Reaction of nitrogen dioxide with polystyrene films

The reaction of nitrogen dioxide with thin polystyrene films has been investigated at 35°C with different partial pressures of NO₂ (0.1, 2, 15, 30, and 60 cm Hg) and at several temperatures (25, 35, 45 and 55°C). The films were thin enough (ca. 20 μ) so that the reaction was independent of the diffusion of gas into the polymer. The experimental results can be represented by a chain mechanism. The whole degradation process is controlled by the diffusion of polymer radicals out of cages. This diffusion in turn, is affected by the decrease in viscosity or decrease in weight-average molecular weight as degradation proceeds. This leads to an acceleration of the degradation process. A straight-line relationship between the logarithm of the reciprocal weight-average molecular weight and the logarithm of a reaction–time function was found. The dependence on the rate was substantiated by degrading polymer fractions. The energy of activation for the process is small, in agreement with a diffusion process for chain scission. Nitro and nitrite groups are incorporated along the backbone of polystyrene during exposure. The number of these polar side groups appears to pass through a maximum with time, as is evidenced by aggregation of polymer molecules in benzene solution only during the middle stage of the degradation. The final stage of the process is slowed down by retarder being produced. This retarder can be removed by reprecipitation of exposed polymer films. Degradation in solution is similar to that of films. Isotactic polystyrene shows less irregularities in its degradation curve than the atactic polymer. This is, presumably, due to its more homogeneous morphology, large molecular weight, and broader molecular size distribution. The plot of the degree of degradation versus time for the isotactic polymer can be satisfactorily approximated by a straight line.     

Electron spin resonance studies of spin-labelled polymers—I segmental relaxation of polystyrene in solution

From an analysis of the widths of the hyperfine lines in the ESR spectrum of a nitroxidelabelled polystyrene in toluene solution, the correlation times for rotational diffusion at three temperatures have been measured. The values agree well with published data from NMR studies of polystyrene in solution. The value of the activation energy for the relaxation process, 4·3 kcal. mole⁻¹, is close to published values for dielectric relaxation of para-substituted polystyrenes. These comparisons provide strong evidence for associating the ESR correlation times with some form of segmental motion of the polymer backbone.     

Separating the contribution of translational and rotational diffusion to protein association

The association of two proteins is preceded by a mutual diffusional search in solution. The role of translational and rotational diffusion in this process has been studied theoretically for many years. However, systematic experimental verification of theoretical results is still lacking. We report here measurements of association rates of the proteins beta-lactamase (TEM) and beta-lactamase inhibitor protein (BLIP) in solutions of glycerol and poly(ethylene glycol) of increasing viscosity. We also measured translational and rotational diffusion in the same solutions, using fluorescence correlation spectroscopy and fluorescence anisotropy, respectively. It is found that in glycerol both translational and rotational diffusion rates are inversely dependent on viscosity, as predicted by the classical Stokes-Einstein relations, while the association rate depends nonlinearly on viscosity. In contrast, the association rate depends only weakly on the viscosity of the polymer solutions, which results in a similar weak dependence of k(on) on viscosity. The data are modeled using the theory of diffusion-limited association. Deviations from the theory are explained by a short-range solute-induced repulsion between the proteins in glycerol solution and an attractive depletion interaction generated by the polymers. These results open the way to the creation of a unified framework for all nonspecific effects involved in the protein association process, as well as to better theoretical understanding of these effects. Further, they reflect on the complex factors controlling protein association within the crowded environment of cells and suggest that a high concentration of macromolecules does not significantly impede protein association.     

Interactions of a sulfonated ionomer with surfactant in nonaqueous media

The viscometric behavior of dilute solutions of the sodium salt of sulfonated polystyrene (0–6 mol % sulfonation level), with and without surfactant, is investigated to determine the extent of interaction as the structure of the solvent surfactant, and polymer concentration is varied. Reduced viscosity measurements confirm that formation of a polymer–surfactant complex in a relatively polar solvent is controlled to a large extent by charge–charge and hydrophobic forces. The magnitude of these specific interactions is dependent upon the relative polarity of the solvent medium. In a polar solvent, such as dimethylsulfoxide, the hydrophobic forces are strong enough to prevent expansion of the polymer chain at all surfactant concentrations studied. However, in a less polar medium (as in dimethylformamide) the hydrophobic forces are weaker and cannot prevent some chain expansion. It is interesting to note that in this solvent the polystyrene–cationic surfactant complex exhibits a polyelectrolyte effect. Finally, in a lower-polarity medium (cyclohexanone) where the hydrophobic forces are weak, solution behavior is dominated by the interaction of the surfactant with the intramolecular sulfonate ion-pair aggregates.     

