Polystyrenes Of Different Molecular Weights Research Articles

Distance and size dependence of the interactions within highly ordered magnetic nanoparticle mesocrystals

Arranging magnetic nanoparticles (MNPs) into highly ordered structures, so-called superlattices or mesocrystals, is of great interest from a fundamental point of view, as the employment of the corresponding coupled nanoentities introduces additional degrees of freedom to manipulate the overall magnetic characteristics of such hierarchical materials. Characterizing the associated magnetic interactions on the mesoscopic scale is indispensable for obtaining a profound understanding of the relative strengths of the types of interactions involved, such as dipole-dipole interactions, which affect the collective response of a corresponding mesocrystal. In this paper, nanoparticles are deposited onto silicon substrates by spin coating, leading to two-dimensional monolayered structures showing a close-packed hexagonal arrangement. The MNPs consist of iron oxide (magnetite ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$) and are coated with a nonmagnetic polymer (polystyrene). The MNPs are synthesized such that their diameters ${d}_{\text{MNP}}$ are tuned in a range between 9 and 18 nm. A precise manipulation of the shell thickness ${d}_{\text{shell}}$ is achieved by coating the MNPs with polystyrene of different molecular weights. In this fashion, the spacing between the MNPs, ${d}_{\text{spacer}}=2{d}_{\text{shell}}$, is varied in a range between 6 and 14 nm. Within the investigated ${d}_{\text{spacer}}$ range, dipolar interactions govern the collective properties showing distinct distance-dependent characteristics. As ${d}_{\text{spacer}}$ increases, the dipolar coupling strength between the MNPs decreases, as deduced from the spectral features of ferromagnetic resonance experiments. These observations are further corroborated by numerical simulations of the dynamic properties of appropriate model systems. A comparison of the experimental and theoretical findings shows that material parameters, such as the magnetization ${M}_{\text{MNP}}$ and the magnetocrystalline anisotropy ${C}_{\text{MNP}}$ of the MNPs, are reduced compared to their bulk values.

Complexes of end-functionalized polystyrenes carrying amine end-group with transition metals: association effects in organic solvents

Linear end-functionalized polystyrenes of different molecular weights bearing amino end-group (NPS) were synthesized by anionic polymerization high vacuum techniques. The polymers were exposed to copper and iron salts (CuCl2.2H2O and FeCl3.6H2O) to form complexes with specific metal/amino molar ratios. The thermal stability of these complexes was studied by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG), whereas their solution behavior was studied by Low Angle Laser Light Scattering (LALLS), Dynamic Light Scattering (DLS) and dilute solution Viscometry. Extended aggregation phenomena of these complexes were observed in organic solvents. The association behavior was influenced by the molecular weight of the polymer chain, the metal/amine group molar ratio, the chemical nature of the metal and the polarity of the solvent. A complex situation was revealed by DLS showing the existence of equilibrium between aggregates and clusters. Under the influence of shear forces applied in the capillary tube of the viscometer the clusters are disrupted.

One-pot synthesis of bicyclic polystyrene by combination of ATRP and click chemistry

A series of bicyclic polystyrenes of different molecular weights was synthesized in one-pot by atom transfer radical polymerization followed by click chemistry. The bicyclic polystyrenes were formed simultaneously with branched polystyrene impurities due to side reactions during click coupling. The pure bicyclic polystyrenes were obtained by selective precipitation. The purity of bicyclic polystyrenes before purification was determined by Gaussian multiple peak fitting from SEC trace. The bicyclic polymers were characterized by SEC, 1H NMR, and FTIR spectroscopy. Open image in new window

Polystyrene Glasses under Compression: Ductile and Brittle Responses.

Polystyrene of different molecular weights and their binary mixtures are studied in terms of their various mechanical responses to uniaxial compression at different temperatures. PS of Mw = 25 kg/mol is completely brittle until it is above its glass transition temperature Tg. In contrast, upon incorporation of a high molecular weight component, PS mixtures turn from barely ductile a few degrees below its Tg to ductile over 40° below Tg. In the upper limit, a PS of Mw = 319 kg/mol yields and undergoes plastic flow, even at T = -70 °C. The observed dependence of mechanical responses on molecular weight and molecular weight distribution can be adequately rationalized by the idea that yielding and plastic compression are caused by chain networking.

