Molecular Weight Polystyrene Samples Research Articles

High-pressure density and viscosity of polystyrene solutions in methylcyclohexane

High-pressure density and viscosity data of polystyrene solutions in methylcyclohexane have been generated at 340, 360, 380 and 400 K using a falling-cylinder type viscometer up to 35 MPa. Measurements were conducted with two different molecular weight polystyrene samples ( M w=50 000 and 700 000) in the concentration ranges of 3–14 wt.% (for M w=50 000) and 1–5 wt.% (for M w=700 000). Isothermal density and viscosity of these solutions increased linearly with pressure in all the concentration ranges investigated. The flow activation volume and flow activation energy of the polymer solutions were in the range of 29–55 cm 3 mol −1 and 7–10 kJ mol −1, respectively. It was found that the activation volume increased with temperature, and the activation energy decreased with pressure. Viscosity was correlated with density employing a Doolittle type equation η= A exp[ B/(1− V 0 ρ)]. The estimated closed packed volumes ( V 0) from these correlations were in the range of 0.66–0.72 cm 3 g −1 for these solutions.

Small-angle X-ray scattering with imaging plate application to dilute polymer solutions

A new small-angle X-ray scattering apparatus with a pinhole slit collimation camera and an imaging plate detector was constructed and tested with two polystyrene samples of molecular weights 1 × 104 and 2 × 104 in cyclohexane at 34.5°C (the theta point) and toluene at 15°C and also with aqueous aurous colloids. This apparatus requires no desmearing procedure. Its usefulness for polymer solution studies is demonstrated by the measured radii of gyration and scattering functions.

Solid state NMR investigation of antiplasticization of polystyrene by mineral oil

AbstractThe effects of mineral oil plasticization of polystyrene were investigated as a function of polystyrene molecular weight and mineral oil concentration. Solid state NMR, thermo/mechanical methods and positron annihilation spectroscopy (PAS) were used to study the molecular dynamics and free volume effects of this blend. Antiplasticization was observed in the low (40,000) molecular weight polystyrene samples as an embrittlement of the system. In contrast, the flexural modulus was not affected by the presence of mineral oil in the higher (270,000) molecular weight polymers but a decrease in the flexural strength was observed with increasing mineral oil concentration. The NMR and PAS data indicated that the mineral oil was not dissolved in the polymer at ambient temperature, rather it phase separated even at very low concentrations. This caused antiplasticization in low molecular weight polymers because the small free volume holes were filled causing a densification of the system. With high molecular weight polystyrene, this phase separation was manifested as a decrease in the flexural strength.

Depolarized Rayleigh scattering from short-chain polystyrene in a .THETA.-solvent

Depolarized Rayleigh spectra of low molecular weight polystyrene samples in dilute solution in bicyclohexyl, a θ-solvent at 61°C, were obtained. The spectra fit well to single Lorentzian line shapes which were assigned to the overall reorientation motion of the highly anisotropic polymer. The relaxation times at different molecular weights scale with the Stokes-Einstein-Debye equation. The obtained hydrodynamic volumes reduced to a simple monomer unit, show a maximum at w ≃ 2000, apparently reflecting increasing coiling with increasing chain length

Plastic‐rubber composite, 1. The polymer‐polymer interdiffusion at the phase boundary of poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) and polystyrene

AbstractThe interdiffusion of poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) (PPE) and polystyrene (PS) sequences is the key step in the formation of the commonly called plastic‐rubber composite (Kunststoff‐Kautschuk‐Verbund, K&K‐V). This new process bonds PPE and poly(styrene‐co‐butadiene) rubber (SBR) during the vulcanization of the rubber, without the aid of any adhesive. As PPE and PS are fully mutually compatible polymers, polymer‐polymer interdiffusion takes place readily. PS was therefore used as a model system. Electron microscopy clearly demonstrates that the kinetics of the diffusion process are determined by the faster diffusing PS. This was studied in the temperature range of 180°C to 260°C. The interdiffusion coefficients are of the order of 10−13 to 10−10 cm2 · s−1. These are significantly higher than the selfdiffusion coefficients of PPE and PS, which are 10−15 and 10−12 cm2 · s−1, respectively. The interdiffusion coefficients are dependent on temperature and inversely proportional to the PS molecular weight, for PS molecular weights higher than the entanglement value. The diffusion process follows Fick's law. The interdiffusion coefficient is not, or is only weakly, dependent on the concentration. The interdiffusion of PS samples of molecular weights below the entanglement value is observed by a newly developed method based on Fourier transform infrared spectroscopy with attenuated total reflection technique (FTIR‐ATR). In this low‐molecular‐weight region, interdiffusion coefficients as high as 10−7 cm2·s−1 are obtained.