Solution behavior of ionomers. I. Metal sulfonate ionomers in mixed solvents

The solution behavior of metal sulfonate-containing ionomers has been investigated in various mixed solvent systems. Ionomers, such as lightly sulfonated polystyrene (sodium salt) and sulfonated ethylene-propylene-diene terpolymer (metal salts) are generally insoluble in typical hydrocarbon solvents, but readily dissolve when small amounts of alcohols or other polar cosolvents are present. At relatively low polymer concentration these ionomers display unusually high thickening behavior in nonpolar solvents when compared with nonionic polymers because of association of the metal sulfonate groups. The addition of modest levels of polar cosolvent markedly decreases the solution viscosity and gives rise to viscosity-temperature relationships different from those of conventional polymer solutions. For example, such solutions can display vicosities which increase, are relatively constant, or display maxima or minima over broad temperature ranges. These observations are interpreted as arising from a temperature-dependent preferential interaction of the cosolvent with the sulfonate groups. While these ionomers can be regarded as polyelectrolytes of low charge density, they do not display the typical “polyelectrolyte” behavior often observed in aqueous solutions. This anomalous behavior is attributed to the fact that the metal sulfonate groups are largely un-ionized in solvents of low dielectric constant. Therefore, the solution behavior is dominated by ion pair interactions rather than free ions.     

Segmental dynamics near the chain end of polystyrene in its ultrathin films: A study by single-molecule fluorescence de-focus microscopy

Rotational motion of fluorophores chemically attached to polystyrene chain-ends in ultra-thin films on solid substrates was studied by single-molecule fluorescence de-focus microscopy. The collective feature of the rotational motion was found and evidenced by the sharp change of the population of fluorophores undergoing rotational motion within a very narrow temperature range (named as the changing temperature, T _c). The T _c value was found to depend on film thickness and interfacial chemistry and the variation of the T _c value is also dependent on the molecular weight of the polymer. The results demonstrate that the spatial confinement effect enhances the segmental mobility near the polymer chain-ends while the interfacial attraction restricts the segmental motion inside the thin film.     

Dielectric effects of step-increased pressure on the mass- and diffusion-controlled linear chain and network macromolecules growth

The dielectric properties of four stoichiometric liquid mixtures of a diepoxide with two monoamines and two diamines have been studied in real time during the mixture's polymerization isothermally to a linear-chain polymer in two cases and a network polymer in the other two cases, at 1 and 200 bar. The pressure was applied: (a) at the beginning of polymerization, (b) after a small extent of polymerization when the viscosity was low, and (c) after a relatively large extent of polymerization when the viscosity was high. For a fixed polymerization period, pressure increased the dielectric relaxation time much more than any other quantity in all cases, without a change in the distribution of relaxation times. Contributions to the dielectric permittivity and loss from physical and chemical effects have been considered and related to the changes in the dielectric relaxation time, viscosity and polymerization-rate constant as the extent of polymerization increased with time. Pressure is expected to decrease the polymerization rate for all conditions, but the decrease is relatively insignificant at the early stage, when polymerization is mass-controlled. Here other effects override the effect of viscosity increase, and the polymerization rate instead increases. The decrease in the rate becomes significant and predominates only when polymerization becomes diffusion-controlled. Since theories of diffusion-controlled reactions do not consider the mutual slowing of the molecular diffusion and the rate of chemical reactions leading to a macromolecule's growth until its vitrification isothermally, a method for determining the onset of diffusion control was needed. It is shown that this onset can be determined from plotting the rate of polymerization against the dielectric relaxation time. Expressed in terms of the dielectric loss, these plots cross each other. The cross-over point indicates the onset of diffusion control. Thus, the effect of pressure on the dielectric behaviour can be used to determine the change from mass-controlled to diffusion-controlled kinetics.     

