Rigid-chain Polymers Research Articles

Anisotropic Nano-/Microparticles from Diversified Copolymers by Solvent-Mediated Self-Assembly.

Effective synthesis of anisotropic nano-/microparticles (APs) by the copolymers is of great significance in nanomaterials and nanotechnology. However, achieving regulation of the morphology, composition, property, and particle size of anisotropic nano-/microparticles (APs) with diversified copolymers is difficult due to complex mechanism and formation conditions. In this work, a versatile one-pot solvent-mediated self-assembly (SmSa) strategy had been proposed for the facile one-pot synthesis of shape-tunable anisotropic nano-/microparticles (StAPs). In addition, the formation mechanism of StAPs was determined through numerous characterization methods related to morphology and element distribution. The results revealed that the anisotropic architectures of StAPs were closely related to the nature of poly(methylacrylic acid-methyl methacrylate-butyl acrylate) (L1) and poly(butyl acrylate-styrene) (L2) polymer chains imparted by polymer blocks of different domains. Therefore, the ordered assembly of the rigid and hydrophobic L2 polymer chains in micelles consisting of the flexible and amphiphilic L1 and solvent could be successfully carried out under the mediation of increasing solvent polarity and the strong adsorption of poly(vinylpyrrolidone) for L2. Furthermore, the developed versatile SmSa strategy and the obtained StAPs play an essential role in the development of nanoscience and nanotechnology. Particularly given its adjustable emulsifying properties at different pH values, as well as numerous sites for further modification by fluorescent or other components, it can be employed to synthesize a wide range of functional materials.

Design of monomeric units for rigid aromatic polymers

The effect of structural inhomogeneities on the equilibrium flexibility of rigid-chain aromatic polymers containing complex condensed cycles in the main chain has been studied. The non-flatness of complex condensed cycles leads to a significant decrease in the equilibrium flexibility of rigid-chain polymers based on them and, consequently, to a deterioration of their mechanical properties. It is shown that the non-planarity of these cycles can reduce the Kuhn segment by several times. The introduction of phenyl substituents into condensed cycles reduces the non-planarity of such cycles and makes it possible to obtain a polymer with sufficiently high physical characteristics.

Dielectric and calorimetric signatures of chain orientation in strong and tough ultrafine electrospun polyacrylonitrile

Ultrafine diameter fibers of polyacrylonitrile (PAN), obtained from electrospinning, have huge potential for structural applications since they exhibit an unusual combination of strength and toughness. However, the difficulty to characterize their supramolecular architecture limits their production at the industrial scale. In this work, the glass transition of electrospun nanofiber mats of PAN was investigated by means of thermal analysis techniques. Modulated temperature differential scanning calorimetry (MT–DSC) and dielectric relaxation spectroscopy (DRS) were used, and relaxation parameters characteristic of the glass transition were obtained. Reduction in average fiber diameter resulted in broadening of the glass transition and a shift of its midpoint to higher temperatures as observed by MT–DSC, revealing additional level of constraints in the amorphous phase. The DRS curves, obtained above the calorimetric signature of the glass transition, superimpose independently on the fiber diameter. This result, which contrasts with MT–DSC observations, shows that the constraint of mobility evidenced at the glass transition, is suppressed when driving the fiber mat to higher temperatures. The dielectric strength increases with temperature, revealing an increase in the density of dipoles participating to the relaxation dynamics. This result, commonly attributed to the progressive mobilization of initially constrained amorphous phase, supports the hypothesis that electrospinning process induces higher level of polymer chain orientation at small fiber diameters, which fades away when crossing the glass transition. The orientation impacts the temperature dependence of the relaxation time close to the glass transition, as it shows higher deviation from Arrhenius behavior with the decrease of the fiber diameter. This leads to an increase of the fragility index which comes in opposition to the decrease in the cooperativity length, estimated from the temperature fluctuation approach of the cooperative rearranging region (CRR) concept. To explain this result, both volume and thermal contributions of the fragility index have been calculated, and a strong increase in the thermal contribution has been observed for the most oriented material. This result is interpreted as a signature of an increase in the polymer chain rigidity.

