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Poly(1-hexene-co-maleic anhydride) derivatives containing various lengths of linear alkyl side chains (C11–C22) were experimentally evaluated as drag reduction agents in the turbulent flow of Iraqi crude oil using a circulating flow loop system. Good drag reduction performances were obtained. The results showed that the drag reduction has been influenced by the flow rate, concentration, chemical structure, molecular weight, and temperature. Their mechanical stabilities were also investigated using a cylindrical rotator device, and a good relationship was obtained between copolymers' drag reduction efficiency and branch length, in which longer branches significantly enhance copolymer mechanical stability. [ABSTRACT FROM AUTHOR]

Polymeric nanofibers have been the focus of much research due to their continually evolving applications in fields such as biomedicine, tissue engineering, composites, filtration, battery separators, and energy storage. Although several methods of producing nanofibers have shown promise for large scale production, none have yet produced large enough volumes at a low cost to be the front runner in the field, and therefore the preferred choice for industrialization. Rotary jet spinning (RJS) could be the answer to high throughput, low cost, and environmentally friendly nanofiber production. Being exploited in only the last decade, it is a technology that has seen relatively little research, but one which could potentially be the answer to large scale manufacturing of polymer nanofibers. In this review, we focus on fundamental processing characteristics and initial application driven research. A comparison between existing nanofiber production methods is drawn with the key differences noted. Two methods of utilizing RJS in nanofiber production are discussed, namely spinning from a polymer melt, and solution-based spinning as is typically used in more traditional methods such as electrospinning. Modeling of the process is introduced, in which material selection and processing parameters play an important role. [ABSTRACT FROM PUBLISHER]

The molecular basis for rubber elasticity is arguably the oldest and one of the most important questions in the field of polymer physics. The theoretical investigation of rubber elasticity began in earnest almost a century ago with the development of analytic thermodynamic models, based on simple, highly-symmetric configurations of so-called Gaussian chains, i.e. polymer chains that obey Markov statistics. Numerous theories have been proposed over the past 90 years based on the ansatz that the elastic force for individual network chains arises from the entropy change associated with the distribution of end-to-end distances of a free polymer chain. There are serious conceptual objections to this assumption and others, such as the assumption that all network nodes undergo a simple volume-preserving linear motion and that all of the network chains have the same length. Recently, a new paradigm for elasticity in rubber networks has been proposed that is based on mechanisms that originate at the molecular level. Using conventional statistical mechanics analyses, Quantum Chemistry, and Molecular Dynamics simulations, the fundamental entropic and enthalpic chain extension forces for polyisoprene (natural rubber) have been determined, along with estimates for the basic force constants. Concurrently, the complex morphology of natural rubber networks (the joint probability density distributions that relate the chain end-to-end distance to its contour length) has also been captured in a numerical model (EPnet). When molecular chain forces are merged with the network structure in this model, it is possible to study the mechanical response to tensile and compressive strains of a representative volume element of a polymer network. As strain is imposed on a network, pathways of connected taut chains, that completely span the network along strain axis, emerge. Although these chains represent only a few percent of the total, they account for nearly all of the elastic stress at high strain. Here we provide a brief review of previous elasticity theories and their deficiencies, and present a new paradigm with an emphasis on experimental comparisons. [ABSTRACT FROM AUTHOR]

A series of novel transparent shape memory co-polymers, made from (meth)acrylate monomers, intended to be used as intraocular lens, was synthesized. The thermo-mechanical properties, shape memory properties and optical properties of the co-polymers could be adjusted by using monomers with various alkyl chain lengths. The cytocompatibility of the prepared co-polymers to L929 mouse connective tissue fibroblasts was demonstrated in vitro, and the co-polymers exhibited favorable cytocompatibility, supporting cell viability and proliferation. This study showed that the prepared co-polymers, which exhibited good flexibility, adjustable shape memory properties, high transparency and favorable cytocompatibility, could find great promising applications as intraocular lens. [ABSTRACT FROM AUTHOR]

Polyacrylamide (PAM) doped by multiwalled carbon nanotube (MWNT) gels were prepared with different amounts of MWNTs varying in the range between 0.1 and 15 wt%. The PAM–MWNT composite gels were characterized by the steady state fluorescence technique (SSF). The alternative electrical conductivity (AC) of PAM–MWNT composite gels was measured by the dielectric spectroscopy technique. Observations around the gel point, tgel for PAM–MWNTs composite gels showed that the gel fraction exponent β obeyed the percolation result. The critical exponent r of AC electrical conductivity for the composite PAM–MWNT gel was also measured and found to be about 2.0, which agrees with a random resistor network. [ABSTRACT FROM AUTHOR]

