Single Copolymer Research Articles

On the rupture of DNA molecule.

Using Langevin dynamics simulations, we study effects of the shear force on the rupture of a double stranded DNA molecule. The model studied here contains two single diblock copolymers interacting with each other. The elastic constants of individual segments of diblock copolymer are considered to be different. We showed that the magnitude of the rupture force depends on whether the force is applied at 3' - 3' - ends or 5' - 5' - ends. Distributions of extension in hydrogen bonds and covalent bonds along the chain show the striking differences. Motivated by recent experiments, we have also calculated the variation of rupture force for different chain lengths. Results obtained from simulations have been validated with the analytical calculation based on the ladder model of DNA.

Effects of collagen incorporation on thermogelation and hydrogel characteristics of aqueous Pluronic F127 copolymer system

As one of the most widely used thermosensitive polymers, commercially available Pluronic F127 copolymer has been used as an attractive candidate for injectable hydrogel system. To tune its characteristics for better biomedical applications, the effects of collagen incorporation on its thermogelation in aqueous system and resultant hydrogel properties were investigated by dynamic rheological tests, scanning electron microscopic observation, in vitro drug release, and cytocompatibility assays. For its aqueous solution, the collagen incorporation was found to improve appropriately the sol–gel transition temperature for good injectability at room temperature and enhance obviously the temperature sensitivity for fast thermogelation. When compared to single Pluronic F127 copolymer thermogel, the composite thermogel with collagen showed a prolonged release for encapsulated drug and better cell compatibility. In addition, the effects on the morphology and viscoelastic behavior of resultant thermogel were also studied with respect to the concentration of incorporated collagen.

Widely Tunable Morphologies in Block Copolymer Thin Films Through Solvent Vapor Annealing Using Mixtures of Selective Solvents.

Thin films of block copolymers are extremely attractive for nanofabrication because of their ability to form uniform and periodic nanoscale structures by microphase separation. One shortcoming of this approach is that to date the design of a desired equilibrium structure requires synthesis of a block copolymer de novo within the corresponding volume ratio of the blocks. In this work, we investigated solvent vapor annealing in supported thin films of poly(2-hydroxyethyl methacrylate)-block-poly(methyl methacrylate) [PHEMA-b-PMMA] by means of grazing incidence small angle X-ray scattering (GISAXS). A spin-coated thin film of lamellar block copolymer was solvent vapor annealed to induce microphase separation and improve the long-range order of the self-assembled pattern. Annealing in a mixture of solvent vapors using a controlled volume ratio of solvents (methanol, MeOH, and tetrahydrofuran, THF), which are chosen to be preferential for each block, enabled selective formation of ordered lamellae, gyroid, hexagonal or spherical morphologies from a single block copolymer with a fixed volume fraction. The selected microstructure was then kinetically trapped in the dry film by rapid drying. To our knowledge, this paper describes the first reported case where in-situ methods are used to study the transition of block copolymer films from one initial disordered morphology to four different ordered morphologies, covering much of the theoretical diblock copolymer phase diagram.

Reproducible Access to Tunable Morphologies via the Self-Assembly of an Amphiphilic Diblock Copolymer in Water

We report on the preparation of positively charged crew-cut nanoaggregates in water with various nonspherical (i.e., worm, flower, and large compound) and spherical (i.e., vesicle and sphere) morphologies by the self-assembly of a single diblock copolymer in water. Our facile procedure for preparing positively charged nanoparticles, when combined with the techniques for obtaining negatively charged and neutral nanoaggregates already established by Eisenberg et al., provides a versatile toolbox for the reproducible production of uniformly nanostructured particles with control over both morphology and surface chemistry. Such nanoparticles offer opportunities for the fundamental study of nanobio interactions and may open the door to novel drug and gene delivery applications.

Single chain structure of a poly(N-isopropylacrylamide) surfactant in water.

We present atomistic simulations of a single PNIPAM-alkyl copolymer surfactant in aqueous solution at temperatures below and above the LCST of PNIPAM. We compare properties of the surfactant with pure PNIPAM oligomers of similar lengths, such as the radius of gyration and solvent accessible surface area, to determine the differences in their structures and transition behavior. We also explore changes in polymer-polymer and polymer-water interactions, including hydrogen bond formation. The expected behavior is observed in the pure PNIPAM oligomers, where the backbone folds onto itself above the LCST in order to shield the hydrophobic groups from water. The surfactant, on the other hand, does not show much conformational change as a function of temperature, but instead folds to bring the hydrophobic alkyl tail and PNIPAM headgroup together at all temperatures. The atomic detail available from these simulations offers important insight into understanding how the transition behavior is changed in PNIPAM-based systems.

