Linear Polymer Chains Research Articles

Nanostructure-Dependent Antimicrobiotic Activity and Selectivity of Synthetic Membrane-Active Polymers

Antibiotic resistance has become one of the greatest challenges in treating bacterial infections in healthcare. Inspired by the structures of bacteria-invading viruses and antimicrobial peptides (AMPs), we hypothesize that in addition to a balance of amphiphilicity and electropositivity, nanostructure is another important structural determinant that defines how membrane-active antibiotics remodel host membranes to gain desirable activity and selectivity. Here we study the structure-activity relationship of a series of polymer molecular brushes (PMBs) with well-defined nanostructures that mimic spherical and rod-shaped viruses. Our preliminary data based on PMBs with hydrophilic polymer brushes reveal that: (1) amphiphilicity is not a required trait - hydrophilic PMBs can be designed to have potent antibiotic performance as well with negligible hemolytic activity; (2) the nanoscale architecture of PMBs defines their double selectivity, not molecular weight per se; (3) PMBs are far more powerful antibiotics than individual linear-chain polymers that make up the PMBs; and (4) nanostructured PMBs induce topological changes of membranes by forming membrane pores that unlikely fit in with any known models of AMP action. These findings expand existing wisdom on designing synthetic mimics of AMPs and suggest that the spatially-defined, multivalent interactions inherent to nanostructured PMBs is of great significance for the development of new membrane-active antibiotics.

Density effects in entangled solutions of linear and ring polymers

In this paper, we employ molecular dynamics computer simulations to study and compare the statics and dynamics of linear and circular (ring) polymer chains in entangled solutions of different densities. While we confirm that linear chain conformations obey Gaussian statistics at all densities, rings tend to crumple becoming more and more compact as the density increases. Conversely, contact frequencies between chain monomers are shown to depend on solution density for both chain topologies. The relaxation of chains at equilibrium is also shown to depend on topology, with ring polymers relaxing faster than their linear counterparts. Finally, we discuss the local viscoelastic properties of the solutions by showing that the diffusion of dispersed colloid-like particles is markedly faster in the rings case.

Novel magneto-responsive membrane for remote control switchable molecular sieving.

Stimuli-responsive separation membranes with tunable molecular scale pore size, which are desirable for on-demand sieving of targeted macromolecules, have attracted increasing attention in recent years. In this study, novel magneto-hydrogel pore-filled composite membranes with excellent magneto-responsivity and tunability for molecular sieving have been developed. Such membranes comprising magnetic nanoparticles (MNPs) as localized heater which can be excited by high frequency alternating magnetic field (AMF), poly(N-isopropylacrylamide) (PNIPAAm) hydrogel network as the sieving medium and actuator, and polyethylene terephthalate (PET) track-etched membrane as robust support, have been prepared via in situ reactive pore-filling functionalization. Rheological study has been carried out first to investigate the influence of MNPs and initiation methods on gelation kinetics and microstructure of the MNP-PNIPAAm composite hydrogels, and to identify proper conditions for further pore-filling functionalization. Then AMF distribution of chosen field condition and its heating effectiveness for MNPs and MNP-PNIPAMm composite hydrogel were studied. Pre-functionalization of the PET membranes with linear polymer chains with different composition were compared with respect to their effects for achieving desired MNP loading and fixation of the hydrogel network in the pores. At last, in situ reactive pore-filling functionalization was carried out to immobilize robust magneto-hydrogel in the pores of the membranes. Conditions were investigated and optimized to obtain functionalized membranes with high MNP loading and suited PNIPAM network properties, i.e. good stimuli-responsivity and sieving in the ultrafiltration range. The excellent thermo- and magneto-responsivity of obtained pore-filled membranes was proved by its large and reversible change of water permeability in response to switching on and off the AMF. Finally, it was demonstrated by filtration of dextrans with different molecular weights that the membranes had ultrafiltration properties and that large changes of their molecular sieving performance could be obtained by "remote control" with the external AMF.

Precise grafting of macrocyclics and dendrons to a linear polymer chain

Sequential growth of multifunctional telechelic polymer chains allowing grafting of polymeric dendrons and cyclics equally spaced along the backbone.

Influence of Confinement on the Chain Conformation of Cyclic Poly(N-isopropylacrylamide).

In thin and ultrathin supported films, the conformations of flexible linear polymer chains might be considerably confined, in particular, for film thicknesses smaller than a few times the radius of gyration. For ring polymers in solution or in melt, the radii of gyration are significantly reduced as compared to those of their linear counterparts. We study here the influence of geometrical confinement on the chain conformation of cyclic PNIPAM in silicon-supported films. Measurements are performed by grazing incidence small angle neutron scattering (GISANS). For all films, the component of the radius of gyration parallel to the substrate, Rgc∥, is significantly higher than the unperturbed Rgc determined under theta solvent or melt conditions. We attribute this effect to a preferential selection of stretched PNIPAM ring conformations in thin films and a preferential orientation of macromolecules parallel to the film interfaces with the substrate and air.

