Pressure dependence of the second virial coefficient of dilute polystyrene solutions

The pressure derivatives of the second virial coefficients [dA₂/dP; 0.1 ≤ P (MPa) ≤ 35.0] for dilute polystyrene (PS) solutions in good, θ, and poor solvents were measured with static light scattering. The solvent quality improved (dA₂/dP > 0) in the good and poor solvents that we investigated (toluene, chloroform; and methylcyclohexane) but deteriorated (dA₂/dP < 0) in θ solvents (cyclohexane and 50‐50 cis,trans‐decalin). The effects of temperature [22 < T (°C) < 45] and molecular weight [25 × 10³ < weight‐average molecular weight (amu mol^?1) < 900 × 10³] on dA₂/dP for PS/cyclohexane solutions were examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3070–3076, 2003     

Demixing in polystyrene/methylcyclohexane solutions

Cloudpoint data for polystyrene/methylcyclohexane solutions extending over moderate ranges of pressure and molecular weight are available in the literature. Those data are supplemented with new results from this laboratory to fill in gaps and extend the MW range (to 761 ≤ MW/amu ≤ 2 × 10⁷). The resulting data net is discussed and reasons to extend studies to higher pressure are presented. © 1996 John Wiley & Sons, Inc.     

Chain scission in polystyrene by impact fracture

The number of chain scissions n_s per unit fracture area by impact in high-molecular weight polystyrene is determined to be approximately 3.3 × 10¹⁴/cm² at room temperature. This is almost 20 times larger than would be expected if chain scissions took place only at, or very close to, fracture surfaces. This result was obtained by measuring the molecular weight decrease and the total fracture area of the impact fragments by using size exclusion chromatography and statistical particle size measurements, respectively. The large n_s strongly indicates that significant chain breakage occurs during crazing before the propagation of cracks. An average craze thickness before breakdown under impact is estimated from n_s to be around 2 μm. In a diluted polymer, n_s is found to be significantly lower than the extrapolated value, assuming a linear dilution of entangled chain crossings at the fracture surface. This low chain scission density, however, can be explained by taking into account the reduction of craze breakdown strain in the diluted polymers. Finally, the broken chain ends of polystyrene appear to be stable under ambient conditions. © 1992 John Wiley & Sons, Inc.     

Flow‐Induced Polymer Degradation During Ink‐Jet Printing

We report for the first time evidence of flow‐induced polymer degradation during inkjet printing for both poly(methyl methacrylate) (PMMA) and polystyrene (PS) in good solvent. This has significance for the deposition of functional and biological materials. Polymers having either less than 100 kDa or greater than approximately 1 000 kDa show no evidence of molecular weight degradation. The lower boundary condition is a consequence of low Deborah Number De imposed by the printhead geometry and the upper boundary condition due to visco‐elastic damping. For intermediate molecular weights the effect is greatest at high elongational strain rate and low solution concentration with higher polydispersity polymers being most sensitive to molecular weight degradation. For low polydispersity samples, PDi ≤ 1.3, chain breakage is essentially centro‐symmetric induced either by turbulance or overstretching when the strain rate increases well beyond a critical value, that is the stretching rate is high enough to exceed the rate of relaxation. For higher polydispersity samples chain breakage is consistent with almost random scission along the chain, inferring that the forces required to break the chain are additionally transmitted either by valence bonds, i.e. network chains and junctions or discrete entanglements rather than solely by hydrodynamic interaction.

     

Rheological measurements and light-scattering experiments of dilute solutions of high molecular polystyrene. Light-scattering of flowing polymer solutions

We describe the behavior of dilute polymer solutions by means of light-scattering under shear flow. Solution properties of polystyrene in benzene over a wide range of molecular weight has been studied to determine the coefficientsa andK of the Mark-Houwink relationship and to estimate the rheological conditions with regard to light-scattering experiments of flowing polymer solutions. The investigations were carried out to measure the shear-rate dependence of macromolecules in solution, e.g., to observe an orientation and changing of the mean-square radius of gyration.     

Energy-consuming micromechanisms in the fracture of glassy polymers. I. Chain scission in polystyrene

The number of chain scissions per unit area that occur during the fracture of partially annealed latex films from M_n ? 180,000 g/mol polystyrene particles of about 275 Å radius were measured and correlated to annealing times. A curve with four regimes was found. At short annealing times the curve is nearly flat, in what is called the chain pull-out regime. In the second regime, the number of chains broken per unit area increases with a 0.8 power of annealing time as entanglement of the diffusing polymer chains increases in neighboring host particles. This is in good agreement with Wool's theory which predicts a 0.75 power dependence. Then, after reaching a peak, the number of scissions decreases in the third regime, indicating a change in fracture mechanism. The number of chain scissions increases again in the fourth regime, as final healing of the film interface takes place. Fracture surface analysis reveals a rough surface for short annealing times and a smooth surface for longer annealing times. The number of polymer chain scissions per unit area of fracture surface showed no dependence on initial molecular weights for t ? τ_r where t and τ_r are annealing and relaxation times, respectively. The number of chain bridges crossing a unit area of interface was suggested as the basic molecular property. © 1992 John Wiley & Sons, Inc.     