Autohesive tack is the ability of two unvulcanized rubber surfaces to resist separation after they are brought into contact for a short period under light pressure. In this work, the effect of unmodified montmorillonite (MMT) nanoclay on autohesive tack of brominated isobutylene-co-p-methylstyrene (BIMS) rubber was investigated by a 180° peel test. The nanocomposites were characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM). The autohesive tack strength dramatically increased with nanoclay concentration up to 8 phr, beyond which it reached apparently a plateau at 16 phr of nanoclay concentration. The tack strength of 16 phr of nanoclay loaded sample was nearly 158% higher than the tack strength of neat BIMS rubber. Various tack governing factors such as green strength, creep compliance, entanglement molecular weight, relaxation time, self-diffusion coefficient, and monomer friction coefficient were analyzed. The addition of nanoclay reduced the extent of molecular diffusion at the tack junction by reducing the chain mobility; however, the diffusion was still sufficient to achieve bond formation. Furthermore, the less diffused chains of the nanocomposite samples showed greater bond breaking resistance due to an increase in cohesive strength, onset of transition zone relaxation time, and monomer friction coefficient value of the BIMS matrix owing to the nanoclay reinforcement. On the other hand, the more diffused chains of the unfilled sample exhibited facile chain separation due to the poor cohesive strength of the BIMS matrix. [ABSTRACT FROM AUTHOR]

The solution properties of polymethylmethacrylate in dimethylsulfoxide were studied using multi-angle light scattering and an online viscometer coupled to size exclusion chromatography. The data demonstrate that DMSO is a suitable eluent for the determination of the molecular weight of PMMA by SEC. The Mark-Houwink coefficients K and α were determined as a function of temperature. At 35°C, DMSO is a theta solvent for PMMA, and it becomes a good solvent as the temperature increases. The unperturbed dimension Kθ was calculated using three different procedures. The data do not show evidence of a conformational transition controlled by the temperature such as the one reported in benzene and confirm the existence of a general relationship between the ratio K/Kθ and α. In the case of PMMA, the comparison of the dipole moment of the side group to that of the solvent can be used to predict the existence of a conformational transition. [ABSTRACT FROM AUTHOR]

Well-defined linear and branched polystyrenes with complex architectures (regular combs and centipedes) were characterized via on-line size exclusion chromatography (SEC), in the good solvent tetrahydrofuran and the theta solvent trans-decalin, in order to measure their radii of gyration ( R g ), hydrodynamic radii ( R H ), and intrinsic viscosities. Various measures of the sizes of these macromolecules were plotted as a function of the retention volume ( V R ) in order to examine the validity of different universal calibration strategies for SEC. Hydrodynamic-based calibration curves were found to be universal, whereas a plot of log R g versus V R did not yield universal curves in either solvent. These findings are consistent with previously published data for linear and branched polymers in thermodynamically good solvents. In addition, good solvent data were used to derive values of the epsilon parameter relating radius of gyration-based and intrinsic viscosity-based chain shrinkage factors. Values of about 0.9 were found for both regular combs and centipedes. [ABSTRACT FROM AUTHOR]

The synthesis of star block co-polymers with polytetrahydrofuran (PTHF) core and poly(tert-butyl acrylate) (PtBA) shell was performed using a dual initiator, 4-hydroxy butyl bromoisobutyrate, by combination of cationic ring-opening polymerization (CROP) and atom transfer radical polymerization (ATRP). The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride provides a triflate ester initiating group for the CROP of THF. PTHF star polymers having three arms with tertiary bromide end groups (PTHF)3 have been prepared by reaction of living PTHF chains with tris(2-aminoethyl)amine (TAEA) in the presence of 2,2,6,6-tetramethylpiperidine (TMP) as a proton trap. Subsequently, the star polymers were used as macroinitiators for the ATRP of tBA using the CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) catalyst system to obtain the tri-armed star block co-polymers (PTHF-b-PtBA)3. The polymers were characterized with gel-permeation chromatography (GPC) and1H-NMR. Both techniques demonstrated the formation of tri-armed star block co-polymers. [ABSTRACT FROM AUTHOR]

The fast transient fluorescence (FTRF) technique was used to study the critical exponents during glass transition in free-radical cross-linking copolymerization (FCC). Methyl methacrylate (MMA), ethyl methacrylate (EMA) and various combinations of MMA with EMA were used during FCC experiments. Pyrene (Py) was used as a fluorescence probe and its fluorescence lifetimes from its decay traces were measured during glass transition. Changes in the viscosity of the pre-gel solutions due to glass formation dramatically increased the Py fluorescent lifetimes, which were used to study the glass transition of MMA, EMA and their mixtures as a function of time, at various temperatures and monomer concentrations. The results were interpreted in the view of percolation theory. The critical exponents, β and γ, were measured near the glass transition point and found to be around 0.37 ± 0.015 and 1.69 ± 0.05, respectively, in all systems studied, which are in good agreement with the static percolation results. [ABSTRACT FROM AUTHOR]