The Role of Nanoparticle Rigidity on the Diffusion of Linear Polystyrene in a Polymer Nanocomposite

The impact of the inclusion of a nanoparticle in a polymer matrix on the dynamics of the polymer chains is an area of recent interest. In this article, we describe the role of nanoparticle rigidity or softness on the impact of the presence of that nanoparticle on the diffusive behavior of linear polymer chains. The neutron reflectivity results clearly show that the inclusion of ∼10 nm soft nanoparticles in a polymer matrix (Rg ∼ 20 nm) increases the diffusion coefficient of the linear polymer chain. Surprisingly, thermal analysis shows that these nanocomposites exhibit an increase in their glass transition temperature, which is incommensurate with an increase in free volume. Therefore, it appears that this effect is more complex than a simple plasticizing effect. Results from small-angle neutron scattering of the nanoparticles in solution show a structure that consists of a gel like core with a corona of free chain ends and loops. Therefore, the increase in linear polymer diffusion may be related to an in...

Efficient fabrication of polymer nanoparticles via sonogashira cross‐linking of linear polymers in dilute solution

ABSTRACTThe synthesis of single‐chain nanoparticles by palladium‐catalyzed Sonogashira coupling between a terminal alkyne and a di‐halo aryl cross‐linker is reported. Statistical copolymers with trimethylsilyl protected alkyne groups pendent to the linear methacrylate back bones were synthesized using reversible addition‐fragmentation chain transfer polymerization post polymerization de‐protection providing terminal alkyne functionalized linear polymer chains. These linear polymer chains were intramolecularly cross‐linked via bifunctional cross‐linkers. The resulting well‐defined covalently bonded nanoparticles were characterized via triple‐detection size exclusion chromatography where MALS detector provided molecular weight information and viscometric detection characterizes particle size and conformations. The particle size could be readily tuned through polymer molecular weight and by degree of cross‐linking. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 209–217

Relaxation Process of Linear Polymer Chain in Post Array

We present an extensive set of simulation results for the relaxation processes of linear polymer chains embedded in post arrays using Monte Carlo algorithm. The comparison of different end-to-end relaxation functions shows that polymer chains exhibit reptation in post arrays. The relaxation is almost pure reptation for small array spacing while contour length fluctuation plays a role for large array spacing.

Communication: When does a branched polymer become a particle?

Polymer melts with topologically distinct molecular structures, namely, linear chain, ring, and star polymers, are investigated by molecular dynamics simulation. In particular, we determine the mean polymer size and shape, and glass transition temperature for each molecular topology. Both in terms of structure and dynamics, unknotted ring polymers behave similarly to star polymers with f ≈ 5-6 star arms, close to a configurational transition point between anisotropic chains to spherically symmetric particle-like structures. These counter-intuitive findings raise fundamental questions regarding the importance of free chain-ends and chain topology in the packing and dynamics of polymeric materials.

Brushing up on being soft and squishy

Materials Science Polymer gels can be thought of as a netlike structure of cross-linked linear polymer chains swollen with solvent. Because these materials are mostly liquid, they can be quite soft and squishy, but this means that solvent loss, which makes the gels sticky, also is a concern. Cai et

Polymer films of nanoscale thickness: linear chain and star-shaped macromolecular architectures

Abstract

Local response in nanopores

In this work the transient time correlation function (TTCF) algorithm is applied to study highly confined molecular fluids. We focus on linear polymer chains of various lengths trapped in a slab pore which is a few nanometres thick and made of atomistic walls, and the behaviour and response of the polymer melt subject to shear flow are considered. The shearing is produced by shifting the walls in opposite directions, and the temperature inside the channel is controlled by a thermostat applied to the wall atoms alone, so as to mimic the dissipation of heat as it occurs in real devices. It is shown how the TTCF algorithm can be applied to extract the fluid's dynamical and structural properties as they evolve from equilibrium and until a steady state has been established. We note that this procedure is applicable to fluids of any complexity and down to extremely low fields, comparable to those present in experimental devices. It is also shown that this technique can be used to probe local properties at specific locations across the channel. This feature is of particular significance because liquid properties inside nanoconfined geometries are mostly determined by the interactions at the interface and specifically by the structural reordering which affects the first few atomic/molecular layers close to the wall surface, e.g. slip.