Dynamics of poly(p‐phenylene) ladder polymers in solution

Photon correlation spectroscopy in both polarized and depolarized geometry was employed to investigate the dynamics of a ribbon‐type polymer exhibiting good solubility. In dilute solution, the translational diffusion for all examined molecular weights has confirmed the picture of wormlike chains with rather short (∼ 7 nm) persistence length (Macromolecules 1997, 30, 273). In the semidilute regime, the total concentration fluctuations display, besides the fast dominant cooperative diffusion, a second slower diffusive process that exhibits weak concentration dependence and is not related to the self‐diffusion measured by pulse‐field‐gradient NMR. The concentration dependence of the cooperative and the self‐diffusion coefficient as well as of the zero‐shear viscosity cannot be consistently described by neither flexible nor stiff chain models. Presence of aggregates was revealed at high concentrations. Owing to the short persistence length, the rotational diffusion is too fast to be adequately investigated. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2211–2220, 1999     

On the interpretation of dielectric relaxation times for uniaxial liquid crystals

The two extensions of the Debye theory of rotational diffusion to include the effect of the orientational ordering potential in uniaxial liquid crystals are compared. The more accurate of these is then employed to analyse the dielectric relaxation times observed for 4-methoxybenzylidene-4′-n-butylaniline. The relationship between the diffusion constant, determined by the analysis, and the twist viscosity coefficient is also discussed.     

Dielectric behavior of some small ketones as ideal polar molecules

The dielectric behaviors of some small symmetric ketone molecules, including acetone, 3-pentanone, cyclopentanone, 4-heptanone, and cyclohexanone, were investigated as a function of temperature (T) over a wide frequency range from 50 MHz (3.14 × 10(8) s(-1), in angular frequency) to 3 THz (1.88 × 10(13) s(-1)). The temperature dependencies of the rotational diffusion times (τ(r)) determined using (17)O NMR spin-lattice relaxation time (T(1)) measurements and viscosities of the ketones were also examined. The obtained temperature dependencies of the parameters for the ketones were compared with those of ideal polar molecules, which obey the Stokes-Einstein-Debye (SED) relationship without the formation of intermolecular dimeric associations and without orientational correlations between dipoles (molecular axes), that is, free rotation. Kirkwood correlation factors (g(K)) of only acetone and 3-pentanone were close to unity over a wide temperature range, whereas those of other ketones were obviously less than unity. These results revealed that no correlations exist between the rotational motions of dipoles in acetone and 3-pentanone, as expected in ideal polar molecules. However, other ketones exhibited orientational correlations in their dipoles because of dipole-dipole interactions via antiparallel configurations. Furthermore, because acetone and 3-pentanone satisfied the SED relationship and because their microscopic dielectric relaxation times (τ(μ)), which were calculated from the determined dielectric relaxation times (τ(D)) via the relationship τ(μ) = τ(D)g(K)(-1), were identical to 3τ(r) and were proportional to Vη(k(B)T)(-1) over the wide temperature range examined, where V, k(B), and η represent the effective molecular volume, Boltzmann's constant, and the viscosity of the liquid molecules, respectively, these two ketone molecules behave as ideal polar molecules. In addition, other ketones not significantly larger than acetone and 3-pentanone in molecular size likely form dimeric intermolecular associations with antiparallel cyclic configurations, which demonstrates the g(K) values less than unity.     

Dielectric relaxation in polar nematic liquid crystals

The relationship between the complex dielectric permittivity tensor of a polar nematic liquid crystal and the autocorrelation matrix for the permanent dipole moment of a molecule is obtained. The theory is applicable to the whole frequency range which characterizes orientational relaxation in liquid crystals (up to ∼ 5 THz). The models of rotational diffusion and extended rotational diffusion in a mean field nematic potential are used to evaluate the dielectric absorption and dispersion in nematics.     

疏水改性聚丙烯酰胺溶液的分子模拟

设计了几种不同的非离子型改性聚丙烯酰胺(HM-PAM)和阴离子型改性聚丙烯酰胺(HM-HPAM). 通过分子动力学模拟(MD)方法研究了在聚合物链上加入不同疏水改性单体对提高聚丙烯酰胺耐盐性的影响, 考察了盐浓度对疏水改性聚丙烯酰胺的回旋半径(R_g)、 特性黏数([η])、 径向分布函数(RDF)和均方位移(MSD)的影响以及聚合物的微观结构与特性黏数之间的关系. 研究结果表明, 引入疏水改性单体后, 改性聚丙烯酰胺具有较好的耐盐性. 通过研究非键作用与氢键相互作用可知, 体系中溶质和溶剂间的相互作用及氢键作用越弱, 溶液的特性黏数越大. O-H原子对的RDF结果表明, 聚合物链的伸展与聚合物链及官能团间的相互作用有关. 当RDF峰较弱时, 聚合物链与水的作用越弱, 越有利于聚合物链保持舒展状态, 溶液的特性黏数也就越大. 另外, 从聚合物链的MSD曲线发现, 聚合链的移动性与特性黏数呈负相关.     

