Ultrahigh Molecular Weight Polystyrene Research Articles

A synthetic route to ultra-high molecular weight polystyrene (>106) with narrow molecular weight distribution by emulsifier-free, emulsion organotellurium-mediated living radical polymerization (emulsion TERP)

We propose a route to synthesizing ultra-high molecular weight (>106) polystyrene (PS) having a narrow molecular weight distribution by controlled/living radical polymerization.

On the nature of enhanced segmental mobility at entangled amorphous polymers interfaces

The long-range segmental mobility at symmetric polymer–polymer interfaces and in the polymer bulk has been compared by employing the adhesion approach and differential scanning calorimetry, respectively, by the example of the nascent and vacuum-dried powders of an entangled random-coiled ultra-high-molecular-weight polystyrene (UHMWPS) with a molecular weight of 106 g/mol. It has been shown that the depression in the surface glass transition temperature of UHMWPS with respect to its bulk glass transition temperature cannot be explained by plasticisation of a near-surface nanometre-thick layer via the surface segregation of the solvent and/or monomer residues. Driving forces of the enhanced long-range segmental mobility in ultrathin polymer layers have been discussed.

Gravure printed flexible small-molecule organic light emitting diodes

Small-molecule based flexible organic light-emitting diodes (SMOLEDs) were fabricated by gravure printing. In order to modify rheological properties of the functional ink, the green emitter was embedded into an ultrahigh molecular weight polystyrene (UHMW-PS) matrix. The viscosity of the ink was characterized as a function of the small molecule:UHMW-PS weight ratio and solvent type. The gravure printed SMOLEDs exhibited a maximum luminance of 850cdm−2, a maximum efficiency of up to 7.7cdA−1, and turn on voltage of ∼3.5V. The gravure printed SM:UHMW-PS device exhibits ∼67% higher luminance efficiency comparing to the spin-coated pristine SM device.

Separation of linear and star‐shaped polystyrenes by phase distribution chromatography

The phase distribution chromatographic technique was optimized and applied for the separation of linear and star-shaped polystyrene (PS). For this purpose non-crosslinked, ultra high molecular weight PS coated on different supporting materials was used. The stability of the coating under chromatographic conditions was tested by thermo gravimetric analysis and microscopic techniques. The modification of different column packing materials was tested. Separation according to branching was indicated for different molecular weights of linear and star-shaped PS. The resolution of the separation was improved by changing the density of the stationary phase and the temperature. The separation results were supported by cloud point measurements and the determination of the critical conditions for linear and star-polymers at the same molecular weight.

Poly(glycerin 1,3-dimethacrylate)-based monolith with a bicontinuous structure tailored as HPLC column by photoinitiatedin situ radical polymerization via viscoelastic phase separation

In this article we described our new approach to the polymer monolith with its morphology tailored for HPLC application to small solutes such as drug candidates. We prepared polymer monoliths based on glycerin 1,3-dimethacrylate, GDMA with a bicontinuous structure by in situ photoinitiated free radical polymerization (UV irradiation at 365 nm). Our photopolymerization was carried out with a monodispese ultra high molecular weight polystyrene solution in chlorobenzene uniquely formulated as a porogen. The poly-GDMA monoliths in bulk, rod and capillary thus prepared showed a bicontinuous network-like structure featured by their fine skeletal thickness nearly in sub μm size. This monolithic structure was considered as a time-evolved morphology frozen by UV-irradiation via viscoelastic phase separation induced by the said porogenic polystyrene solution. According to our μHPLC measurement with acetophenone as a model solute, the UV prepared poly-GDMA capillary demonstrated a much shaper elution profile affording higher column efficiency and permeability as compared with the thermally prepared capillary of the same bore size. Our investigation showed experimentally that poly-GDMA monoliths with a well-defined bicontinuous structure could be prepared reproducibly by photoinitiated radical polymerization via viscoelastic phase separation using the said unique porogen. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4651–4673, 2008

Healing of interfaces of high- and ultra-high-molecular-weight polystyrene below the bulk Tg