A synergistic analysis of drag reduction on binary polymer mixtures containing guar gum

Drag reduction by the addition of polymer additives has been widely studied. However, there are only a few studies on binary polymer mixtures, here named blends. In this work, xanthan gum, polyacrylamide and poly(ethylene oxide) were associated with guar gum and drag reduction was used as a parameter to determine the synergistic interaction between polymers. The aim was to verify the relation of the synergy with the rigidity of the polymeric chains, the molecular weights and the magnitude of the molecular interactions between the studied polymers. To that end, several ratios of mixtures were tested at different Reynolds numbers in a rotational rheometer with double-gap concentric cylinders geometry. Finally, experiments were done to verify the behaviour of the blends over time at a fixed Reynolds number. From all these tests, it was documented that blends containing rigid chain polymers show positive synergism in the interaction in at least one of the ratios and that this interaction is more pronounced when the molecular weights are closer and intermolecular forces are stronger. It was also noted that, in general, blends are great substitutes for solutions containing only one type of polymer.

The Effect of Uniaxial Extrusion on the Degree of Reinforcement of Nanocomposites Polyvinyl Chloride/Boron Nitride

The influence of uniaxial extrusion on the structure, molecular characteristics, and properties of polymer/2D nanofiller nanocomposites is elucidated by example of polyvinyl chloride/boron nitride nanocomposites. The extrusion is found to cause a drastic (by 2.5 times) increase in statistical rigidity of polymer chains in the nanocomposite matrix determined by their characteristic ratio. The characteristic ratio for unoriented samples is less than that for a polymer precursor, but exceeds the values for oriented specimens. Nanofiller particles (or their aggregates) form a fractal network (“skeleton”) in the polymer matrix, whose dimension increases upon uniaxial extrusion. This effect leads to a linear reduction of the percolation index in the percolation model of reinforcement of nanocomposites, which significantly affects the degree of their reinforcement. When the dimension reaches its threshold of 2.8, the percolation index changes values from positive to negative values, meaning the transition from the “ant” to the “termite” limit. This yields an abrupt (to ~150) increase in the degree of reinforcement of polymer nanocomposites at low nanofiller contents. The characteristic ratio of polymer chains of the nanocomposite matrix is closely related to the aggregation level of the 2D nanofiller, which depends on the number of boron nitride slabs in a “package” (tactoid). The relative fraction of interfaces serving as reinforcing elements in a nanocomposite structure by analogy with nanofillers is also a function of statistical rigidity of polymer chains in the matrix and increases with the characteristic ratio. The theoretical estimates in the context of the percolation model of reinforcement reveal the prospects in the improvement of the properties of polymer/2D nanofiller nanocomposites.

Enhancement of orientation of rigid polymer blocks by incorporating rod–coil block copolymer chains into metal–organic frameworks

AbstractIncorporation of polymer chains into metal–organic frameworks (MOFs) is a simple yet efficient method for improving the orientation of the polymer chains. However, due to their rigidity and high molecular weight, many rigid polymer chains are either not easily loaded into MOFs, or not easily aligned within the MOF channels. In this paper, we propose a strategy for enhancing the orientation of rigid blocks by incorporating rod–coil block copolymer chains into MOFs. In this strategy, on the one hand, the rigid blocks have a low molecular weight, so that the steric hindrance effect from the MOF channels could align the rigid blocks more efficiently. On the other hand, because the covalent bonds between the repeat units of the flexible blocks can rotate relatively easily, the steric hindrance effect from the flexible blocks can further help the rigid blocks to be oriented within the MOF channels. In confirmatory simulations, two all‐atom MOF models, [Zn2(BDC)2(TED)]n and [Zn2(BPDC)2(TED)]n (TED = triethylenediamine, BDC = 1,4‐benzenedicarboxylate, BPDC = 4,4′‐biphenyldicarboxylate), are established. With these MOF models, molecular dynamics simulations are performed for the rigid poly(phenylene vinylene) (PPV) chain and the rod–coil block copolymer PPV‐block‐polystyrene (PSt). Further, their respective degrees of orientation (DoOs) are calculated. Within [Zn2(BDC)2(TED)]n and [Zn2(BPDC)2(TED)]n, the DoOs of the rigid PPV blocks of PPV‐block‐PSt are 0.968 and 0.902, respectively, while the DoOs of the rigid PPV chains are 0.865 and 0.711, respectively. These calculation results prove the feasibility of our proposed strategy. © 2019 Society of Chemical Industry

