Solvent dependence of the viscous and viscoelastic properties of a high molecular weight polystyrene in moderately concentrated solution

The steady-flow viscosity and viscoelastic behaviour of two solutions of a sensibly monodisperse polystyrene of high molecular weight (M_w = 498 000) have been measured over a temperature range of 100°C for identical concentrations of 20.55 wt.%. Toluene and methyl ethyl ketone were chosen as the two low viscosity solvents having, respectively, good and marginal thermodynamic affinities. Dynamic viscoelastic measurements were made at a frequency of 41 kHz using travelling torsional waves. At this frequency, both solutions exhibit behaviour characteristic of the rubbery region, and the ratio of the dynamic viscosity normalised by dividing by the corresponding solvent viscosity is independent of the solvent until the onset of the glass transition region with decreasing temperature. The storage shear modulus of the toluene solution in the rubbery region is higher than for the MEK solution, indicating a higher entanglement density in the better solvent and a larger polymer radius. Some features of the results in the poor solvent (MEK) appear to indicate that, as the temperature decreases, partial exclusion of the solvent leads to the formation both of stronger entanglements and of macromolecular aggregates or bundles, as suggested by Dreval and others^6–8,11,22.     

Toughness of two pure block copolymer blends in high molecular weight polystyrene

Blends of two commercial pure block copolymers, Phillips KRO-1 and KRO-3 Resins, in high molecular weight PS were prepared by solvent casting techniques to produce composite spherical particles with two different morphologies in a majority phase of the high molecular weight PS. One type of particle had the typical KRO-1 Resin morphology of randomly wavy and often interconnected PB rods in a topologically continuous block copolymer phase of PS, while the other type of particle made of KRO-3 Resin was in the form of concentric shells of alternating layers of PB and PS block copolymer phases. Both blends were found to result in only a marginal improvement of the toughness of homo PS even for particle volume fractions as high as 0.22. This inadequate performance in the case of the KRO-1 Resin blends results from the relatively large stiffness of the KRO-1 particles, while in the case of the KRO-3 Resin blend, it results from too small an average particle size, even though the particle stiffness in the latter case is low.     

Mechanical degradation of high molecular weight polymers in dilute solution

The mechanical shear degradation of polydisperse polyisobutene and monodisperse polystrene in oils of different viscosities in the concentration range of 0.1% to 1% was studied using a high-shear concentric cylinder viscometer under laminar and uniform well-defined shear field conditions. Molecular weight distributions (MWDs) were measured by gel permeation chromatography (GPC). Degradation of polydisperse polyisobutene solutions narrows the distributions principally through the breaking down of large molecules. Degradation of monodisperse polystyrene broadens the distributions at lower shear stress. At higher shear stresses, the distributions do not broaden as much but are still broader than those of the original polymer. The final M_w/M_n ratios are considerably different from the value of 2 expected for random degradation. Hence, the degradation is likely a nonrandom process. It was found that the extent of degradation has a negative concentration dependence coefficient at relatively high molecular weight and a positive concentration dependence at lower molecular weight. Competing mechanisms of “stretching” and “entanglements” for degradation were postulated to explain the results. The degradation data indicate that the shear stress is the controlling parameter, not the shear rate. The shear degradation is independent of initial molecular weight and viscosity of the solvent.     

Preparation of high molecular weight monodisperse polystyrene latexes by concentrated emulsion polymerization

The preparation of high molecular weight monodisperse polystyrene (PS) latexes by the concentrated emulsion polymerization is investigated. The PS latexes thus obtained have diameters in the range of 0.1–0.3 μm. The average size and the dispersity of the latexes are dependent on the concentration of surfactant (SDS), the monomer volume fraction, and the amount of monpolymerizable additive (decane). The ionic strength does not seem to affect the size but affect the dispersity of the latexes. Under proper conditions, monodisperse particles can be prepared with a quite small standard deviation. © 1993 John Wiley & Sons, Inc.     

Light scattering characterisation of polymers II. Analyses of high molecular weight polystyrene

For light scattering analysis of an extremely high molecular weight polymer with large size in solution, use of mixtures of a given polymer with its low molecular weight homologue is described to have great advantages. With such bimodal mixtures as test samples, one can alter the unknown form of the angular variations of scattered lights to a form to be expected and widen the range of the linearity with sin² (ø/2), where ø is the scattering angle. According to the considerations, a sample of linear polystyrene was successfully analysed on a commercial apparatus, Fica 50 to have the weight-average molecular weight of 27 million.     