Single component thermo-gelling electroactive hydrogels from poly(caprolactone)-poly(ethylene glycol)-poly(caprolactone)-graft-aniline tetramer amphiphilic copolymers.

Injectable biodegradable and conductive hydrogels have great potential applications in the regeneration of soft tissues sensitive to electrical signals. Herein, we have developed a series of injectable conductive hydrogels using a single component copolymer poly(caprolactone)-poly(ethylene glycol)-poly(caprolactone) (PCEC) grafted aniline tetramer (AT) via a thermo-gelling approach. The chemical structure, thermal property, and electrochemical property of the amphiphilic copolymer PCEC-AT, and the multi-interactions, morphologies, swelling ratio, dynamic mechanical property, and gelation time of the hydrogels from PCEC-AT were characterized. Injectability of the in situ forming electroactive hydrogels was verified by in vivo subcutaneous injection into a Sprague-Dawley rat. The cytotoxicity of the PCEC-AT conductive copolymers was evaluated by culturing C2C12 myoblasts with the copolymers, and all the samples showed no cytotoxicity, suggesting the good cytocompatibility of the injectable hydrogels. These injectable biodegradable and conductive hydrogels with good biocompatibility are promising candidates for the repair of soft tissues where electrical signals are needed.

Synthesis and properties of stereo mixtures of enantiomeric block copolymers of polylactide and aliphatic polycarbonate

AbstractABA triblock copolymers of polylactides (PLA: A) and aliphatic polycarbonates (APC: B) were prepared by ring‐opening polymerization of d‐ and l‐lactides with poly(hexamethylene carbonate) diol and poly(hexamethylene/pentamethylene carbonate) diol (PHPC) as macro‐initiators. The enantiomeric copolymers with similar block sequences (PLLA‐APC‐PLLA and PDLA‐APC‐PDLA) were mixed in a 1:1 weight ratio to form a stereocomplex of PLA blocks. The resultant stereo mixtures were found to be more thermally stable (up to 200 °C) than the single block copolymers. Polymer films of the stereo mixtures PLLA‐PHPC‐PLLA/PDLA‐PHPC‐PDLA exhibited higher elongation and lower modulus. It was therefore evident that the present enantiomeric block copolymer system can be applicable as a novel thermoplastic elastomer that is environmentally friendly in terms of its biobased nature and the use of carbon dioxide as feedstock. © 2014 Society of Chemical Industry

Block copolymer/homopolymer dual-layer hollow fiber membranes

We manufactured the first time block copolymer dual-layer hollow fiber membranes and dual layer flat sheet membranes manufactured by double solution casting and phase inversion in water. The support porous layer was based on polystyrene and the selective layer with isopores was formed by micelle assembly of polystyrene-b-poly-4-vinyl pyridine. The dual layers had an excellent interfacial adhesion and pore interconnectivity. The dual membranes showed pH response behavior like single layer block copolymer membranes with a low flux for pH values less than 3, a fast increase between pH4 and pH6 and a constant high flux level for pH values above 7. The dry/wet spinning process was optimized to produce dual layer hollow fiber membranes with polystyrene internal support layer and a shell block copolymer selective layer.

Phase Behavior of a Single Structured Ionomer Chain in Solution

Structured polymers offer a means to tailor transport pathways within mechanically stable manifolds. The building block of such a membrane is examined, namely a single large pentablock co-polymer that consists of a center block of a randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability, using molecular dynamics simulations. The polymer structure in a cyclohexane-heptane mixture, a technologically viable solvent, and in water, a poor solvent for all segments and a ubiquitous substance is extracted. In all solvents the pentablock collapsed into nearly spherical aggregates where the ionic block is segregated. In hydrophobic solvents, the ionic block resides in the center, surrounded by swollen intermix of flexible and end blocks. In water all blocks are collapsed with the sulfonated block residing on the surface. Our results demonstrate that solvents drive different local nano-segregation, providing a gateway to assemble membranes with controlled topology.

Collapse transitions in thermosensitive multi-block copolymers: a Monte Carlo study.

