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.     

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.     

Properties of extremely high molecular weight polystyrene in solution

Extremely high molecular weight polystyrenes with a $\text{M}\text{?}{}_{\mathrm{w}}$ in the range 10.8 × 10⁶ to 2.2 × 10⁷ were prepared by emulsion polymerization initiated with a heterogeneous initiator at 30°C, which has a ‘living character’. Samples of polystyrene were characterized by light scattering and viscometry in toluene and benzene at 25°C, and in θ-solvent cyclohexane at 34.8°C. Also determined were the relationships of mean-square radius of gyration 〈s²〉 (m²) and the second virial coefficient A₂ (m³ mol kg^?2) on the molecular weight, which for toluene and benzene are described in equations: Toluene (25°C) $\text{〈s}{}^2\text{〉=1.59 × 10}{}^{\mathrm{?23}}\text{M}\text{?}{}_{\mathrm{w}}{}^{1.23}$; $\text{A}{}_2\text{=4.79 × 10}{}^{\mathrm{?3}}\text{M}\text{?}{}_{\mathrm{w}}{}^{\mathrm{?0.63}}$; Benzene (25°C) $\text{〈s}{}^2\text{〉=1.23 × 10}{}^{\mathrm{?22}}\text{M}\text{?}{}_{\mathrm{w}}{}^{1.20}$; $\text{A}{}_2\text{=2.59 × 10}{}^{\mathrm{?3}}\text{M}\text{?}{}_{\mathrm{w}}{}^{\mathrm{?0.59}}$. The parameters in the Mark-Houwink-Sakurada equation were established, for extremely high molecular weight polystyrene in toluene and in benzene, at 25°C into the form giving for $\text{[η] (}\text{m}{}^3\text{kg}{}^{\mathrm{?1}}\text{): [η] = 8.52 × 10}{}^{\mathrm{?5}}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.61}$; $\text{[η] = 1.47 × 10}{}^{\mathrm{?4}}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.56}$. The mentioned relations, as well as the obtained values of Flory parameter ?₀ and of ratio $\text{[η]}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.5}$ were compared with solution properties of high molecular weight polystyrene with narrow molecular weight distribution prepared by anionic polymerization by Fukuda et al.     

Dynamical studies on low molecular weight polyacrylamide aqueous solution

From quasi elastic light scattering and viscosity measurements we deduce the unperturbed dimensions and dynamical power laws of low molecular weight polyacrylamide in 0.1 N NaCl aqueous solutions.     

Functionalization of low molecular weight atactic polypropylenePart II. Thermal and molecular weight studies

Summary Number average molecular weight (M_n), intrinsic viscosity ([η]) and glass transition temperature (T_g) of low molecular weight atactic polypropylene (APP) grafted with 4-allyl-1,2-dimethoxybenzene (DMAB), 4-allyl-2-methoxyphenol (eugenol) and 4-propenylanisole (trans-anethole) in the presence of dicumyl peroxide (DCP) at 170°C were determined. The influences of reaction time, concentration and extent of grafting on M_n, [η] and T_g of APP were examined. The data were discussed with the mechanism of grafting reactions. Received: 6 June 2000/Revised version: 23 July 2000/Accepted: 4 September 2000     

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.     

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.     

Deformation behavior of polystyrene as a function of molecular weight parameters

The mechanical deformation of polystyrene as it relates to molecular weight parameters was investigated. Mechanical testing consisted of uniaxial tension and compression experiments on a variety of polystyrenes. Such quantities as modulus, proportional limit, and various yield stress measurements were determined on polystyrene samples of controlled number-average molecular weight and molecular weight distribution. A basic tool for the mechanical behavior analysis was the use of a power law equation σ = K?ⁿ to examine the initial nonlinear region of each experimentally determined stress–strain curve. Correlations between mechanical deformation and molecular weight parameters were determined using statistical linear regression analysis. It was generally found for uniaxial tension that mechanical parameters in or near the elastic region were independent of M?_n and MWD, while at larger strains correlations were found. For uniaxial compression, stress maxima and the strain where this occurred increased with increasing MWD. Otherwise, mechanical parameter changes in uniaxial compression did not occur with changing M?_n and MWD. Finally, a direct comparison of tension versus compression showed only the initial moduli to be the same. All other mechanical parameters showed significantly differing values, indicating different deformation mechanisms operating in tension verus compression. The analysis of this behavior from both a mechanics and molecular weight viewpoint provides some insight about glassy polymer deformation processes on the microscopic level.     

Hydroxyl group determination in high molecular weight alcohols and complex organic mixtures

Acetylation of complex organic mixtures and high mol wt alcohols is inconsistent by existing procedures because of sample insolubility. By choosing a suitable mixed paraffin-ethyl acetate solvent to bring about nearly instantaneous solu-tion, and utilizing the known catalysis property of perchloric acid, acetylation is quantitative in 10 min or less at room temp. The effect of per-chloric acid concn on these high mol wt systems was studied, and from 0.05-0.45M consistent results were obtained without difficulty. Acetylation of polyethylene oxide (P.E.O.) ad-ducts of straight chain monohydric alcohols pro-ceeds normally and without degradation by the prescribed procedure. Extended reaction time re-sults in partial degradation of the polyether link-ages and amounts to nearly 8% after 30 min.     

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.     

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.     

醇类稀溶液的溶剂萃取研究

介绍了醇类稀溶液的溶剂萃取研究进展。在此基础上 ,提出了醇类稀溶液的萃取分离途径 ,并进行了实验研究。     

The viscosity of concentrated polymer solutions containing low molecular weight solvents

The zero shear rate viscosities of polystyrene/ethylbenzene solutions having polymer weight fractions ranging from 0.5 to 1.0 have been measured using a novel sealed rheometer cell over a temperature range of 50 to 200°C. The concentration and temperature dependence of the solution viscosity has been found to be well described by the relation η₀ = K c^aM_w ^3.4ζ(c, T) where the monomeric friction coefficient ζ is determined by the free volume of the solution. Following the procedure of Berry, the free volume parameters, α_f(c)/γ and T_∞ (c), and the fractional free volume, f(c,T)/γ, have been determined. After using these parameters to account for the concentration dependence of the friction coefficient, the concentration exponent a has been evaluated and found to be in reasonable agreement with the value of 3.4 obtained by Berry and Fox for other polymer/solvent systems. A comparison of the relative conributions made by the friction coefficient and the term c^3.4 to the overall concentration dependence of the viscosity of these highly concentrated solutions shows the friction coefficient to be the dominant factor     

Environmental stress cracking of low molecular weight high density polyethylene

Stress intensity factor (K) — crack speed ($\text{a}\text{?}$) relationships have been obtained for environmental stress cracking (ESC) of specimens of a high density polyethylene having different thermal treatments. Also, scanning electron microscope examination of ESC fracture surfaces has been carried out and correlation between K and the fracture surface appearance has been established. It appears that at low values of K the failure takes place by interlamellar crack propagation; as K increases the mechanism undergoes a transition to void formation and growth, with voids beginning to appear within the spherulites. At high K the failure is entirely by void formation and growth.     

含吡啶小分子胶凝剂研究进展

简述了含吡啶结构的小分子胶凝剂的研究进展,介绍了这类胶凝剂的结构特点、胶凝行为和凝胶性能。