Stirring-induced solution crystallization of ultra high molecular weight polyamide 6

Unstable solutions of ultrahigh molecular weight polyamide 6 have been prepared by adding a nonsolvent to the polymer solution. Crystallization of the polyamide from such a solution proceeds very slowly. It has been found, however, that vigorous stirring of the unstable solutions induces rapid fibrous crystallization of the polymer. The fiber mat consists of irregularly shaped fibers. A low temperature and a high stirring rate are among the conditions necessary to obtain a high yield of fibrous material. The fibers formed upon stirring have a higher molecular weight than the polyamide 6 molecules which remain in the solution. The melting point of the fibers depends on the speed of the paddle stirrer. The differential scanning calorimetry (DSC) thermogram reveals higher melting temperatures of the fibrous material if higher stirring rates have been applied.     

Electrochemically controlled molecular weight of polystyrene production

Summary It is well known that physical properties such as mechanical and thermal characteristics of a polymer are highly dependent on its molecular weight and molecular weight distribution (MWD). This feature encourages our interest for finding suitable conditions that allow us to control the molecular weight of the formed polymer, by controlling the experimental parameters. We are reporting some results about the electropolymerization of styrene in tetrahydrofuran with tetrabutylammonium tetrafluoroborate and sodium tetraphenylboron as supporting electrolytes. From the electrolyses using tetrabutylammonium tetrafluoroborate two molecular weight distribution curves, showing weight average molecular weight values ( ) of 3.6×10⁵–1.7×10⁶ for the first and 5×10³ for the second one were observed. When using sodium tetraphenylboron a unique distribution curve was displayed suggesting that the weight average molecular weight of the polystyrene, increases by increasing the current density; the observed MWD being rather low.     

Chain conformation and viscometric behaviour of high molecular weight polystyrene in solvent/nonsolvent mixtures

Summary Viscometric studies on high molecular weight polystyrene in solvent/nonsolvent binary mixtures are reported. Polymer behaviour is affected by the preferential adsorption phenomena determining the appearance of two theta temperatures, one intramolecular (B=0, -1) and the other intermolecular (A₂=0). For very high molecular weight polystyrene, theta intramolecular strongly approaches theta intermolecular due to a decrease in selective adsorption and in the vicinity of the theta condition the conformation transitions disappear.     

Properties of polyurethane oligomeric blends versus high molecular weight block copolymers

Segmental compatibility has been investigated in both oligomeric polyurethane blends and polyurethane block copolymers. The block copolymers are formed by linking a hard segment, composed of three MDI and two butane diol units on average with various macroglycols. The monodisperse oligomeric hard segment, H₃, with its chain ends reacted with ethanol is used as the urethane component in blends with macroglycols. The macroglycols used in both the blend and block copolymer systems include polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), and polybutadiene (PBD). Blends of H₃ and PEO form a eutectic at a weight ratio of $\text{≈20}\text{80}\text{(}\text{H}{}_3\text{/}\text{PEO}\text{)}$ with a T_m,e = 34°C. H₃ and PTMO blends also give rise to a eutectic composition at $\text{≈20}\text{80}\text{(}\text{H}{}_3\text{/}\text{PTMO}\text{)}$ but with a T_m,e = 10°C. Both PPO and PBD mix with H₃ to form a crystalline—amorphous blend. The miscibility of H₃ and the soft segments at the melting point of H₃ is in the order of PEO > PTMO > PPO > PBD. In the block copolymer systems, stress—strain and dynamic mechanical testing indicate that the block copolymerization of a hard segment with each soft segment results in a microphase separated elastomer as expected. The extent of phase separation increases in the order of PBD > PTMO > PPO > PEO which is coincident with the trend predicated by the application of Hilderbrand's solubility parameter concept. All the soft segments used occur in an amorphous phase in the block copolymers while PEO and PTMO crystallize in a blend with H₃. The differences between the properties of the blends and block copolymers suggest that the phase separation, segment crystallization and domain coalescence are substantially restricted by the urethane—polyol junction points.     