Influence of the molecular weight of a modifier on the phase separation in an epoxy thermoset modified with a thermoplastic

The effect of varying the molecular weight of a thermoplastic modifier on the phase separation in polystyrene (PS)-modified epoxy/amine blends was investigated by comparing blends with PS of different molecular weights. A thermodynamic analysis of polymerization-induced phase separation was performed using a model based on the Flory–Huggins theory, from which the phase diagram and species distribution in the separated phases were calculated. Morphologies developed by the blends were studied in terms of concentration and molecular weight of modifier. Trends in morphologies and thermodynamics of phase separation were exposed and discussed. An increase in the molecular weight of modifier caused a decrease in the miscibility of blend affecting phase diagram, molecular fractionation between the separated phases and morphologies developed showing that molecular weight is a tool to control the final materials.

Hydrophilic methacrylate monoliths as platforms for protein microarray

Hydrophilic macroporous monolithic materials based on a copolymer of 2-hydroxyethyl methacrylate with glycerol dimethacrylate was synthesized by photo-initiated free-radical polymerization of monomers in a presence of the low molecular mass porogens, such as cyclohexanol, dodecanol, toluene and heptane, as well as the solutions of hydrophobic polymers, namely, polystyrene of different molecular weights and concentrations in toluene, and poly(dimethyl siloxane) in heptane. The Hildebrand solubility parameters were used to predict the diluent-polymer compatibility. Pore size distribution and surface area characterization have been assessed by mercury intrusion porosimetry; scanning electron microscopy was used to evaluate the differences in macroporous morphology obtained with different porogenic agents. The monolithic materials were covalently attached to a glass surface directly at polymerization step. Monolithic layers were applied as platforms for microarrays to accomplish highly sensitive solid-phase protein analysis. The efficiency of developed microarrays was demonstrated using mouse IgG and goat anti-mouse IgG as a model affinity pair.

Effects of functional groups on the thermal properties of modified polystyrene

AbstractPolystyrene is, after polyolefins, the most widespread polymer in both industry and everyday life, successfully replacing some raw natural materials. In this study, the chemical modification of polystyrenes of different molecular weights was performed with various functional group modifiers (epichlorohydrin, maleic anhydride, and acetic anhydride) in one stage and in the medium of the cationic catalyst BF3·O(C2H5)2 according to previous studies. The concentration of the functional groups bonded to the aromatic ring of the polymer as a result of the chemical modification of polystyrenes of different molecular weights depended on the molecular weight of the polymer, and more functional groups were bonded to lower molecular weight polystyrene. The effects of the functional groups bonded to the structure of the polymer on the thermal properties of modified polystyrene were investigated. The polystyrene that was modified by maleic anhydride was more stable against thermal destruction at high temperatures. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2549–2553, 2007

Influence of temperature, molecular weight, and molecular weight dispersity on the surface tension of polystyrene, polypropylene, and polyethylene. II. Theoretical

AbstractExperimental data for the surface tension of polystyrenes of different molecular weights (3400–200,000) and different molecular weight dispersities (1–3) and of different polyolefins are compared with the predictions of the Patterson–Rastogi and Dee–Sauer cell theories, which infer the surface tension from pressure–volume–temperature (PVT) data. PVT data for these polymers were obtained from the literature and experimentally and are fitted to the Flory–Orwoll–Vrij equation of state. Both theories predict that the surface tension will decrease linearly with increasing temperature and increase with molecular weight, thereby corroborating the experimental data. However, both theories underestimate the entropy change in the surface formation per unit area at a constant volume for low molecular weight and polydisperse systems and underestimate the effect of molecular weight dispersity on surface tension. Both theories feature two parameters, m and b, that quantify the enthalpic and entropic contributions to surface tension. The theoretical predictions are fitted to the experimental data for monodisperse polystyrene (with a molecular weight above the molecular weight of entanglement), polypropylene, and linear low‐density polyethylene to quantify the enthalpic contribution to surface tension. b is then evaluated as a function of molecular weight and molecular weight dispersity and is found to decrease with increasing molecular weight and to increase with increasing molecular weight dispersity, showing that end‐group excess at the surface has some effect on surface tension. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2201–2212, 2002

Polystyrene Layers Grafted to Epoxy-Modified Silicon Surfaces

Carboxylic acid- and anhydride-terminated polystyrenes of different molecular weights from 4500 to 672 000 were grafted from melt onto silicon substrates modified with epoxysilane monolayer. The grafted chains are densely packed with a density close to the known value for the bulk material. The tethered polymer layers are very smooth, uniform, mechanically stable, and cover homogeneously the modified silicon. At the degree of polymerization (N) close to the critical molecular weight, the grafting process is the most effective, resulting in the grafted unperturbed macromolecules. We suggest that the grafting from the reactive polymer melt is controlled by steric constraints through the minimum available free volume between the grafted macromolecules, which is reachable by another reactive end. This volume correlates with the size of monomeric unit and varies very little with the molecular weight.