The use of a densitometer as a detector for gel permeation chromatography

AbstractA commercially available densitometer, DMA 60 (Anton Paar, Austria), in combination with a Model DMA 602‐W flow cell was used as a detector in a Waters Model 200 GPC equipped with differential refractive index and ultraviolet absorbance detectors. The density measuring cell was thermostatted to ±0.004°C and the sample injection concentration was 1.5 mg/mL. Polystyrene samples of molecular weights ranging from 9000 to 860,000 were used. The optimum period was found to be 10,000 oscillations, a setting which gave good resolution and a sufficient number of data points to define the chromatogram. The molecular weight averages calculated using the density outputs compared well with those obtained through the conventional UV detector. A sliding average technique was applied to the densitometer data for reducing the baseline noise. It was found that concentrations as low as 1.0 mg/mL (≈0.114%) could be used to obtain densitometer chromatograms that yield molecular weight averages comparable to those obtained from the ultraviolet detector. This densitometer thus appears suitable to be used as an additional GPC detector for routine analyses.

Polystyrene fluorescence spectra. Molecular weight dependence in different solvents

The emission spectra from polystyrene samples of molecular weights ranging from 500 to 612,000 were measured in solvents of different thermodynamic character. The excimer to monomeric emission ratio depends upon the polymer molecular weight but is independent of the solvent. The molecular weight dependence is explained in terms of a distribution of the excimer traps among the macromolecules.

Effect of polymer molecular variables on drag reduction

Abstract Drag reduction is the reduction in energy loss in turbulent flows caused by high polymer or other additives. Although the phenomenon was first observed independently by Mysels and by Toms over three decades ago, the complex interactions of the polymer molecules and the turbulent flow are still not well understood. This paper reviews some of the unusual flow characteristics of drag-reducing solutions, discusses potential applications, and points out the limitations posed by mechanical degradation. The effect of polymer molecular weight, molecular weight distribution, concentration, and solvency on drag reduction are shown for narrow molecular weight polystyrene samples and their mixtures. Various hypotheses for predicting the onset of drag reduction are discussed and compared with measured onset values. The data are best fit by a time-scale hypothesis which depends on the ratio of a molecular relaxation time to a characteristic time of the flow (Deborah number). Two measures of the relative effectiveness of drag-reducing agents are discussed and results for a number of polymers in hydrocarbon solutions are given.

Quasielastic light-scattering measurements of diffusion coefficients in polystyrene solutions

Abstract Measurement of translational diffusion coefficients by laser light scattering has been proposed as a convenient, rapid, and accurate method for characterization of macromolecular species in solution. We have determined diffusion coefficients at infinite dilution in various solutions of a series of narrow molecular weight polystyrene samples and found that the data are consistent with only one of two studies reported in the literature. The concentration dependence of the diffusion coefficient for molecules of different particle weight is investigated, and the infinite dilution values are used to access the unperturbed hydrodynamic dimensions and the excluded volume. The diffusion data are compared with the corresponding intrinsic viscosity values and related to the particle weight. Finally a simple method for evaluating macromolecular polydispersity is described and applied to two polystyrene samples with broad molecular weight distribution.

Molecular weight distributions of standard polystyrene samples by GPC and by sedimentation velocity analysis

AbstractIn precision gel permeation chromatographic (GPC) work, the spreading (zone spreading) characteristics of the instrument must be calibrated. Standard samples of anionic polystyrene have been used for this purpose. The molecular weight distributions of these standard samples, nevertheless, have not been determined carefully. In this work, several standard polystyrene samples obtained from Pressure Chemical Company were examined by GPC and by sedimentation velocity analysis. The results show that (1) the high molecular weight polystyrene samples have skewed molecular weight distributions as has been suspected and that (2) the present data treatment technique for GPC is effective for these very narrow‐distribution samples.

Calibration of instrumental spreading for GPC

AbstractThe proper use of the method for correcting instrumental spreading in GPC requires a precise calibration of the spreading characteristics of the instrument. Heretofore, such a calibration could be obtained only through the tedious reverse‐flow experiments. A more rapid method of calibrating instrumental spreading is presented in this work. This method uses the leading halves of the chromatograms of several standard polystyrene samples. These chromatograms are normally used in the calibration of molecular weight; additional experimental steps are therefore not required. The calculation of the instrumental spreading characteristics from these chromatograms is also relatively simple. The instrumental spreading characteristics were found to depend on the elution volume but not on the nature of the polymer. Thus, calibration results from using polystyrene standards can be used to treat chromatograms for other polymers. For the present GPC instrument, the spreading was found to reach a maximum at an elution volume near 400,000 in polystyrene molecular weight. The existence of this maximum is in agreement with observations made by other investigators and is and indication that diffusion in the mobile phase is not an important contribution to instrumental spreading. The problem of skewing or tailing is discussed. Indication of skewing was observed for one of the higher molecular weight polystyrene samples but the extent of skewing was not severe at the present flow rate of 2 ml/min.