Dependence of viscosity of polystyrene solutions on molecular weight and concentration

Viscosities of solutions of polystyrene in toluene were measured for concentrations up to 400 kg m^?3 at 298 K. Polymers of molecular weights ranging from 8.7 × 10³ to 2.4 × 10⁶ were used. It is observed that viscosity of the polymer solution increases with increasing concentration and molecular weight; the rate of increase is greater at higher values of the two parameters. A master curve for the system is constructed by using the experimental data for viscosity, concentration and molecular weight of the polymer. Regions of various polymer interactions in solution are identified.     

Dielectric studies of photodegradation and photooxidation of polystyrene

The effects of vacuum photolysis at 254 nm and the short-(λ = 254 nm) and long-wave (λ > 300 nm) photooxidations on the dielectric constants (?′) and dielectric losses (?″) of polystyrene have been investigated at 25 ± 1°C. Dielectric constants generally increase on photodegradation, but more pronounced increases occur in the low-frequency region on vacuum photolysis. It is suggested that such increases are associated with Maxwell-Wagner-Sillars polarization. Increases in dielectric losses are observed in three main frequency regions: around 10² Hz, 10⁴ Hz, and at 3 × 10⁶ Hz. The lowest frequency loss which occurs in both the vacuum-irradiated and in the photooxidized samples is attributed to a combination of the effects of interfacial polarization and of the increased direct-current conductivity of the polymer which occurs as a result of these reactions. The 10⁴ Hz dispersion associated only with photooxidation is related to the presence of small, volatile, polar oxidation products, like ketones. The loss peak overlaps the intrinsic γ-relaxation of polystyrene, and it appears that the motions of small molecules, or of relaxing dipoles in these, are coupled to the phenyl group rotational vibrations. The high-frequency losses (3 × 10⁶ Hz) are ascribed to orientation polarization of carbonyl dipoles attached to chain ends, these compounds being produced as a result of hydroperoxide decompositions. A good correlation between the carbonyl dipole relaxation strength and carbonyl concentration is observed. It would appear that relaxation strength measurements could provide quantitative kinetic information for polystyrene oxidation.     

聚苯乙烯链规整度与特性粘数的理论研究

应用构象 构型统计理论和旋转异构态模型 ,考虑大侧基对高分子链构型的影响 ,建立高分子溶液特性粘数与链无规程度的关系 ,并应用于大分子量的聚苯乙烯溶液的特性粘数的计算 ,得到特性粘数与全同、间同和无规链分子量的关系 ,并与实验结果进行比较 ,结果较为满意     

Associating polymers in a well-defined extensional flow field: Influence of solvent quality and polymer concentration

The conformational response of an associating-type random coil macromolecule in solution was investigated utilizing an opposing jet device. This device, capable of generating a well-defined elongational flow field, is quite useful for probing intra- and intermolecular interactions of lightly sulfonated polystyrene ionomers in both nonpolar and polar solvent systems. Below a critical concentration in nonpolar media, such ionomers qualitatively follow trends predicted by dilute solution theory, although intramolecular ionic associations markedly increase the critical elongational shear rate. With further increases in concentration, the extensional behavior is determined by the initial formation of relatively strong intermolecular associations. At even higher polymer concentrations, a third regime is observed where the conformational relaxation process becomes even more facile. On the contrary, in a polar solvent, the conformational relaxation process is markedly enhanced (i.e., critical elongational shear rate is reduced) due to the polyelectrolyte effect, i.e., dissociation of a significant level of the counterions. The effect of this dissociation process influences the relaxation process over the entire concentration region examined. These findings are compared directly with solution rheology, where in low polarity solvents the reduced viscosity is markedly diminished by ion pair-type interactions, and in more polar environments the reduced viscosity is enhanced due to the dissociation of the counterions from the vicinity of the chain backbone.     