Dissipative Particle Dynamics Simulation on Bonding Reaction Between Surface Modified Nanoparticles

A simulation study was carried out by using dissipative particle dynamics (DPD) method to explore the effects of properties of coating chains, such as length, density, rigidity of polymer chains, as well as the distance between nanoparticles on bonding reaction of coating chains grafted onto nanoparticles. The results show that bonding ratios of coated chains strongly depend on the length and density of coating chains. For nanoparticles with different coating densities, the optimum chain length for bonding reaction are varied. The rigidity of coating chains exhibits vigorous effects on bonding reaction that highly depends on chain lengths. DPD simulation can be used to study the bonding reaction between coated nanoparticles, which may help experimental synthesis of nanocomposites with excellent properties.

Specificities of Local Dynamics and Orientational State of Rigid-Chain Liquid-Crystal Polymers

Proton magnetic resonance (PMR) spectra and terahertz IR spectra of Vectra A950 fibers and granules and Armos fibers before and after heat treatment were obtained and analyzed in order to understand the molecular mobility mechanisms that ensure the self-organization and restructurization of these rigid-chain liquid-crystal polymers, as well as their similarity and difference. It is shown that large-scale thermal (quasi-segmental) mobility in such LC polymers is due to the reptation of macromolecules with respect to each other and the conformational transitions necessary for the motion of chains in them are the result of random accumulation of displacements that occur during local bending and torsional-vibrational movements in the links of polymer chains according to the Bresler–Frenkel mechanism.

Development of a fused-sphere SAFT-γ Mie force field for poly(vinyl alcohol) and poly(ethylene)

SAFT-γ Mie, a group-contribution equation of state rooted in Statistical Associating Fluid Theory, provides an efficient framework for developing accurate, transferable coarse-grained force fields for molecular simulation. Building on the success of SAFT-γ Mie force fields for small molecules, we address two key issues in extending the SAFT-γ Mie coarse-graining methodology to polymers: (1) the treatment of polymer chain rigidity and (2) the disparity between the structure of linear chains of tangent spheres and the structure of the real polymers. We use Boltzmann inversion to derive effective bond-stretching and angle-bending potentials mapped from all-atom oligomer molecular dynamics (MD) simulations to the coarse-grained sites and a fused-sphere version of SAFT-γ Mie as the basis for non-bonded interactions. The introduction of an overlap parameter between Mie spheres leads to a degeneracy when fitting to monomer vapor-liquid equilibria (VLE) data, which we resolve by matching polymer density from coarse-grained MD simulation with that from all-atom simulation. The result is a chain of monomers rigorously parameterized to experimental VLE data and with structural detail consistent with all-atom simulations. We test our approach on atactic poly(vinyl alcohol) and polyethylene and compare the results for SAFT-γ Mie models with structural detail mapped from the Optimized Potentials for Liquid Simulations (OPLS) and Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) all-atom force fields.

Preparation of mussel-inspired biopolyester adhesive and comparative study of effects of meta- or para-hydroxyphenylpropionic acid segments on their properties

Simple and bulk preparation of catecholic polymers is challenging. Herein, we describe a novel bio-copolyester poly(DHHCA-co-4HPPA) (polyHH4P) prepared via thermal polycondensation of renewable resources 3,4-dihydroxyhydrocinnamic acid (DHHCA) and 3-(4-hydroxyphenyl) propanoic acid (4HPPA) in one pot. PolyHH4P exhibited strong adhesion properties on diverse materials, and its adhesive strength was highly dependent on the DHHCA composition (CDHHCA). PolyHH4P with 25% CDHHCA showed the highest shear strength at fracture, with values of 10.3 MPa on carbon, 9.6 MPa on glass, and 6.2 MPa on steel substrates, and these values are higher than the corresponding values for commercial instant super glue. Furthermore, the structural effects of para-hydroxyphenylpropionic acid (para-HPPA) and meta-hydroxyphenylpropionic acid (meta-HPPA) moieties on the properties of the prepared polymers were studied. PolyHH4P with the para-HPPA moiety showed an evidently improved glass transition temperature (Tgs) relative to that of polyHH3P with meta-HPPA at the same CDHHCA, such as 19 °C increase at 25 mol% CDHHCA. However, unexpectedly, polyHH4P showed weaker adhesive shear strength than polyHH3P at the same CDHHCA mol%. We discussed the effects of CDHHCA, degree of crystallinity (CD), degree of branching (BD), catechol groups, and polymer chain rigidity on their properties. The difference in the adhesive strength of polyHH4P and polyHH3P can probably be ascribed to the higher symmetry and poorer flexibility in polyHH4P. The polyHH4P with an introduced rigid moiety and characterized by strong adhesion and an appropriately improved Tgs is expected to have potential applications in various medical fields, for example, as a dental adhesive.