Abstarct Amorphous bulk samples of high-molecular-weight (HMW) polystyrene (PS) with a weight-average molecular weight M w of 102.5 kg/mol and a number-average molecular weight M n of 97 kg/mol and of ultra-high-molecular-weight PS (UHMWPS) with M w =1110.5 kg/mol and M n =965.6 kg/mol were brought into contact to themselves below the glass transition temperature T g of the bulk T g-bulk , in a lap-shear joint geometry, at a constant healing temperature T h for a healing time t h of 10 min to 24 h. The lap-shear strength σ of the symmetric HMWPS–HMWPS and UHMWPS–UHMWPS interfaces has been measured at the ambient temperature. Larger values of σ have always been measured for the HMWPS–HMWPS interface after healing at the same conditions. However, the difference between the values of σ for the HMWPS–HMWPS and UHMWPS–UHMWPS interfaces observed at T h = T g-bulk −33 °C and T h = T g-bulk −23 °C became negligible at T h = T g-bulk −13 °C at long times. The kinetics of strength evolution at the two interfaces involved at T h = T g-bulk −33 °C and T h = T g-bulk −23 °C was found to follow the form σ ∝( t h ) 1/4 ( M n ) −1/4 , in accordance with the minor chain reptation model, suggesting that the build-up of the interface structure develops via the diffusion of chain segments above T g of the interface layer T g-interface .

Modeling strain hardening of polydisperse polystyrene melts by molecular stress function theory

The strain hardening of blends of polystyrene (PS) and ultra-high molecular weight polystyrene (UHMW-PS) in elongational flow is modeled by the molecular stress function (MSF) theory. Assuming that the ratios of strain energies stored in polydisperse and monodisperse polymers are identical for linear and nonlinear deformations, the value of the only non-linear parameter of the theory in extensional flows, the maximum molecular stress fmax, can be determined and is shown to be related to steady-state compliance Je0. Using only linear-viscoelastic data, the elongational viscosity of PS/UHMW-PS blends is consistently predicted by the MSF theory.

Relaxation Dynamics of Polymer Liquids in Nonlinear Step Shear

Relaxation dynamics of entangled polymer liquids are investigated in nonlinear step shear flow using mechanical rheometry experiments and theory. Entangled solutions of high molar mass polystyrenes (PS), 3 × 105 ≤ φM̄w ≤ 1.6 × 106 g/mol, in diethyl phthalate (DEP) are the main focus of this study. Cone-and-plate rheometer fixtures roughened by attachment of a single layer of 10−30 μm silica glass beads are used to eliminate interfacial slip during step shear measurements. A simple theory for stress relaxation dynamics that accounts for coupled relaxation of molecular orientation, chain stretching, and entanglement density is used to analyze the experimental results. In PS/DEP solutions with φM̄w ≥ 5 × 105 and in which PS forms an average of eight or more entanglements per chain, we find that the nonlinear relaxation modulus can be factorized into separate strain-dependent and time-dependent functions only after a time λk2 ≈ τd0 ∼ (φM̄w)3 substantially larger than the longest Rouse relaxation time τRouse of the solution. This finding is consistent with results from a previous study of step shear dynamics in solutions of ultrahigh molecular weight polystyrene, M̄w = 2.06 × 107 [Sanchez-Reyes, J.; Archer, L. A. Macromolecules 2002, 35, 5194], but contradicts expectations from current theories for entangled polymer dynamics, which predict λk2 ≈ (3 − 5)τRouse. The origin of this discrepancy is traced to a greater than expected influence of entanglement loss and recovery processes on polymer relaxation dynamics in nonlinear step shear flow.

Step Shear Dynamics of Entangled Polymer Liquids

Nonlinear step shear dynamics of entangled solutions of an ultrahigh molecular weight polystyrene (PS20M, = 20.06 × 106 g/mol) in diethyl phthalate (DEP) are investigated. PS20M/DEP solutions with concentrations φ spanning the range from marginally entangled to highly entangled liquids are used to quantify the effect of entanglement density on dynamics. Step shear measurements are performed in a setting where errors due to interfacial slip can be determined and minimized. Two characteristic “separability” times λk1 = (16.5 ± 4.7)τRouse and λk2 ≫ τRouse are identified, beyond which nonlinear shear relaxation moduli G(γ,t) = σ(γ,t)/γ can be factorized into separate time-dependent G(t) and strain-dependent h(γ) functions. Contrary to expectations from theory, both separability times are stronger functions of polymer concentration (λk1 ∼ φ 0.7, λk2 ∼ φ3.2) than expected for a pure Rouse stretch relaxation route to factorability, λk ∝ τRouse ∼ φ 0. On the other hand, we find that a single shear damping function, h(γ), close to the universal damping function hDE-IA predicted by Doi−Edwards theory accurately describes the strain dependence of step shear material response, irrespective of PS20M/DEP entanglement density.