Template Synthesis of Linear‐Chain Nanodiamonds Inside Carbon Nanotubes from Bridgehead‐Halogenated Diamantane Precursors

AbstractA simple method for the synthesis of linear‐chain diamond‐like nanomaterials, so‐called diamantane polymers, is described. This synthetic approach is primarily based on a template reaction of dihalogen‐substituted diamantane precursors in the hollow cavities of carbon nanotubes. Under high vacuum and in the presence of Fe nanocatalyst particles, the dehalogenated radical intermediates spontaneously form linear polymer chains within the carbon nanotubes. Transmission electron microscopy reveals the formation of well‐aligned linear polymers. We expect that the present template‐based approach will enable the synthesis of a diverse range of linear‐chain polymers by choosing various precursor molecules. The present technique may offer a new strategy for the design and synthesis of one‐dimensional nanomaterials.

Template Synthesis of Linear-Chain Nanodiamonds Inside Carbon Nanotubes from Bridgehead-Halogenated Diamantane Precursors.

A simple method for the synthesis of linear-chain diamond-like nanomaterials, so-called diamantane polymers, is described. This synthetic approach is primarily based on a template reaction of dihalogen-substituted diamantane precursors in the hollow cavities of carbon nanotubes. Under high vacuum and in the presence of Fe nanocatalyst particles, the dehalogenated radical intermediates spontaneously form linear polymer chains within the carbon nanotubes. Transmission electron microscopy reveals the formation of well-aligned linear polymers. We expect that the present template-based approach will enable the synthesis of a diverse range of linear-chain polymers by choosing various precursor molecules. The present technique may offer a new strategy for the design and synthesis of one-dimensional nanomaterials.

A Finsler Geometry Modeling of the Liquid Crystal Elastomer

Liquid crystal elastomer (LCE) is a rubbery material composed of polymer chains and liquid crystals (LC). LCE is well known to undergo a shape transformation from the isotropic to the anisotropic phase. This shape transformation is caused by the nematic transition of the LC included in the LCE. However, the mechanism of this transformation is unknown because the interaction of LC with the bulk polymers is too complex. In this presentation, we extend the two-dimensional Finsler geometry model for membranes to a three-dimensional model for LCE. The Finsler geometry model for LCE is a coarse grained one: the Guassian bond potential S1 is obtained by extending the one for membranes, which is originally obtained by a simple extension of the Guassian bond potential for the linear chain polymer model. The continuous Hamiltonian, which contains S1 and the curvature energy S2, is discretized using a three-dimensional rigid sphere composed of tetrahedrons. We study the shape transformation as a phase transition between the isotropic and anisotropic phases and report the results of the transition order, obtained by the Monte Carlo simulations.

Redox/pH stimuli-responsive biodegradable PEGylated P(MAA/BACy) nanohydrogels for controlled releasing of anticancer drugs

Abstract Stimuli responsive drug delivery systems have attracted considerable attention due to their ability to deliver drugs on demand to special tissues and cells (e.g. cancer cells). In this paper, we fabricated a new kind of redox/pH dual stimuli-responsive biodegradable poly(methacrylic acid) (MAA) nanohydrogels crosslinked by N,N-bis(acryloyl)cystamine (BACy) through a facile reflux-precipitation polymerization. Subsequently polyethylene glycol (PEG) was grafted onto the surface of nanohydrogels to improve their long circulation time. This kind of PEGylated nanohydrogels could be degraded into short linear polymer chains in the solution of 10 mM glutathione (GSH) due to the sensitive disulfide bonds in the cross-linked networks. Interestingly, we found that the hydrophilic PEGylated nanohydrogels could be simultaneously loaded with hydrophilic drug doxorubicin (DOX) and hydrophobic drug paclitaxel (PTX) with high drug loading efficiency because of its regional hydrophobic nature in the nanohydrogels. The cumulative release profile showed that either lower pH (5.0) or reducing environment (GSH) or a combination could significantly accelerate the drug release from the drug-loaded nanohydrogels. In addition, the experimental results on living cells indicated that the multi-drug-loaded system had synergistic effect on cancer therapy.