Polymer blending provides a relatively facile means of combining the separate desirable properties of different polymers into a single material. In this paper blends of a low-molecularweight star co-polymer of ε-caprolactone and D,L-lactide with a linear oligo(ε-caprolactone) are prepared and characterized as a possible biodegradable injectable drug-delivery vehicle. The melting characteristics, melt viscosity and degree of crystallinity of the blends were measured, and an in vitro degradation study was performed over a period of 12 weeks. The blends all had a single glass transition temperature and an onset of melting point near body temperature, with the melting point range decreasing as the star co-polymer content increased. The melt viscosity of the blends increased as the star co-polymer content increased, in a manner consistent with miscible blend behavior. The star co-polymer degraded fastest, with a more than 60% mass decrease over the 12-week period. As the oligo(ε-caprolactone) content increased, the degradation rate decreased, with the oligo(ε-caprolactone) exhibiting a mass loss of only 12% over the 12-week period. [ABSTRACT FROM AUTHOR]

This article reviews the subject of characterization of polymer blends with atomic force microscopy (AFM). First., the AFM instrumentation is briefly reviewed, including mechanics, modes of operation, and applicability to the polymer surfaces. Then, AFM studies on polymer blend surface structures and properties are discussed in detail. The surface structures and properties of the polymer blend are affected by bulk concentrations of different components in the blend, the film thickness, the annealing conditions, the substrate, and the solvent for spin coating. AFM has also been applied to monitor the surface structural changes of polymer blends in various environments, such as from air to water, in real time and in situ. In addition, we report examples of semi-quantitative analysis of polymer blend surfaces using AFM force analysis and examples of AFM studies on industrial samples. [ABSTRACT FROM AUTHOR]

The first purpose of this study is to obtain effectively the graft copolymer of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc). Polymerization of VAc in the presence of PVA in dimethyl sulfoxide (DMSO) was investigated. The second purpose of the study is to obtain a PVA having a long branch whose properties have not been clarified yet. By hydrolyzing the PVAc portion in the graft copolymer, the PVA having a long branch might be obtained. The polymerization system was thought to be homogeneous since DMSO is a common solvent for PVA and PVAc at 60°C. Prior to the experiment, solution polymerization of VAc in DMSO was carried out in the absence of PVA to know the chain transfer constant (CS) to DMSO. The CS value was determined to be 0.7×10-4. Then the chain transfer constant to PVA (CP) on the basis of monomer unit was measured to be 9.9×10-4. The CP value was much smaller than the value we had expected, since the CS to isopropanol, whose structure resembles that of the vinyl alcohol unit in PVA, had been reported to be about 5-times larger than this. The reason of the rather smaller value of CP appeared arise from the substantial decrease in concentration of the reactive sites that are buried in the polymer coil. The aimed graft copolymer of PVA and PVAc, as well as the PVA having a long branch, was proved to be rather difficult to obtain, since the reactivity of PVA molecule in the chain-transfer reaction is much lower than that of isopropanol. [ABSTRACT FROM AUTHOR]

In addition to an updated view of the basic principles of viscometry and elastic light scattering molecular-weight-sensitive detectors for size-exclusion chromatography(SEC), this review also examines many of the specific applications described in publications since 2001. These include the use of multidetector systems for validating SEC fractionation, examining polymer conformation, quantifying many forms of polymer topology(e.g., branching), physiochemical studies(e.g., phase separation and aggregation), analyzing oligomers, assessing polymer optical anisotropy, and estimating second virial coefficients. Although multidetector SEC is not without sources of error and uncertainty, it has developed into an extremely powerful analytical method that is increasingly used to accomplish diverse and difficult polymer analyses. [ABSTRACT FROM AUTHOR]

*Reprinted from Star and Hyperbranched Polymers; Mishra, M.K., Kobayashi, S., Eds.; Marcel Dekker, Inc.: New York; 1999, 1–25. [ABSTRACT FROM AUTHOR]

The article presents some Theological results obtained on a large domain of shear rates for semidilute solutions of ultrahigh-molecular-weight poly(methyl methacrylate) at different concentrations. The observed unusual behavior was explained as being due to the flow instabilities of long-chain polymers in an entangled state. [ABSTRACT FROM PUBLISHER]