Inclusion of the effects of polydispersity and volatility on the random chain scission statistical analysis for polymer degradation

The statistical product distribution for a linear polydisperse polymer of finite molecular weight was included into the statistical analysis for a system undergoing random chain scission showing the effect of volatilization of species other than monomer. Two sets of equations were derived. One set is for the nonvolatile fraction; the other is for the volatile fraction. Within each set there are three equations, one for the number of polymer molecules, the second for the molar (or number) fraction, and the third for the weight fraction of polymer molecules containing a specific number of repeat units. As degradation proceeds the polydispersity index should converge to a value of 1 rather than 2, which has been reported previously. The expected effects of polydispersity, number‐average degree of polymerization, and volatility were treated individually, and we determined that the molecular weight of a polymer has no theoretical influence on the product distribution. As for the effect of volatility, we determined that only the volatile product distribution would change. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3690–3696, 2000     

Miscibility and phase behavior in atactic polystyrene and poly(o-chlorostyrene-co-p-chlorostyrene) blends: Effect of polystyrene molecular weight and copolymer composition

Miscibility in blends of random copolymers of o-chlorostyrene and p-chlorostyrene [P(oClSy-co-pClS_1-y)] with 8 atactic polystyrene (aPS) fractions has been studied at temperatures ranging from 150°C to 300°C. Miscibility windows whose size depends on the molecular weight of the PS and on the copolymer composition, y, were observed for each blend. From these data, the temperature dependence of the three segmental interaction parameters required to describe this system were obtained.     

Sulfonation of polystyrene: Toward the “ideal” polyelectrolyte

Sulfonation of narrow polydispersity polystyrene, PS, standards remains the method of choice for generating polystyrene sulfonate, PSS, samples with defined composition. Although a variety of sulfonation techniques have been described, relatively little is reported on the material obtained, which is used for so many studies on the fundamental behavior of polyelectrolytes. Here, we show that powdered polystyrene treated with concentrated sulfuric acid (96%) at 90 °C without catalyst yields fully sulfonated PSS. Extensive characterization with ¹H and ¹³C NMR as well as size exclusion chromatography coupled with static and dynamic light scattering shows no evidence of sulfone crosslinking or chain degradation under the conditions used. Though mono‐sulfonated as soon as it dissolves in the acid, the PSS contains about 6% meta substitution. Sulfonation kinetics for this heterogeneous reaction depend strongly on particle size, sulfuric acid content and temperature. For preparing perdeuterated PSS from the corresponding PS it is essential to employ D₂SO₄, as about half of the aromatic units undergo H/D exchange during sulfonation. The remaining ortho H/D may be exchanged with extended exposure to the concentrated sulfuric acid, but the meta site is deactivated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2416–2624     

Change and Convergence of Polymer Distribution During Nonrandom Degradation

The CLD development during nonrandom degradation is investigated, assuming the rate of bond scission depends on the chain length and the position of the bond within the chain. As the degradation proceeds, the polydispersity index usually approaches a fixed value pertinent to the degradation mechanism, independent of the initial distribution. The exact limiting values are presented for several cases. These values may be useful to estimate the degradation mechanisms. For example, if the limiting PDI is smaller than 2, the bonds in larger chains may be easier to break than shorter ones, and if it is smaller than 4/3, the size effect is not enough and the breakage may tend to occur in the middle of the chain.

     

Temperature dependence of the conformational relaxation time of polymer molecules in elongational flow: Invariance of the molecular weight exponent

Using an elongational flow technique, we have investigated the relationship between the molecular conformational relaxation time and the molecular weight for a solvent whose quality was altered thermally from near θ to a good solvent state. The materials used were closely monodisperse samples of atactic polystyrene. The results show that the relaxation time τ varies with the molecular weight M as τ ∝ M^1.5, independent of the solvent quality, a result which apparently is at variance with the observed molecular weight dependence of intrinsic viscosity. Despite this invariance of the molecular weight exponent with solvent quality, our results also show that the coils do expand when the solvent quality was increased in agreement with the mean-field theory of Flory.     