Особенности локальной динамики и ориентационного состояния жесткоцепных жидкокристаллических полимеров

AbstractProton magnetic resonance (PMR) spectra and terahertz IR spectra of Vectra A950 fibers and granules and Armos fibers before and after heat treatment were obtained and analyzed in order to understand the molecular mobility mechanisms that ensure the self-organization and restructurization of these rigid-chain liquid-crystal polymers, as well as their similarity and difference. It is shown that large-scale thermal (quasi-segmental) mobility in such LC polymers is due to the reptation of macromolecules with respect to each other and the conformational transitions necessary for the motion of chains in them are the result of random accumulation of displacements that occur during local bending and torsional-vibrational movements in the links of polymer chains according to the Bresler–Frenkel mechanism.

Assessing the Huang-Brown Description of Tie Chains for Charge Transport in Conjugated Polymers.

Intercrystallite molecular connections are widely recognized to tremendously impact the macroscopic properties of semicrystalline polymers. Because it is challenging to directly probe such connections, theoretical frameworks have been developed to quantify their concentrations and predict the mechanical properties that result from these connections. Tie-chain connectivity similarly impacts the electrical properties in semicrystalline conjugated polymers. Yet, its quantitative impact has eluded the community. Here, we assess the Huang-Brown model, a framework commonly used to describe the structural origins of mechanical properties in polyolefins, to quantitatively elucidate the effect of tie chains on the electrical properties of a model conjugated polymer. We found that a critical tie-chain fraction of 10-3 is needed to support macroscopic charge transport, below which intercrystallite connectivity limits charge transport, and above which intracrystallite disorder is the bottleneck. Extending the Huang-Brown framework to conjugated polymers enables the prediction of macroscopic electrical properties based on experimentally accessible morphological parameters. Our study implicates the importance of long and rigid polymer chains for efficient charge transport over device length scales.

Fabrication of helical microfibers from melt blown polymer blends

ABSTRACTHelical fibers in micro/nanoscale resembling plant tendrils have been of increasing interest due to their unique characteristics. Fabrication of helical microfibers from polymer blends using melt blowing technique is reported in this study. An elastomeric and a stiff polymer are chosen as the raw materials, and a designed swirl‐die melt‐blowing device is used to prepare the microfibrous nonwovens. Focusing on the interfacial interaction between the polymer components induced by the polymer structure and intrinsic properties, airflow field characteristics, and processing parameters, we explore the effects of various parameters on helical fiber formation. Differential scanning calorimeter is employed to examine the rigidity of polymer chains, and the three‐dimensional airflow field simulation is carried out to reveal the airflow field characteristics. This work can provide a promising technique for producing stretchable microfibrous materials which have potential applications in field such as filtration materials and oil sorbents. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2018,56, 970–977

Rigid amorphous phase and constrained polymer chains in poly(L‐lactide) nanocomposites with carboxylated carbon nanotubes prepared via reactive melt mixing

