A study on the concentration dependence of excimer formation in pyrenyl labelled polystyrene solutions

The fluorescence of pyrenyl labelled polystyrene has been investigated. The ratio of excimer to monomer intensities (I_e/I_m) is found to vary tortuously with increasing concentration (C) and displays two critical concentration points, C⁺ at about 3.2 × 10⁻² g ml⁻¹ and C_m at about 0.32 g ml⁻¹. In the region C⁺ < C < C_m, an abrupt increase of I_e/I_m is revealed because of intermolecular interaction. At C > C_m, the sharp decrease of I_e/I_m is ascribed to entanglements of polymer chains. © 1999 Society of Chemical Industry     

Interdiffusion in blends of polystyrene and polymethylstyrene studied by light scattering after temperature jumps across the phase boundary

We describe a simple light scattering set-up for measuring interdiffusion coefficients D in polymer blends by generating spinodal decomposition and subsequent dissolution after temperature jumps across the phase boundary. In blends of polystyrene and polymethylstyrene (random copolymer of 60% m-methylstyrene and 40% p-methylstyrene) D values were obtained between 10⁻¹¹ and 10⁻¹⁵ cm²s⁻¹ at temperatures up to 50 K above the upper critical solution temperature. The results are discussed in relation to tracer diffusion in the same system.     

Polymer-cosolvent systems: 6. Phase behaviour of polystyrene in binary mixed solvents of acetone with n-alkanes-examples of ‘classic cosolvency’

The demixing behaviour of polystyrene fractions in binary combinations of acetone (1) and a series of n-alkanes (2) containing up to twenty carbon atoms has been established and the data presented as phase contour diagrams. Each binary liquid system exhibits the characteristics of classic cosolvency and the maximum molecular weight of polymer that may be dissolved is ca. 10⁶ gmol^?1 in combinations of acetone and tridecane. The shapes of the phase contour diagrams can be related to the solvent behaviour of the n-alkane used towards polystyrene, although cosolvent action is not a simple linear function of the mixture composition.     

Viscosity of polystyrene solutions expanded with carbon dioxide

The viscosity of solutions of polystyrene (PS) in decahydronaphthalene (DHN) was measured in the presence of carbon dioxide (CO₂) with a moving‐piston viscometer. The effects of the CO₂ pressure (0–21 MPa), polymer concentration (1–15 wt %), temperature (306–423 K), and polymer molecular weight (126 and 412 kDa) on the viscosity were investigated. In the absence of CO₂, the increase in the viscosity with increasing polymer concentration was approximately exponential in concentration and was well described by the Martin equation. All the data fell on a single line when the relative viscosity was plotted against cM^0.50 (where c is the concentration of the polymer in solution and M is the molecular weight of the polymer). The viscosity of the polymer solution decreased with increasing CO₂ pressure under otherwise constant conditions. For a given CO₂ pressure, the viscosity reduction was greatest when the relative viscosity was high in the absence of CO₂, that is, for high‐molecular‐weight polymer, high polymer concentrations, and low temperatures. Reductions in the relative viscosity of almost 2 orders of magnitude were observed in some cases. The viscosity of solutions of PS in DHN also was measured in the presence of sulfur hexafluoride (SF₆). At a given pressure, SF₆ was about as effective as CO₂ in reducing the solution viscosity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 540–549, 2006     

Physicochemical characterization of carrageenans—A critical reinvestigation

Kappa‐, iota‐, and lambda‐carrageenan (food grade) were analyzed by static light scattering (MALS in batch mode) in 0.1M NaNO₃ at 25 and 60°C, earlier heated up to 90°C or not. At 25°C, there was a strong tendency for a concentration‐dependent aggregation in the order lambda < kappa < iota. At 60°C, all samples were molecularly dispersed. The strongly temperature‐dependent refractive index increments (equilibrium dialysis) differ. Data interpretation in terms of the wormlike chain model using the Skolnik‐Odijk‐Fixman approach led to an intrinsic persistence length around 3 to 4 nm and expansion factors as high as 1.5 and above in a thermodynamically good solvent for all three types. Triple‐detector HPSEC (DRI, MALS, viscometry) on the three commercial samples plus a degraded (by acidic hydrolysis) kappa‐carrageenan in the same solvent/eluant at 60°C yielded a uniform and slightly curved [η]‐M relationship for 5 × 10³ ≤ M/(g mol) ≤ 3 × 10⁶ and a nearly identical molar mass dependence of the radius of gyration. HPSEC at 25°C on kappa‐carrageenan confirmed formation of soluble aggregates. Special emphasis was put on analytical and methodological aspects. The reliability of the experimental data was demonstrated by analogous measurements on dextran calibration standards. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Grafting of styrene onto polyethylene in near critical media