Wall slip and absence of interfacial flow instabilities in capillary flow of various polymer melts

We conduct a comprehensive experimental study of melt/wall interfacial slip behavior of various polymer melts in capillary flow. Polymers under study include two polystyrenes of different molecular weights (MW=280 000 and MW=2×106, respectively), two low-density polyethylenes (LDPE), poly(ethylene vinyl acetate) (EVA), and polypropylene (PP). The experimental results reveal an important finding that has greatly extended our previous knowledge of the roles of melt/wall interfacial interactions and molecular entanglements in dictating capillary melt flow behavior. None of the six polymers exhibits an interfacial stick–slip transition or shows any sign of wall slip in bare aluminum dies. Yet, all are found to display a sizable wall slip when the strength of polymer/surface adsorption is reduced by lowering the die wall surface energy with a fluoropolymer coating. The degree of wall slip as characterized by the Navier–de Gennes extrapolation length is demonstrated to be explicitly proportional to the melt viscosity, such that the magnitude of wall slip in the coated die decreases with increasing shear thinning. Diminishing of a measurable wall slip at high stresses explains the well-known absence of spurt, flow oscillation, and sharkskin phenomena in capillary flow of commonly encountered polymers such as PS, LDPE, PP.

Supercritical antisolvent fractionation: measurements in the systems monodisperse and bidisperse polystyrene [sbnd]cyclohexane [sbnd]carbon dioxide

As a model system for new polymer-separation processes utilizing compressed gases the system polystyrenecyclohexanecarbon dioxide with monodisperse polymers (Mw/Mn = 1.09) was investigated experimentally at temperatures up to 250°C and pressures up to 160 bar. Small amounts of carbon dioxide shift the lower critical solution temperature (LCST) to dramatically lower temperatures. When looking at the pressure-concentration representation there is a striking similarity between the effect of temperature and the effect of gas content on the shape of the two-phase region. Pressure has a pronounced effect on the chain partitioning of polystyrenes of different molecular weights in the two liquid phases as determined by gel permeation chromatography. The results are discussed in the context of industrial application.

Isothermal and isobaric PVT-measurements of anionic polystyrenes

PVT-measurements of anionic polystyrenes on heating have shown that, depending on the mode of operation, specific ‘relaxation zones’ within the glass transition range are observed. Isothermal PVT curves exhibit always ‘relaxation zones’ independent whether the pressure is increased or decreased during the scan. The shift of the relaxation zones to higher temperatures is, however, higher for isothermal scans with increasing pressure. These ‘relaxation zones’ are explained by pressure-dependent changes of the state of the polymeric sample isothermally scanned within the glass transition range. At lower pressures the polymer is actually in the molten state, whereas at higher pressures it may be in the metastable glassy state and the actual state depends on the rate of pressure change. In isobaric PVT curves ‘relaxation zones” in heating scans are exhibited only if the pressure applied during glass formation differs from the pressure applied during the heating scan. The observed pressure-dependent shift of the glass temperatures to higher temperatures was higher for the studied polystyrenes of different molecular weight that had a higher glass temperature at normal pressure. But the specific molecular weight influence on the width of the ‘relaxation zone’ could not be ascertained. An attempt to calculate characteristic volume relaxation times failed because of insufficient precision of the measurements.

Miscibility, Microstructure, and Dynamics of Blends Containing Block Copolymer. 3. Molecular Motion in Homopolystyrene and Polystyrene/Four-Arm Styrene-Butadiene Star Block Copolymer Blends

The proton spin-spin relaxation times (T-2(H)) at different temperatures (from 160 to 390 K) have been determined for polystyrene (PS) and four-arm star styrene-butadiene block copolymer (SB-4A) and its blends with PS of different molecular weights (M(PS)

Flow of monodisperse polystyrene solutions through porous media

In this work, we study the origin of the extension thickening commonly observed when solutions of flexible polymers flow through porous media and ideal elongational flows. We have used randomly packed beds of glass beads as porous media. We have performed experiments with closely monodisperse atactic polystyrene of different molecular weights dissolved in organic solvents. The use of a closely monodisperse polymer allowed us to make a more meaningful comparison between the results obtained using opposed jets and porous media flow, as compared to previous works on polydisperse polymers. The results indicate that the coil-stretch transition of isolated polymer molecules in solution cannot be the only mechanism responsible for the extension thickening. It is clear that part of the observed effect is due to the extension of isolated molecules, but the main factor causing a great increase in the elongation viscosity beyond a critical strain rate is the formation of transient entanglement networks.