Evaluation of constrained polymer chains and the glass transition behavior of the nanocomposite constituted by poly(L‐lactide) (PLLA) and functionalized carbon nanotubes (f‐CNTs) have been carried out. To control thermal degradation, nanocomposites were prepared via reactive melt mixing taking advantage of the capacity of carboxylic groups of both PLLA and f‐CNTs to participate in chain extension reactions. At low f‐CNT content (e.g., 0.2 and 0.5 wt%), a good dispersion of f‐CNTs was observed due to scarce bonds established between both components (i.e., the polymer matrix and the nanofiller), whereas at higher f‐CNT content (e.g., 1 wt%), a greater number of epoxy groups of the chain extender were bonded to carboxyl groups of f‐CNTs, giving rise to a highly significant crosslinking of CNT and a lower molecular weight of PLLA. Crystallinity, glass transition temperature and both the rigid polymer chains and constrained polymer chains were influenced by the dispersion state of f‐CNTs after reactive melt mixing and the thermal history (e.g., cooling rate form the melt) of samples. For evaluation of interphases between poly(lactic acid) and f‐CNTs, a simple method was developed for the considered tube‐like nanoparticles. Specifically, thicknesses of the generated interphases were calculated from DMA experiments. POLYM. COMPOS., 39:E1280–E1293, 2018. © 2018 Society of Plastics Engineers

Preparation and gas permeation of crown ether-containing co-polyimide with enhanced CO2 selectivity

In present work, crown ether-containing co-polyimide with improved gas permselectivity was developed for CO2/N2 and CO2/CH4 separation. Crown ether segment grants the co-polyimide material good affinity with CO2 as well as strong rigidity of polymer chain. This co-polyimide was prepared by the condensation polymerization and chemical imidization of 4, 4-hexafluoro-isopropylidene diphthalic anhydride, 4, 4′-diaminodiphenylmethane and trans-di(aminobenze)-18-C-6 (trans-DAB18C6). The synthesized materials were characterized by FT-IR, 1H NMR, XRD, TGA, DSC, GPC and electronic tensile machine. The fractional free volume (FFV) and fractional accessible volume (FAV) were calculated with molecular dynamics simulations. The mixed-gas permeation properties of the co-polyimide membranes were investigated to inspect the influence of trans-DAB18C6 content and feed gas pressure. Effects of testing temperature and humidity, casting solvent on membrane with 25mol% trans-DAB18C6 were investigated. The molecular dynamics simulations results showed that （FAV）CO2 decreased, while the ratios of （FAV）CO2/（FAV）N2 and （FAV）CO2/（FAV）CH4 increased progressively with trans-DAB18C6 content. The CO2 permeability increased firstly, and decreased subsequently with trans-DAB18C6 content. At the same time, both CO2/N2 and CO2/CH4 selectivities increased progressively. The co-polyimide membrane with 25mol% trans-DAB18C6 displayed the maximum CO2 permeability of 109.0 barrer and CO2/CH4 selectivity of 92.7, which surpassed the 2008 Robeson upper bound. The long term operation stability study demonstrated that the membrane had good stability.

PHYSICAL-CHEMICAL PROPERTIES OF CHONDROITIN SULFATE IN AGGRECAN

In current work theoretical study of physical-chemical properties of chondroitin sulfate in aggrecan within the self-consistent field theory was developed. As a model for aggrecan a model of cylindrical polymer brush was chosen. Aggrecan is considered as a system of n gaussian polymer chains consisting of N segments tethered to cylindrical surface of core protein. Basing on the results of previous work where using gaussian equivalent representation for functional integrals equation of state for chondroitin sulfate in aqueous solution was obtained and also osmotic pressure, dissociation degree, radius of gyration and renormalized persistent length were calculated with respect to monomers electrostatic interactions and effect of counterion condensation, one can obtain configuration integral for cylindrical polymer brush. Persistent length is introduced instead of Kuhn segment length which supposedly helps one to take into account rigidity of polymer chain determined by electrostatic repulsion of monomers (disaccharides groups). Expression for free energy of a polymer brush modeled as chondroitin sulfate chains tethered to a cylindrical surface was obtained. Dependence of chondroitin sulfate in aggrecan dissociation degree as a function of distance from the cylindrical surface is represented. For given system it varies insignificantly from the one for free chains in solution. Results for a polymer density as a function of distance from the cylindrical surface obtained within mean-field approximation are in qualitative agreement with those obtained using density functional method. However, calculations within a mean field framework are understable, thus it is necessary to use regularization methods.Forcitation:NogovitsynE.A., KalikinN.N., ZheleznyakN.I. Physical-chemical properties of chondroitin sulfate in aggrecan. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 35-39