In this work, near critical n‐heptane is used as reaction medium for the copolymerization of polyethylene with styrene monomer, using alkylation reaction with different amounts of aluminum chloride (AlCl₃) as catalyst. In this way, polyethylene chains will be more available to react with the catalyst. The reaction effect on pure reactants, as well as, the catalyst activity was previously investigated. The reaction occurrence was corroborated by analyzing the reaction products before and after careful polystyrene extraction with tetrahydrofuran. The reaction products were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, and size exclusion chromatography. The possible architecture for the copolymer molecule was proposed from the molecular characterization results. On the other hand, the polystyrene grafting modifies final properties of polyethylene, increasing the oxygen barrier properties without deteriorating significantly the mechanical properties of the films. In this sense this reaction seems to be a promising route to modify PE films to increase the barrier properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dynamic light scattering and viscoelasticity of semidilute polystyrene/cyclohexane solutions

In the present work, dynamic light scattering (DLS) measurements from polystyrene in cyclohexane semidilute solutions were carried out at 60 °C with scattering angles varied from 30° to 120°. The correlation functions were analyzed with the double KWW function and the CONTIN program. The amplitude of the fast mode A_f of the field correlation function g¹(t) was used to calculate the longitudinal stress modulus M_o using Wang’s theory. A comparison between M_o calculated from DLS data and the shear stress modulus G obtained from mechanical measurement was made.     

Molding of syndiotactic polystyrene under its melting temperature

Syndiotactic polystyrene (SPS), a thermoplastic polymer that exhibits a high T_m in some crystalline forms, can be conveniently processed by a cold‐compaction technique. Processing temperatures in the range of 150–210°C, well below the T_m, gives rise to physicomechanical properties comparable and even better than those obtained by thermal compression or injection molding. The optimum treatment temperature seems to fall around 175°C. X‐ray diffraction analysis, thermal analysis, and density measurements suggest that such behavior is connected to phase transitions of SPS and favored by the presence of styrene included in the crystalline fraction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 377–383, 2001     

Phase diagrams of blends of poly(phenylene ether), polystyrene,and diglycidyl ether of bisphenol A: Influence of the molar mass of poly(phenylene ether)

Phase diagrams of ternary blends of poly(phenylene ether) (PPE, M_n = 1.2 and 12 kg mol^?1), polystyrene (PS, M_n = 22.5 kg mol^?1), and diglycidyl ether of bisphenol A (DGEBA) were experimentally obtained in an extended range of temperatures and fitted with the Flory–Huggins model using three binary interaction parameters. A significant increase in miscibility together with the appearance of an immiscibility loop was found for PPEs with M_n values comprised in the range between 1 and 10 kg mol^?1. This enables us to obtain initial homogeneous solutions in regions of high DGEBA concentrations, a possibility that was not previously reported for this ternary blend. This opens new possibilities for the toughening of epoxies replacing a single thermoplastic with a thermoplastic blend where both components (PS and PPE) are completely miscible. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1742–1747, 2006     

Polymerization of methyl methacrylate in the presence of a nonpolar hydrocarbon solvent. I. Construction of a complete ternary phase diagram through an in situ polymerization

This article presents the ternary phase diagram for methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and n‐hexane system at 70°C. It was constructed by both theoretical calculations and online laser light scattering (LLS) technique. In situ polymerization of MMA in a nonpolar nonsolvent carried out in a LLS cell provides a new means for the accurate detection of the cloud points of highly viscous polymer mixtures, with polymer weight fractions over 0.6. The ternary phase diagram measured in this study can be used to design the reaction conditions for the precipitation and/or dispersion polymerization in a nonpolar nonsolvent medium where polymerization kinetics as well as polymer particle morphologies are strongly affected by thermodynamic phase separation phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solution properties of polyaniline

Solution properties of polyaniline (PANI) synthesized at various temperatures were studied using static light scattering (SLS), intrinsic viscosity, and dynamic light scattering (DLS). We demonstrated that average radius of gyration 〈R_g〉, intrinsic viscosity [η], and average hydrodynamic radius 〈R_H〉, of polyaniline molecules in dilute N‐methyl‐2‐pyrrolidinone (NMP) solutions increased with decreasing synthesis temperatures, i.e.; increasing molecular weight. SLS data demonstrate that second virial coefficient (A₂) decreased with increasing particle sizes suggesting that solubility of PANI in NMP decreased with increasing particle sizes. We also find that the polymers extend as the polymer concentration is lowered and that the increase in the hydrodynamic radius can be expressed by a power law of the electrostatic screening length. This behavior is typical of polyelectrolytes in dilute solution, providing a basis for understanding the conformation changes of this metallic polymer in solution. Copyright © 2009 Society of Chemical Industry     

微米级聚苯乙烯/聚硅氧烷核壳微球的制备、表征及其作为光散射剂的应用

在乙醇/水混合溶剂中采用分散聚合法制备出微米级聚苯乙烯微球,将聚苯乙烯核微球与甲基三甲氧基硅烷的水解溶液混合,加入氨水使硅烷水解产物在核表面缩合交联,制备出微米级聚苯乙烯/聚硅氧烷核壳微球.采用TEM、粒径分布仪、EDX、TG等对核壳微球的形貌、粒径、表面成分和热失重进行了表征.将核壳微球作为光散射剂添加在聚甲基丙烯酸甲酯（PMMA）树脂中,制备出性能良好的光散射材料.当SS6核壳微球的添加浓度为1%（质量）时,制得的PMMA样片（2 mm）的雾度为88.16％,透光率为72.5％;当SS6添加浓度为2%（质量）时,其雾度为92.13％.     