Study on interdiffusion of polystyrenes of high molecular weight by SANS

The interdiffusion coefficient Dint of polystyrenes of different molecular weights has been measured. The small-angle neutron scattering (SANS) intensity from a sandwich-like sample consisting of alternating deuterated and protonated films is determined as a function of time and analysed with respect to Dint. In the symmetrical case both components have the same molecular weight and interdiffusion coefficients may be scaled according to the reptation theory D ~ M−2. The WLF (Williams–Landel–Ferry) temperature behaviour is observed. In the asymmetrical case using low- and high-molecular-weight polystyrenes, the interdiffusion is dominated by the faster-moving species. The fast-mode diffusion theory best describes the result. The influence of a non-zero Flory-Huggins interaction parameter χ between deuterated and non-deuterated material has been taken into account showing a significant slowing down for the high-molecular-weight material.

Miscibility and kinetics of phase separation in polymer blends of tetramethyl-bisphenol-A polycarbonate and polystyrene

In this paper we report the phase boundaries of tetramethyl-bisphenol-A polycarbonate with polystyrene of different molecular weights, determined using light scattering techniques as well as microscopic methods. The early stages of spinodal decomposition were observed at several temperatures. Analysis of the data using the Cahn-Hillard theory showed that this theory is not able to quantitatively predict the early stages of spinodal decomposition for this blend. Inclusion of thermal fluctuation effects appears to be necessary.

The effect of superplasticizer molecular weight on its adsorption on, and dispersion of, cement

The effect of molecular weight of a superplasticizer on the adsorption on cement was investigated by microelectrophoresis and UV-absorption techniques. The purpose of the experiments was to investigate any differences in the magnitude of the Zeta Potential (ZP) and in the amount of superplasticizer adsorbed by using sulfonated polystyrenes of different molecular weight, MW = 4,000 g/mole, MW = 16,000 g/mole, MW = 31,000 g/mole, and MW = 70,000 g/mole. The results show that the superplasticizer with the largest molecular weight gives the largest negative ZP, and would therefore be assumed to have a higher dispersing capability. UV-absorption results have shown that the polymer of MW = 16,000 g/mole is the most adsorbed of the four superplasticizers, whereas the polymers of MW = 4,000 g/mole, MW = 31,000 g/mole, and MW = 70,000 g/mole are less adsorbed, with MW = 70,000 g/mole being the least adsorbed. That the polymer which is the least adsorbed gives the highest negative ZP is explained by the diffuse double-layer theory.

Radius of gyration and hydrodynamic radius of branched polystyrenes in cyclohexane and toluene measured by static and dynamic light scattering

AbstractThe radius of gyration Rg and the hydrodynamic radius Rh for branched (denoted by subscript b) and linear (1) polystyrenes of different molecular weights were measured both in theta‐ and good solvents. The ratios gg ≡ Rgb/Rgl, gh ≡ Rhb/Rhl, and Rh/Rg were calculated and compared with theoretical predictions based on the Kurata‐Fukatsu theory and its extention to good solvent systems. The following observations were made: gg/ggΘ < gh/ghΘ < 1 and (Rh/Rg)1 < (Rh/Rg)b < 1. The expansion coefficients αg and αh are reduced by the incorporation of branching. Theoretical predictions are qualitatively consistent with these results. The second virial coefficient of branched polymers has a larger molecular‐weight dependence than that of linear polymers, which was explained by a smaller molecular‐weight dependence of Rg. The penetration function of branched polymers is about three times as large as that of linear polymers.

Modifications chimiques du polystyrène: Introduction de fonctions amines primaires en position 3 et 4

Poly(3,4-diaminostyrene) has been prepared by a five-step chemical modification of soluble polystyrene, with a high degree of functionalization; the reactivities of polystyrene aromatic rings and the corresponding benzene compounds have been compared. Polystyrenes of different molecular weight gave similar results; polydiaminostyrenes having particular degrees of polymerization are therefore easily obtained. Modified polymers of high degree of functionalization are slightly cross-linked and swell in aprotic solvents; by limiting the substitution rate in the first step, soluble polydiamines are obtained.

Spatial variation in viscosity in sheared polymer melts

Measurements have been performed using a Weissenberg Rheogoniometer equipped with parallel plates in order to investigate the rheological properties of a polymer melt, namely polystyrene, at very small plate separations. An appreciable gap dependent torque was observed which is indicative of an inhomogeneous viscosity through the sample thickness. The effect is associated with the macromolecular nature of the melt, as confirmed by subsequent measurements performed with polystyrenes of different molecular weight together with a low molecular weight silicone fluid. The results are discussed in relation to models of the molecular chain conformation at a solid-melt interface.