Nonlinear viscoelastic diffusion in concentrated polystyrene/ethylbenzene solutions

Nonlinear gradient-driven diffusion was studied in concentrated polystyrene (PS)/ethylbenzene (EB) solutions using vapor sorptions with a finite driving force. The nonlinear sorptions were carried out on thin films (≅2.05, 3.50 μ thick) at conditions where non-Fickian, “viscoelastic” effects appear. These data were modeled with the nonlinear diffusion equation studied by Tang. Four dimensionless material parameters in the model were determined from a limited amount of linear-response, differential sorption data on PS/EB mixtures measured in the same range of experimental conditions as for the nonlinear sorptions. The nonlinear model successfully predicts the observed nonlinear response either above or below the glass transition (T_g). In order to simultaneously capture the nonlinear response both above and below T_g, the abrupt change in the concentration dependence of physical properties at T_g must be accounted for. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2103–2119, 1997     

Associated inter‐ and intrachain conformational transitions in polystyrene solutions

Understanding the conformational changes of polymeric chains in solutions is an essential and integral part of polymer physics. By increasing the concentration of polymer solutions from dilute to semidilute regime, the critical chain overlapping has been reported at the concentration termed as C*. In this study, the associated inter‐ and intrachain conformational transitions in polystyrene (PS) solutions are reported. By comparing the spectroscopic intensity ratio versus concentration for an intrachain PS system, a break point was observed in good solvent which coincided with the theoretically predicted C*. Moreover, the intrachain conformation showed no obvious change below C*, while significant collapse started to occur above C*. This result reveals a new insight in polymer physics, since traditionally the size of polymer chains is considered to decrease weakly regarding the concentration change in the semidilute regime. It is important to find such an abrupt intrachain conformational transition between the dilute and semidilute solutions and provide the first experimental observation that inter‐ and intrachain conformational transitions are correlated to one the other. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1373–1379     

Phase separation in dilute polymer solutions at high‐rate extension

In this article the demixing instability and phase segregation in unentangled polymer solutions of semiflexible chains at high‐rate uniaxial extension above the coil to stretched coil transition was studied. Orientation of the stretched chains was described in terms of an effective potential field. Based on the free energy analysis it was shown that the flow‐induced orientation of polymer segments could drastically reduce the energy of their steric repulsion. As a result attraction between the chains gain more importance, and this effect lead to the demixing process and eventual segregation of polymer from the solvent if the strain rate exceeds some critical value. A mean‐field theory was developed to study this flow‐induced phase separation effect. The phase diagrams of the system showing the spinodal and binodal transitions at different extension rates were calculated and discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1066–1073     

聚对苯乙烯磺酸钠添加剂的分子量对水煤浆浆体性质的影响

选用了变质程度不同的八种煤和三种不同分子量的聚对苯乙烯磺酸钠（PSS）添加剂,详细考查了该添加剂的分子量对水煤浆浆体性质的影响。结果发现,在考查PSS相对分子量的范围内（质均分子量为5.34×104～33.39×104）,八种煤的水煤浆成浆性随着分子量的增大而增加,水煤浆成浆性与PSS添加剂的平均分子量的关系可归因于添加剂在煤粒上的吸附,分子量小的PSS在煤粒上的吸附量大于分子量大的PSS;PSS分子量的增加有利于水煤浆的流变性由胀性向假塑性转变;PSS分子量的增加使水煤浆的静态稳定性得到显著的改善。     

Relative molecular weight distributions of cis-polybenzoxazole/polyphosphoric acid rodlike liquid crystalline polymer solutions from dilute solution rheometry

The molecular weight for a dilute solution of cis-polybenzoxazole (PBO) in polyphosphoric acid (PPA) was determined by fitting the rheological data with a semiempirical polydisperse hybrid theory. The hybrid theory models a semiflexible rigid rod as an elastic cylinder. The cylinder has both a rotational relaxation spectrum given by an ideal rigid rod and an internal bending relaxation spectrum spaced in accord with the relaxation time spectra of a flexible coil with fully developed hydrodynamic interactions. The model was fitted to rheological data collected for a 0.05 weight percent solution with intrinsic velocity (one-point determination) of 320 ± 10 cc/g. The model predicts a number-average molecular weight near 12800 ± 400 g/mol with a polydispersity index of 2.5 ± 0.1. By using the Yamakawa-Yoshizaki equation the intrinsic viscosity is calculated for the model molecular weight distribution as 310 cc/g.     

Stress overshoot of polymer solutions at high rates of shear; Polystyrene with bimodal molecular weight distribution

Overshoot of shear stress, σ, and the first normal stress difference, N₁, in shear flow was investigated for dilute solutions of polystyrene with very high molecular weight in concentrated solution of low M PS. In the case that the matrix was a nonentangled system, behavior of overshoot was similar to that of dilute solution of high M PS in pure solvent. The magnitudes of shear, γ_σm and γ_Nm, corresponding to the peaks of σ and N₁ lay on the universal functions of γ˙τ_R, respectively, proposed for dilute solutions in pure solvent. Here τ_R is the Rouse relaxation time for high M PS in the blend evaluated from dynamic modulus at high frequencies. In the case that the matrix was an entangled system, an additional σ peak was observed at high rates of shear at times corresponding to γ_σm = 2–3. This peak can be assigned to the motion of low M chains in entanglement network. When the matrix was entangled, stress overshoot was observed even at relatively low rates of shear, say γ˙τ_R < 10⁻². This is probably due to the motion of high M chains in entanglement of all the chains. In this case the γ_σm and γ_Nm values were higher than those expected for entangled chains of monodisperse polymer in pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2043–2050, 2000