble into regular superparticles, driven by aggregation of the hydrophobic ＂heads＂. Since in the structure there is no chain entanglement and the embedding of PDMAEMA chains disturb close-packing of the ＂heads＂, the superpartieles are responsive to a low-energy ultrasonic vibration, as evidenced by greatly enhanced release of the functional molecules from the superparticles by treatment of a low-energy ultrasound. Therefore, the superparticles should be very promising in the use as the drug carriers that can be manipulated from a long distance, considering that ultrasonic energy can be focused at a small area in a relatively long distance from the ultrasound-radiating source.

Evaluation of the clenbuterol imprinted monolithic column prepared by reversible addition-fragmentation chain transfer polymerization

To make more homogenous organic monolithic structure, reversible addition-fragmentation chain transfer （RAFT） process was employed in the synthesis of the clenbuterol imprinted polymer. In the synthesis, the influence of synthetic conditions on the polymer structure and separation efficiency was studied. The result demonstrated that the imprinted columns prepared with RAFT process have higher column efficiency and selectivity than the columns prepared with conventional polymerization in the present study, which may result from the higher surface area, smaller pore size and the narrower globule size distribution in their structures. The result indicated that RAFT polymerization provided better conditions for the clenbuterol imprinted monolithic polymer preparation. 2009 Xiang Chao Dong. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Synthesis,Crystal Structure and Fluorescence Property of the Ag(Ⅰ) Coordination Polymer Constructed by 2D[Ag(1,3-BIP)(PMA)_(0.5)]_n^(n-)Layers and 1D[Ag(1,3-BIP)(H_2O)]_n^(n+) Chains

A new AgO） coordination polymer, {[Ag（1,3-BIP）（H20）][Ag（1,3- BIP）（PMA）0.5.- 4H20}n （PMA = 1,2,4,5-benzenetricarboxylic acid, 1,3-BIP = 1,3-bis（imidazole）propane）, have been synthesized and characterized by single-crystal X-ray diffraction, powder XRD, FTIR, TGA and elemental analysis techniques. The single-crystal X-ray diffraction reveals that the title complex is formed by 1D polymeric cationic chains of [Ag（1,3-BIP）（H2O）]n^n＋ and 2D polymetric anionic layer of [Ag（1,3-BIP）（PMA）0.5]n^n-, which are further linked by intermolecular H-bonding to form a 3D supramolecular framework. In addition, the photoluminescence property of the title complex in the solid state at room temperature was also investigated.

One-dimensional Zigzag Chain Coordination Polymer [Zn(μ-phth)(imi)_2]_∞ Bridged by ο-Phthalato

The reaction of zinc carbonate with o-phthalic acid and imidazole in an aqueous-alcohol solution led to the formation of colorless crystals of [Zn(-phth)(imi)2]∞. Single-crystal X-ray analysis has revealed that the complex crystallizes in a monoclinic system, space group Pn with a = 8.394(2), b = 9.976(3), c = 9.959(3) ? ?= 104.409(4)? V = 807.6(4) ?, Z = 2, C14H12N4O4Zn, Mr = 365.65, Dc = 1.504 g/cm3, ?= 1.544 mm-1, F(000) = 372, the final R = 0.0466 and wR = 0.1171 for 1834 reflections with I >2(I). The complex displays a zigzag infinite chain structure in which each zinc (Ⅱ) center is coordinated by two oxygen atoms and two nitrogen atoms to generate a ZnN2O2 distorted tetrahedral geometry. The neighboring zinc atoms are bridged by the o-phthalate ligand. Each chain is linked by hydrogen bonds with its neighbors to form a three-dimensional coordination polymer.

Syntheses,Structures,and Photoluminescent Properties of Two Zn(Ⅱ)Coordination Polymers with Helical Chains Structures

Two novel coordination polymers with helical chains, {[Zn（L）（H2O）]·H2O}n（1） and {[Zn（L）（p-bix）]·3.5H2O}n（2）, where H2 L = 5-（4-hydroxypyridinium-1-ylmethyl） isophthalic acid and p-bix = 1,4-bis（imidazol-1-ylmethyl）benzene, have been hydrothermally synthesized, and charac-terized by elemental analysis, powder X-ray diffraction（PXRD）, IR, thermal gravimetric analyses（TGA） and also by single-crystal X-ray diffraction. Both complexes 1 and 2 crystallize inmonoclinic, space group P21/c. Compound 1 displays a two-dimensional（2D） structure with two distinct types of helical chains; 2 shows a layered coordination polymer with two types of helical chains and features an interesting 2D→3D interdigitated architecture. Meanwhile, the luminescent properties of 1 and 2 have also been investigated in detail.