New promising polymer for organic solvent nanofiltration: Oxidized poly (arylene sulfide sulfone)

Polymeric membranes have attracted much interest in recent years for use in organic solvent nanofiltration. This article reports the development of a novel solvent resistant oxidized poly (arylene sulfide sulfone) (PASS) membrane and proposes a new strategy to enhance the solvent resistance of this PASS membrane via improving the rigidity, intermolecular interaction and packing density of polymer chains by a simple oxidation process. The PASS membranes were firstly fabricated by phase inversion, and then a facile green oxidation process was carried out to improve their solvent resistance. The oxidized PASS (O-PASS) membrane was found to exhibit an excellent stability in aggressive solvents, such as DMF and NMP, and endure 98% H2SO4 without sacrificing its filtration performance. In organic solvent nanofiltration (OSN), the O-PASS membranes exhibited a high rejection of dyes such as rose Bengal (RB), erythrosin B (EB), reactive orange 16 (RB16) and Sudan black B (SBB), and a stable filtration performance for 30h in DMF. Compared to other reported OSN membranes, this membrane showed an exceptionally high solvent permeation. This extraordinary OSN filtration performance, easy fabrication process and the strong solvent resistance, make PASS a very promising polymer in the field of OSN.

Effect of diamond blend on the gas-separation properties of composite membranes

The morphological structure and gas transport properties of polyimide- and polyamide-imidebased rigid-chain polymers containing a fine carbon filler (a diamond blend) are studied. Gas transport properties are measured, and the effect exerted on these properties by intermolecular interaction between the functional groups of polymer chains and the fine filler is analyzed.

Rigid biphenyl-contained epoxy resins with improved thermal resistant properties

Biphenyl-contained monomer of 1,4-bis[2-(3,4-epoxy cyclohexyl ethyl) dimethylsilyl] biphenyl (BP-SiH-EP) was prepared via hydrosilylation reaction of 1,4-bis(dimethylsilyl) biphenyl (BP-SiH) and 1,2-epoxy-4-vinylcyclohexane in the presence of Karstedt’s catalyst. 1H-NMR, 13C-NMR and FTIR were used to characterize the structure of the obtained monomer. BP-SiH-EP was then cured by methyl hexahydrophthalic anhydride (MeHHPA) with 1-cyanoethyl-2-ethyl-4-methylimidazole as an accelerator. The polymerization behavior was studied by DSC. The results of DMA measurement demonstrate that the cured BP-SiH-EP/MeHHPA can maintain high storage modulus (> 1 GPa) in a wide range of temperature up to 176 °C. According to the damping factor curve of DMA, cured BP-SiH-EP/MeHHPA exhibits a high glass transition temperature (T g) of 192 °C, which is 20 °C higher than that of cured 1,4-bis[2-(3,4-epoxy cyclohexyl ethyl) dimethylsilyl] benzene (DEDSB)/MeHHPA. TGA results show that cured BP-SiH-EP/MeHHPA has good thermal stability (T 5% = 339 °C) due to the high heat-resistance of rigid biphenyl group. Moreover, the crosslinking density of cured BP-SiH-EP/MeHHPA should be lower than that of cured DEDSB/MeHHPA estimated from their chemical structures, which conflicts with the calculated results based on the rubber elasticity equation. The inconsistence indicates that the calculated crosslinking densities are not comparable, possibly owing to their differences in the rigidity of polymer chains and intermolecular interaction.

Preparation and optical properties of composite materials based on polybenzimidazole and silver nanoparticles

Rigid-chain heat resistant polymers (with poly-2,2'-p-oxydiphenylene-5,5′-bisbenzimidazole as example) were impregnated for the first time with a silver-containing precursor in formic acid and in supercritical carbon dioxide. A procedure allowing the precursor reduction to silver nanoparticles both throughout the volume by thermal annealing of the films in the temperature interval 100–150°С and in the targeted mode using lasers operating at 405 and 532 nm was developed. It opens prospects for developing a process for production of heatresistant optical gratings and light guides. The reduces nanoparticles and their agglomerates have the size in the interval 50–200 nm and give a plasmon band in the range 450–460 nm.