Monte Carlo simulations are performed on a simple cubic lattice to investigate the behavior of a single linear multiblock copolymer chain of various lengths N. The chain of type (AnBn)m consists of alternating A and B blocks, where A are solvophilic and B are solvophobic and N = 2nm. The conformations are classified in five cases of globule formation by the solvophobic blocks of the chain. The dependence of globule characteristics on the molecular weight and on the number of blocks, which participate in their formation, is examined. The focus is on relative high molecular weight blocks (i.e., N in the range of 500-5000 units) and very differing energetic conditions for the two blocks (very good-almost athermal solvent for A and bad solvent for B). A rich phase behavior is observed as a result of the alternating architecture of the multiblock copolymer chain. We trust that thermodynamic equilibrium has been reached for chains of N up to 2000 units; however, for longer chains kinetic entrapments are observed. The comparison among equivalent globules consisting of different number of B-blocks shows that the more the solvophobic blocks constituting the globule the bigger its radius of gyration and the looser its structure. Comparisons between globules formed by the solvophobic blocks of the multiblock copolymer chain and their homopolymer analogs highlight the important role of the solvophilic A-blocks.

Intramolecular structures in a single copolymer chain consisting of flexible and semiflexible blocks: Monte Carlo simulation of a lattice model

We study conformational properties of a single multiblock copolymer chain consisting of flexible and semiflexible blocks. Monomer units of different blocks are equivalent in the sense of the volume interaction potential, but the intramolecular bending potential between successive bonds along the chain is different. We consider a single flexible-semiflexible regular multiblock copolymer chain with equal content of flexible and semiflexible units and vary the length of the blocks and the stiffness parameter. We perform flat histogram type Monte Carlo simulations based on the Wang-Landau approach and employ the bond fluctuation lattice model. We present here our data on different non-trivial globular morphologies which we have obtained in our model for different values of the block length and the stiffness parameter. We demonstrate that the collapse can occur in one or in two stages depending on the values of both these parameters and discuss the role of the inhomogeneity of intraglobular distributions of monomer units of both flexible and semiflexible blocks. For short block length and/or large stiffness the collapse occurs in two stages, because it goes through intermediate (meta-)stable structures, like a dumbbell shaped conformation. In such conformations the semiflexible blocks form a cylinder-like core, and the flexible blocks form two domains at both ends of such a cylinder. For long block length and/or small stiffness the collapse occurs in one stage, and in typical conformations the flexible blocks form a spherical core of a globule while the semiflexible blocks are located on the surface and wrap around this core.

Experimental study and modeling of nanofoams formation from single phase acrylic copolymers

Medium to low density thermoplastic nanofoams have previously been produced using nanoparticles as nucleating center. Here we show that by designing the molecular structure of the polymer matrix to achieve high CO2 solubility while controlling the glass transition temperature, it is possible to produce nanofoams with cell nucleation densities as high as 1016/cm3 without introducing nucleation aids. This was achieved by maximizing foam expansion without uncontrolled cell ripening for a series of acrylic copolymers, which were foamed under a set of standard conditions. To predict the role of foaming conditions on foam characteristics, a theoretical foaming model was built to simulate cell nucleation, growth and foam stabilization. Experimental or predicted properties of the polymer/carbon dioxide mixture were used as inputs. Despite simplifying assumptions, such as the use of classical nucleation equations, the semi-quantitative model provides insight into the foam expansion behavior and validates experimental observations.

Preparation and behavior of “molecular compound” through covalent crosslinking between amino and sulfonic groups in single copolymers

4-Aminophenyl hydroquinone (4Am-PH), a bisphenol monomer, was synthesized and further reacted with bisphenol A (in three different molar ratios), 3.3′-disulfonated 4.4′-dichlorodiphenyl sulfone, and 4.4′-difluorobenzophenone to prepare three sulfonated poly(arylene ether ketone sulfone) copolymers with different amounts of pendant amino groups (Am-SPAEKS-1, Am-SPAEKS-2, and Am-SPAEKS-3), while the molar ratio of 3.3′-disulfonated-4.4′-diphenyl sulfone to 4.4′-difluoro diphenylmethanone was kept constant. Three crosslinked polymeric membranes (C–Am-SPAEKS-1, C–Am-SPAEKS-2, and C–Am-SPAEKS-3) with a varying degree of crosslinking were prepared by heating the corresponding Am-SPAEKS copolymers at 180 °C. 4Am-PH, Am-SPAEKS copolymers, and C-Am-SPAEKS membranes were characterized by Fourier transform infrared and 1H NMR spectroscopy. Compared to non-crosslinked membranes, some properties of the crosslinked membranes are obviously improved, such as dimensional stability, oxidative stability, methanol resistance capacity and mechanical stability. The proton conductivity of C-Am-SPAEKS-2 membrane reaches a value of 0.089 S cm−1, which is higher than those of SPAEKS and Am-SPAEKS-2 at 120 °C. These results indicate the C-Am-SPAEKS crosslinked polymeric membranes are suitable candidate for applications in proton exchange membrane fuel cells.