Kinetics simulation of high viscous styrene bulk polymerization system

Ultra high molecular weight polystyrene could be prepared by rare earth catalyst systems. Monte Carlo method simulates the kinetics of high viscous system of styrene bulk polymerization and verifies our coordination polymerization mechanism presumptions. The simulation indicates β-hydrogen elimination and monomer transfer reaction are important in the whole polymerization while the deactivation reaction and cocatalyst transfer reaction are in small possibilities. Polymers containing double bond end are regarded as macro-monomers that can be initiated into active chain. Monte Carlo simulation proves such presumption and calculates the average branch degree of 0.5.

Synthesis of ultra-high molecular weight polystyrene with rare earth-magnesium alkyl catalyst system: general features of bulk polymerization

Bulk polymerization of styrene (St) with an in-situ-activated Ziegler-catalyst containing neodymium 2-ethylhexyl phosphonate [Nd(P204)3], magnesium–aluminum alkyls and hexamethyl phosphoramide (HMPA) was studied. The new rare-earth catalyst exhibited high activity for polymerization of styrene, and its catalytic efficiency reached 14 730 g PSt/g Nd. The influence of reaction parameters, such as Mg/Nd, Mg/Al, St/Nd molar ratios, temperature, etc, on the catalyst performance was examined in detail. The molecular weight of the resulting polystyrene is ultra-high (MW = 40 × 104 ∼ 120 × 104 g mol−1) and the distribution of molecular weight is broad (MW/Mn = 2.1 ∼ 2.8). The microstructure of the polystyrene was characterized by IR and 13C NMR spectroscopies and found to be atactic. © 2001 Society of Chemical Industry

Structures of a Semidilute Polymer Solution under Oscillatory Shear Flow

The structures of a semidilute polymer solution, comprised of ultrahigh molecular weight polystyrene as a solute and dioctyl phthalate as a solvent, under oscillatory shear flow were investigated b...

Elongational viscosity for miscible and immiscible polymer blends. II. Blends with a small amount of UHMW polymer

The effect of miscibility on elongational viscosity of polymer blends was investigated in homogeneous, miscible, and immiscible states by the blend of 1.5 wt % of ultrahigh-molecular-weight (UHMW) polymer. The matrix polymer was either poly(methyl methacrylate) (PMMA), or poly(acrylonitrile-co-styrene) (AS) that has a comparable elongational viscosity value. The homogeneous blend consisted of 98.5 wt % of PMMA and 1.5 wt % of UHMW–PMMA. The miscible blend was composed of AS and UHMW–PMMA at the same ratio. The immiscible blend was a combination of AS and UHMW–polystyrene (PS) at the same ratio. The strain-hardening behavior of the different blends were compared with that of pure PMMA. It was demonstrated that 1.5 wt % of UHMW induces a strong strain-hardening property in the homogeneous and miscible blends but was hardly changed in the immiscible blend. The optical microscope observation of the immiscible blend suggested that the UHMW domains were stretched, but that the degree of domain deformation was less than a given elongational strain. It was concluded that the strain-hardening property is strongly affected by the miscibility of UHMW chain and matrix. The strong strain-hardening property is caused by the deformation of the UHMW polymer. UHMW chains are stretched when they are entangled with surrounding polymers. However, UHMW chains in an immiscible state are not so deformed because of viscosity difference and no entanglements between domain and matrix. A smaller degree of UHMW chain deformation in immiscible state results in weaker strain-hardening property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 961–969, 1999

Polystyrene degradation induced by stresses resulting from the freezing of its solutions

AbstractSolutions of polystyrene in p‐xylene were frozen in liquid nitrogen. No changes in molecular weight and distribution were caused by freezing solutions for a series of narrow distribution polystyrenes with molecular weights of near 2 × 106 and lower. Likewise a commercial polystyrene of M̄w = 234,000 showed no change, even after 45 cycles of freezing and thawing. However, an ultrahigh molecular weight polystyrene (M̄w = 7.3 × 106) showed appreciable degradation even after a few freezing cycles of its solutions. The changes in molecular weight and distribution were analyzed by gel‐permeation chromatography. The results depended very much on the choice of solvent, cooling rate, and concentration. The extent of degradation was found to depend on polymer concentration in two distinct ways. Indeed, two different degradation mechanisms have been distinguished at low and at high concentrations. The change between mechanisms took place between 1.0 and 2.5 g/l. for polystyrene in p‐xylene. This appears to provide a rare measure of polymer‐polymer interactions (entanglements) in dilute solutions. Degradation in the entanglement region proceeded via a random chain‐scission mechanism as tested by the Scott method. In contrast, at low concentrations degradation was characterized by the formation of appreciable amounts of low molecular weight polystyrene. The presence of an antioxidant (Ionol) during freezing did not change the extent of degradation significantly.