Study on the effects of isotropic cross-linked pristine morphology and electro-optical properties of PDLC films

PDLC films were prepared by polymerization-induced phase separation (PIPS) method along with varying composition ratio between curable epoxy monomers/poly-oxy-propylene-di-amine (POPDA) cross-linking agent/Class α, longitudinal nematic liquid crystal (LC) linear chain polymer mixtures and their optical and pristine morphological properties have been analyzed to investigate their suitability as aligned nematic phase of LC. The refractive index of isotropic cross-linked polymer network could be influenced by the relative content of curable monomers structure PPGDE ~380 and PPGDE ~640 which increased the LC droplet size with POPDA. Meanwhile, it is examined that the decreasing of peel strength and transmittance of all the samples decrease of wavelength in the wavelength range of 300–800 nm due to the lower cross-linking density of the polymer network with effect of strongly influenced by the alkoxy (R-O) and flexible chain length of curable monomers, which also affect the electro-optical properties and droplet size of LC in PDLC films. Our results demonstrate that the LC droplet size of the isotropic cross-linked polymer network could be regulated by adjusting the monomers structure, composition ratio, relative wt% of POPDA, PPGDE ~380 and PPGDE ~640; then aligned nematic phase of LC have the optical properties of uniaxial crystals and their potential applications for PDLC smart glass market and display fields.

Synthesis and structure of coordination polymers of praseodymium(III) and erbium(III) with hydrogen maleate and benzene-1,3-disulfonate as linkers

Two new 1D coordination polymers [Pr(1,3-BDS)(HMA)(H2O)4] n and [Er(1,3-BDS)(HMA)(H2O)4] n (1,3-BDS = benzene-1,3-disulfonate and H2MA = maleic acid) having one-dimensional zigzag polymeric structure and containing praseodymium and erbium in +3 oxidation state were synthesized by solution synthesis method. The compositions and structures of coordination polymers were determined by elemental analysis, FT-IR, X-ray diffraction, and results of thermal decomposition. Coordination polymers [Pr(1,3-BDS)(HMA)(H2O)4] n and [Er(1,3-BDS)(HMA)(H2O)4] n are isomorphous and contain distorted square antiprism geometry around metal ion. Two molecules of benzene-1,3-disulfonate and hydrogen maleate coordinate to each metal ion in unidentate bridging mode to generate a linear zigzag polymeric chain. Four water molecules are also coordinated to each metal ion. Hydrogen bonded interaction involving water molecules, carboxylate and sulfonate groups of adjacent polymer chains lead to two-dimensional polymer expansion. The polymers are thermally robust as is indicated by thermal studies.

A novel poly(acrylic acid-co-acrylamide)/diatomite composite flocculant with outstanding flocculation performance.

Series of anionic flocculants with outstanding flocculation performance, poly(acrylic acid-co-acrylamide)/diatomite composite flocculants (PAAD) were successfully prepared through aqueous solution copolymerization and applied to flocculate from oil-field fracturing waste-water. The structure of PAAD was characterized by Fourier transform infra-red spectroscopy, (13)C nuclear magnetic resonance and X-ray diffraction tests, and its properties were systematically evaluated by viscometer, thermogravimetry analysis and flocculation measurements. Furthermore, the influences of various reaction parameters on the apparent viscosity of flocculant solution were studied, and the optimum synthesis condition was determined. The novel composite flocculants exhibited outstanding flocculation properties. Specifically, the dosage of composite flocculants that could make the transmittance of treated wastewater exceed 90% was only approximately 12-35 ppm, which was far lower than that of conventional flocculants. Meanwhile, the settling time was lower than 5 s, which was similar to that of conventional flocculants. This was because PAAD flocculants had a higher absorption capacity, and larger chain extending space than conventional linear flocculants, which could refrain from the entanglement of linear polymer chains and significantly improve flocculation capacity.

Biofunctionalizable flexible bucky paper by combination of multi-walled carbon nanotubes and polynorbornene-pyrene – Application to the bioelectrocatalytic reduction of oxygen

Owing to their conductivity, carbon nanotubes (CNTs) coatings are widely used for modifying electrode surfaces. In particular, the formation of bucky papers (BP) based on CNT assemblies obtained by filtration, represents an attractive way of creating a new kind of electrode. However, these BP are brittle and difficult to manipulate, hence their applications remain limited due to their fragility and lack of flexibility. Notably, their use for “in vivo” experiments is markedly hampered by the potential release of CNTs. The strengthening of the mechanical stability of BP has hereby been explored by the combination of BP and linear polymeric chains displaying non-covalent π-interactions with CNTs. These organic polymers act as a cross-linking agent throughout the BP assembly thus conferring stability and flexibility. Flexible BP electrodes were produced by simply mixing poly(norbornene) bearing pyrene groups and multi-walled CNTs, both dispersed in dimethylformamide followed by filtration through a PTFE membrane. The immobilization of laccase as a model protein was achieved on the resulting BP electrodes by adsorption or chemical grafting. These biocathodes displayed a direct electrical communication with laccase, allowing the reduction of oxygen in water (pH 5) with maximum current densities of ca 1.1mAcm−2 at 0.4V vs. SCE.