The synthesis and modification of low relative molecular weight polybutadiene oligomers

Bulk precipitation polymerization and solution polymerization of butadiene with supported titanium catalyst TiCl₄/MgCl₂-Al(i-Bu)₃ using hydrogen as molecular weight regulator has been performed to synthesize low molecular weight oligomers of trans-1,4-polybutadiene. The effect of the polymerization conditions on the relative molecular weight and structure of the polymer have been studied. Increasing the hydrogen pressure and polymerization temperature resulted in the decrease of intrinsic viscosity of the polymer. By changing the hydrogen pressure, the mole percentage of trans-1,4-unit in the as-obtained polybutadiene can be adjusted, and the maximum value could reach 97%. The degree of crystallinity of the as-synthesized oligomers was about 8–50% with the melting point of form β at about 130–140°C and form α at about 50°C. Through the grafting maleic anhydride, the polar groups were introduced onto the polybutadiene macromolecular chain, which could broaden the application of the non-polar polybutadiene.     

Femtosecond/picosecond time-resolved fluorescence study of hydrophilic polymer fine particles

Femtosecond/picosecond time-resolved fluorescence study of hydrophilic polymer fine particles (polyacrylamide, PAAm) was reported. Ultrafast fluorescence dynamics of polymer/water solution was monitored using a fluorescent probe molecule (C153). In the femtosecond time-resolved fluorescence measurement at 480 nm, slowly decay components having lifetimes of tau(1) approximately 53 ps and tau(2) approximately 5 ns were observed in addition to rapid fluorescence decay. Picosecond time-resolved fluorescence spectra of C153/PAAm/H2O solution were also measured. In the time-resolved fluorescence spectra of C153/PAAm/H2O, a peak shift from 490 to 515 nm was measured, which can be assigned to the solvation dynamics of polymer fine particles. The fluorescence peak shift was related to the solvation response function and two time constants were determined (tau(3) approximately 50 ps and tau(4) approximately 467 ps). Therefore, the tau(1) component observed in the femtosecond time-resolved fluorescence measurement was assigned to the solvation dynamics that was observed only in the presence of polymer fine particles. Rotational diffusion measurements were also carried out on the basis of the picosecond time-resolved fluorescence spectra. In the C153/PAAm/H2O solution, anisotropy decay having two different time constants was also derived (tau(6) approximately 76 ps and tau(7) approximately 676 ps), indicating the presence of two different microscopic molecular environments around the polymer surface. Using the Stokes-Einstein-Debye (SED) equation, microscopic viscosity around the polymer surface was evaluated. For the area that gave a rotational diffusion time of tau(6) approximately 76 ps, the calculated viscosity is approximately 1.1 cP and for tau(7) approximately 676 ps, it is approximately 10 cP. The calculated viscosity values clearly revealed that there are two different molecular environments around the polyacrylamide fine particles.     

Optical, dynamic, and electro-optical properties of poly(N-acryloyl-11-aminoundecanoic acid) in solutions

The optical, electro-optical, and dynamic characteristics of poly(N-acryloyl-11-aminoundecanoic acid) in organic solvents and of the sodium salt of its monomer in water were studied via the methods of flow birefringence, equilibrium and nonequilibrium electric birefringence, and dynamic light scattering. It is shown that, in aqueous solutions, the monomer forms coarse particles of both symmetric and asymmetric shapes. The linear dimensions of these particles are estimated from the data of translational and rotational diffusion. Polymer macromolecules in organic solvents feature negative anisotropy of optical polarizability. Contributions of optical microform and macroform effects to the observed flow birefringence are analyzed in detail. The intrinsic optical anisotropy of the monomer unit of the polymer, which correlates well with the corresponding values for comb-shaped polymers of a similar structure, is estimated. It is shown that polymer molecules lack marked intrinsic permanent macromolecular dipoles and that electric birefringence in their solutions is associated with macroscopic induced dipole moments that appear during orientation of the dipole moments of polar groups in side chains of the polymer under application of an electric field.     

VISCOMETRIC STUDY OF POLY(METHYL METHACRYLATE) AND POLYSTYRENE BLENDS IN DIFFERENT SOLVENTS

The intermolecular interaction between poly(methyl methacrylate) (PMMA) and polystyrene (PS) intetrahydrofuran (THF) and N,N'-dimethyl formamide (DMF) solvents was studied at 28℃ using a dilute solution viscometrymethod. Solvent is believed to play a key role in characterizing the viscosity behavior of the polymer solution. The intrinsicviscosity and viscosity interaction parameter were experimentally measured for the binary (solvent/polymer) and for theternary systems in two solvents. The compatibility of the polymer mixture was discussed in terms of the sign of △b_m. Theresults show that the compatibility of PMMA/PS blend in DMF is larger than that in THF.