Variation of refractive index of polystyrene with molecular weight: Effect on the determination of molecular weight distributions

AbstractSensitive refractive index measurements on solutions have indicated that the narrow molecular weight polystyrene samples prepared by the Mellon Institute method exhibit a small systematic molecular weight–refractive index dependence up to 300,000 and higher. This upper limit is higher than had previously been suggested. Sensible consistency is generally assumed above a few thousand molecular weight. The effect on this molecular weight–refractive index dependence on gel permeation chromatography and light‐scattering molecular weight measurements on polystyrene standards is illustrated.

Viscoelastic Properties of Polystyrene Solutions

Quartz crystals resonant in the fundamental torsional mode at frequencies of 40 and 73 kc/sec have been used to measure the viscoelastic properties of solutions of polystyrene in toluene, methylethylketone, and cyclohexane. A monodisperse polystyrene sample of molecular weight 2.39×105 was employed. The results have been compared with those of Harrison, Lamb, and Matheson (1964) for dilute solutions in toluene of a number of polystyrene samples of different molecular weight. In toluene, it is found that 25% of the contribution of the polymer to the viscosity of the solution is not able to take part in viscoelastic relaxation, and that the dynamic viscosity at high frequencies (the “Einstein viscosity”) is greater than the solvent viscosity. Under these conditions, the viscoelastic behavior of all time solutions of toluene of polystyrene samples of different molecular weights agrees with the predictions of the Rouse theory. From time value obtained for the Einstein viscosity of the solutions, it is shown that the radius of time equivalent hydrodynamic sphere is approximately proportional to the square root of the molecular weight of the polymer molecule. The viscoelastic behavior of the solution in methylethylketone is intermediate between the predictions of the Zimm and Rouse theories.

The viscoelastic properties of polystyrene solutions

Quartz crystals resonant in the fundamental torsional mode at frequencies of 40 and 73 kc/s have been used to measure the viscoelastic properties of solutions of polystyrene in toluene, methylethyl ketone and cyclohexane. A monodisperse polystyrene sample of molecular weight 2.39 x 10 5 was employed. The results have been compared with those of Harrison, Lamb & Matheson (1964) for dilute solutions in toluene of a number of polystyrene samples of different molecular weights. In toluene it is found that 25 % of the contribution of the polymer to the viscosity of the solution is not able to take part in viscoelastic relaxation, and that the dynamic viscosity at high frequencies (the ‘Einstein viscosity’) is greater than the solvent viscosity. Under these conditions the viscoelastic behaviour of all the solutions in toluene of polystyrene samples of different molecular weights agrees with the predictions of the Rouse theory. From the value obtained for the Einstein viscosity of the solutions, it is shown that the radius of the equivalent hydrodynamic sphere is approximately proportional to the square root of the molecular weight of the polymer molecule. If one assumes that the radius of the equivalent hydrodynamic sphere of a given polymer molecule is the same in all solvents, then the viscoelastic behaviour of the solution in methylethyl ketone is intermediate between the predictions of the Zimm and Rouse theories. The solution in cyclohexane seems to show behaviour close to that predicted by the Zimm theory. The possibility of using such measurements to determine molecular weight distributions is discussed.

A comparison of the thermal gradient and elution methods of polymer fractionation

The elution method is essentially a single-stage process, whereas the thermal gradient method is a multistage process which depends upon a thermal gradient to bring about reprecipitation of polymer in the fractions. As a test of the effectiveness of the thermal gradient, comparisons have been made of fractionation by these two column methods on high molecular weight polystyrene samples. It was found that the thermal gradient method definitely provides superior resolution and reproducibility, as expected. However, the degree of fractionation obtained by the elution method was surprising, accounting for at least 80% of the sample under the usual conditions and giving complete fractionation with certain modifications of conditions. These results indicate the difference in performance of the two methods is less than expected from an elementary consideration of the operation of the columns, and fractionation by the elution method, as conducted here, exceeds that expected for a single-stage extraction process. Although the reasons for the observed behavior are not clear, the following conclusions have been reached about certain factors which influence fractionation. Alternative methods of controlling the concentration of polymer in the fractions give almost equivalent results but enhanced resolution of the high molecular weight portion of the sample is obtained with extended solvent gradients. The inhibitor, tert-butyl catechol, which it was necessary to add to the solvents to limit degradation of the very high molecular weight sample, plays a specific role in the fractionation due to a reaction with the polystyrene which alters the fractionation behavior without affecting the molecular weight. Also, trace amounts of chemical heterogeneity in the polymers, presumably hydroxyl groups, have a marked adverse effect on fractionation by the elution method and probably account for molecular weight reversals observed in some fractionations by the thermal gradient method. It is suggested that adsorption on the surface of the beads is responsiblp for the adverse effect of chemical heterogeneity on the fractionation and that possibly an adsorption which increases with molecular weight contributes to fractionation by the elution and thermal gradient methods.