Effect of Basicity of Amino Group at Side Chain in Diallylamine-Type Copolymer Additive on Via-Filling by Copper Electrodeposition

We achieved the bottom-up via-filling by copper electrodeposition using a single diallylamine-type copolymer additive instead of the four types of additives, Suppressor Leveler Accelerator and Chloride ions. We newly synthesized and used four additives modified side chains to research more the function of this additive. We observed vias cross sections, performed an electrochemical analysis and conducted quartz crystal microbalance (QCM) measurements. By comparing the amino group at the end of the side chain with the one near the main chain, it was found the basicity of the latter is weak due to the neighboring group effect. However, when the distance between these two amino groups is long, the basicity of the amino group near the main chain is strong. The use of a polymer additive with a strong amino group near the main chain had the effect of suppressing the electrodeposition outside vias and achieving a good bottom-up filling.

Effects of Cationic Ammonium Gemini Surfactant on Micellization of PEO–PPO–PEO Triblock Copolymers in Aqueous Solution

Effects of cationic ammonium gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12) on the micellization of two triblock copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), F127 (EO97PO69EO97) and P123 (EO20PO70EO20), have been studied in aqueous solution by differential scanning calorimetry (DSC), dynamic light scattering (DLS), isothermal titration calorimetry (ITC), and NMR techniques. Compared with traditional single-chain ionic surfactants, 12-6-12 has a stronger ability of lowering the CMT of the copolymers, which should be attributed to the stronger aggregation ability and lower critical micelle concentration of 12-6-12. The critical micelle temperature (CMT) of the two copolymers decreases as the 12-6-12 concentration increases and the ability of 12-6-12 in lowering the CMT of F127 is slightly stronger than that of P123. Moreover, a combination of ITC and DLS has shown that 12-6-12 binds to the copolymers at the temperatures from 16 to 40 °C. At the temperatures below the CMT of the copolymers, 12-6-12 micelles bind on single copolymer chains and induce the copolymers to initiate aggregation at very low 12-6-12 concentration. At the temperatures above the CMT of the copolymers, the interaction of 12-6-12 with both monomeric and micellar copolymers leads to the formation of the mixed copolymer/12-6-12 micelles, then the mixed micelles break into smaller mixed micelles, and finally free 12-6-12 micelles form with the increase of the 12-6-12 concentration.

Pronounced synergistic influence of mixed substrate cultivation on single step copolymer P(3HB-co-4HB) biosynthesis with a wide range of 4HB monomer composition

BACKGROUND Copolymer poly(3-hydroxybutyrate-co-4-hydroxybutyrate), P(3HB-co-4HB) has gained importance in biotechnological processes due to its potential as an absorbable material in biopharmaceutical applications. The aim of the present study was to investigate the implementation of mixed substrate cultivation concept in single step production of copolymer P(3HB-co-4HB). Evaluation of the sole carbon sources was first carried out to elucidate the difference in the monomer content of 4HB using different types and concentrations of carbon sources. This is followed by the study of mixed-substrate cultivation on copolymer biosynthesis. Finally, the molecular weight of copolymers with various 4HB monomer compositions was also determined. RESULTS Experimentation using the sole carbon source recorded the highest PHA content, PHA concentration and 4HB monomer composition of 57 wt%, 3.1 g L−1 and 48 mol%, respectively. Manipulation of the carbon source combination showed the synergistic influence of the substrates mixture towards single-stage production of P(3HB-co-4HB), which enhanced the yield of copolymer P(3HB-co-4HB), to a maximum PHA content and concentration of 74 wt% and 6.9 g L−1. In addition, 4HB monomer composition up to a maximum of 70 mol% was obtained. Molecular weight characterization showed the increase of 4HB monomer composition which led to the decrease of molecular weight from 369.3 kDa to 34.0 kDa. CONCLUSION The mixed substrate cultivation was proven to be a promising strategy to increase both polymer production and 4HB monomer composition in single stage production. This serves as a platform for further bioprocess development of copolymer with various 4HB monomer compositions. © 2013 Society of Chemical Industry