Rheological behavior of low molecular weight polystyrene composites containing monodisperse crosslinked polystyrene beads

Steady shear viscosities and dynamic moduli of polymer composites, consisting of crosslinked polystyrene beads and low molecular weight polystyrene matrix, were measured in a cone-and-plate rheometer at different temperatures. Viscosities and dynamic moduli were found to be very sensitive to filler loading and measurement temperature. Steady shear viscosities of 30% and 40% loaded low molecular polystyrene composites showed a power-law behavior over the entire range of shear rates. Storage and loss moduli were initially linear with frequency on double logarithmic plots, with limiting slopes of 0.3 and 0.1. At high concentration of filler particles, they showed a flat plateau at low frequencies, indicating that these systems exhibit a yield behavior. A 20% PS composite loaded with beads of high crosslink densities resulted in poor dispersion of beads as a result of poor dispersion of particles. PS beads 1.16 μm in diameter showed a higher viscosity. It is due to the apparent increase in loading resulting from broken particles. At low measurement temperature, filler effects were suppressed by high viscosity matrix and showed a similar rheological behavior to high molecular weight by PS matrix. We suggest that rheological behavior reflects the state of dispersion of beads in the matrix.     

Temperature gradient interaction chromatography of low molecular weight polystyrene

Separation of low molecular weight polystyrene (PS) by temperature gradient interaction chromatography (TGIC) is reported. As in the separation of high molecular weight PS, temperature is an efficient variable to control the retention of low molecular weight PS in the reversed phase HPLC separation. However, a right choice of the eluent, typically a marginal solvent for the polymeric solute of interest, is crucial for the temperature to play an effective role in the retention control. For an example, PS oligomers were well separated by TGIC under the isocratic elution condition of C18 bonded silica and methanol as the stationary and the mobile phase, respectively.     

A convenient route to high molecular weight highly isotactic polystyrene using Ziegler-Natta catalysts and ultrasound

Ziegler-Natta (TiCl₄/AlEt₃) catalysts and ultrasound were used to prepare highly isotactic polystyrene (ca. 99%) with a molecular weight of 4.7×10⁶ mol g⁻¹ and low molecular weight distribution (M_w/M_n=1.6) via a convenient method. Ultrasound was most effective if applied only during an initial stage in the polymerisation, most likely permitting dispersion of catalyst particles which were subsequently coated and separated by growing polymer chains. Yields could be improved by varying the amount of catalyst and reaction time.     

Spinning of high molecular weight polyethylene solution and subsequent drawing in a temperature gradient

Summary The spinning and drawing of high molecular weight polyethylene solution forming ultra-high strength fibres has been studied and occurrances on the molecular level are discussed. The fibre properties were found to be strongly influenced by the drawing stress and the temperature conditions.     

Properties of ultra high molecular weight polyethylene fibers after ion beam treatment

Ultrahigh molecular weight fibers were treated by low energy ion beam in a pulse regime. Results of infrared and WAXD analyses showed the change of both chemical structure and morphology of the fiber surface. Adhesion of the treated fiber surface to conventional binders appeared to be two times higher than that of untreated fiber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Low molecular weight block copolymers as plasticizers for polystyrene

Polystyrene‐b‐alkyl, polystyrene‐b‐polybutadiene‐b‐polystyrene, and polystyrene‐b‐poly(propylene glycol)monotridecyl ether were synthesized using macro initiators and atom transfer radical polymerization or by esterifications of homopolymers. The aim was a maximum molecular weight of 4 kg/mol and minimum polystyrene content of 50 w/w %, which by us is predicted as the limits for solubility of polystyrene‐b‐alkyl in polystyrene. DSC showed polystyrene was plasticized, as seen by a reduction in glass transition temperature, by block copolymers consisting of a polystyrene block with molecular weight of approximately 1 kg/mol and an alkyl block with a molecular weight of approximately of 0.3 kg/mol. The efficiency of the block copolymers as plasticizers increases with decreasing molecular weight and polystyrene content. In addition, polystyrene‐b‐alkyl is found to be an efficient plasticizer also for polystyrene‐b‐polyisoprene‐b‐polystyrene (SIS) block copolymers. The end use properties of SIS plasticized with polystyrene‐b‐alkyl, measured as tensile strength, is higher than for SIS plasticized with dioctyl adipate. The polystyrene‐b‐polybutadiene‐b‐polystyrene and polystyrene‐b‐poly(propylene glycol)monotridecyl ether series were only partially soluble in polystyrene and insoluble in the polystyrene phase of SIS. For the lowest molecular weight samples, this leads to measurable plasticization of polystyrene but no plasticization of SIS. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 981–991, 2005