Phase Transitions of Polystyrene-b-poly(dimethylsiloxane) in Solvents of Varying Selectivity

A simple method to create a variety of nanostructures via the self-assembly of a single composition silicon-containing block copolymer (BCP) is developed. By using selective solvents for the self-assembly of polystyrene-block-poly(dimethylsiloxane) (PS–PDMS), the phase behavior of intrinsic BCP can be enriched due to the strong segregation of the PS–PDMS enabling the diversity of the phase behavior of PS–PDMS/solvent mixtures and clear-cut phase transitions upon solvent evaporation. The solution-state phase behaviors of the strong segregation BCP system in different solvents are systematically studied using temperature-resolved and time-resolved SAXS experiments. A variety of phases, such as sphere, cylinder, gyroid, lamellar phases and even inverted phases, can be acquired by simply tuning the selectivity of solvent for casting. Meanwhile, owing to the high etching contrast of the silicon-containing block versus the PS block, various nanostructured SiOC can be fabricated by using one-step oxidation. This...

Recent Trends in Nano Metal Polymer Composite

The present paper reviews recent patents on polymer-inorganic particle blends with reference to silver particulate films on softened polymer composites of polystyrene (PS)/ poly (2-vinyl pyridine) (P2VP) and PS/ poly (4- vinylpyridine) (P4VP) deposited at a rate of 0.4 nm/s held at a temperature of 457 K in vacuum of 8x10-6Torr by evaporation. There has been continuous development in the field of polymer-inorganic nano particle blends. Polymer-inorganic particle blends are incorporated into structures involving interfaces with additional materials can be used for forming desirable devices. Polymer blends with a vast variety of characteristics, architectures with properties that are often not accessible with individual components are prepared. A method is used to form metal nanoparticles having a desired shape and size by combining in a single solution, solvent, metal ions and copolymers under conditions such that metal nanoparticles are formed. Nanoparticles layers can be distributed on a substrate using various methods. Blending of insulating polymers with metal particle provides an insulating cover and cost reduction. Various methods are used to design nanoparticle on a dielectric substrate for desired applications like charge storage in electronic devices, system and optical sensors.

Chain Exchange in Binary Copolymer Micelles at Equilibrium: Confirmation of the Independent Chain Hypothesis.

The mechanism of chain exchange in block polymer micelles at equilibrium is investigated using time-resolved small-angle neutron scattering (TR-SANS). The binary micelles are formed from blends of two poly(styrene-b-ethylene-alt-propylene) (PS-PEP) copolymers with different PS core block lengths, only one of which is contrast-matched with the solvent, squalane, so that the monitored scattering intensity only reflects the other species. Micelles prepared with an excess of deuterated PS chains (of the visible species) and those with the equivalent protonated PS chains are blended ("postmixed") at room temperature, where the exchange of chains is suppressed. At several elevated temperatures these samples were monitored by TR-SANS, in which mixing of isotope-labeled visible species gives systematic reduction of scattering signals with time and provides a quantitative way to characterize the micelle exchange kinetics. Within experimental error, the results for each labeled chain (i.e., longer or shorter) in the binary micelles are identical to those recently reported for the same labeled chains in the corresponding single block copolymer component micelles, thus proving that chain exchange in these micelles involves independent chain motion. This reinforces the important conclusions that the single-chain exchange mechanism dominates in the studied micelle solutions and that micelle fusion or fission events are rare.

Effect of Basicity of Amino Group at Side Chain in Diallylamine-Type Copolymer Additive on Via-Filling by Copper Electrodeposition

In a previous study, we achieved the bottom-up via-filling during copper electrodeposition using a single diallylamine-type copolymer additive instead of the conventional four types of additives. However, we have not yet established the relation between the function of this single additive and the polymer structure. To investigate the additive function and the strength of the polymer additive's basicity, we synthesized a series of diallylamine-type copolymers having two amino groups on the polymer side chain, added them to a basic acid copper sulfate bath as a single additive, performed the electrodeposition, and observed the via cross sections using an optical microscope (OM). We also performed an electrochemical analysis based on quartz crystal microbalance (QCM) and linear sweep voltammetry (LSV) measurements. By comparing the amino group at the end of the side chain with the one near the main chain, it was found that the basicity of the latter is weak due to the neighboring group effect. However, when the distance between these two amino groups is long, the basicity of the amino group near the main chain is strong. The use of a polymer additive with a strong amino group near the main chain had the effect of suppressing the electrodeposition outside the via and achieving a good bottom-up filling.