Effects of functional groups on the thermal properties of modified polystyrene

Polystyrene is, after polyolefins, the most widespread polymer in both industry and everyday life, successfully replacing some raw natural materials. In this study, the chemical modification of polystyrenes of different molecular weights was performed with various functional group modifiers (epichlorohydrin, maleic anhydride, and acetic anhydride) in one stage and in the medium of the cationic catalyst BF₃·O(C₂H₅)₂ according to previous studies. The concentration of the functional groups bonded to the aromatic ring of the polymer as a result of the chemical modification of polystyrenes of different molecular weights depended on the molecular weight of the polymer, and more functional groups were bonded to lower molecular weight polystyrene. The effects of the functional groups bonded to the structure of the polymer on the thermal properties of modified polystyrene were investigated. The polystyrene that was modified by maleic anhydride was more stable against thermal destruction at high temperatures. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2549–2553, 2007     

Influence of solvent contents on the rubber‐phase particle size distribution of high‐impact polystyrene

High‐impact polystyrene (HIPS) was prepared by the bulk or low‐solvent polymerization of styrene in the presence of dissolved rubber and characterized to measure the dispersed particle size of the rubber phase. Before preparation, the prepolymerization time was established by measuring the evolution of particle size distribution of the dispersed phase as a function of reaction time. The measurement technique by laser light scattering was found to be efficient enough not only to lead to the right prepolymerization time but also to predict rubber‐phase particle size distribution. Polymerization experiments were then conducted to investigate the effect of solvent contents on the particle size distribution of the rubber phase, in which ethylbenzene was introduced as a solvent at levels of 0, 3, 10, and 15%. As the solvent content increased, the size of rubber‐phase particles initially increased, reaching a maximum, and then decreased. It is speculated that a decrease in the molecular weight of the matrix, a decrease in the viscosity ratio between polybutadiene to polystyrene phases, and a change in rubber morphology all contributed to the change in the rubber particle size of HIPS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3672–3679, 2003     

Synthesis of polystyrene nanocapsules by redox interface‐initiated inversed microemulsion polymerization for drug release

Polystyrene nanocapsules with a diameter of 140 nm and a water‐soluble sodium salicylate core were prepared by redox interface‐initiated emulsion polymerization (RIEP) in an inversed microemulsion with cumene hydroperoxide/iron(II) sulfate as the redox initiation couple. The morphology of the nanocapsules was characterized by transmission electron microscopy and field emission scanning electron microscopy. Dynamic light scattering was used to determine the nanocapsule size and polydispersity (0.14–0.20). The release of sodium salicylate from the nanocapsules was monitored by ultraviolet–visible spectroscopy. All of the results indicate that the fabrication of core–shell nanocapsules with the water‐soluble active chemical as the core via RIEP was successful. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymer-cosolvent systems: 5. Upper and lower critical solution temperatures of polystyrene in n-alkanes

The demixing behaviour of low molecular weight polystyrene in three n-alkanes (hexane, heptane and octane) has been established. Critical solution behaviour is a function of alkane chain length, and application of free volume theory shows this to be an entropic effect. The quality of n-alkanes, up to twenty carbons in length, as solvents for polystyrene has been estimated.     

Interfacial tension of demixed polymer solutions near the critical temperature: polystyrene + methylcyclohexane

Interfacial tension between demixed solutions of polystyrene + methylcyclohexane has been measured near the critical temperature as a function of temperature using polystyrenes with molecular weights 9000 ～ 1.26 × 10⁶. The critical exponent for the interfacial tension was determined to be about 1.30 for the lower molecular weight systems. However, for higher molecular weights the exponent could not be obtained because the system departed from critical behaviour. Magnitudes of the interfacial tension were proportional to about N^?0.44, where N is the polymerization index. Experimental results were compared with the recently-proposed theories and found to be in qualitative agreement. The tricritical theory of polymer solutions was also compared with the experimental results.     

Phase‐separation phenomena in the polymerization of styrene in the presence of polyethylene wax

The demixing processes that occur during the polymerization of styrene in the presence of a low molar mass polyethylene wax were investigated. Quantitative information on the phase behavior of such a three‐component system was obtained through the investigation of the temperature‐induced phase separation and the observation of the phase separation during polymerization. Both techniques allow the construction of the same ternary phase diagram. Such phase behavior can be understood through the discussion of the interference of a liquid–liquid phase‐separation process and crystallization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2234–2243, 2004     

Study of viscosity abnormality of PS/toluene solution in extremely dilute concentration regime

The concentration dependence of the reduced viscosity η_sp/c and the translational diffusion coefficient D as well as the radius of gyration R_g of polystyrene in toluene were studied by viscometry and laser light scattering (LLS), respectively. The influence of the experimental error on the determination of the η_sp/c was investigated and a quantitative relation was given out. Viscometric experiment found that the η_sp/c–c curve is clearly divided into two parts by dynamic contact concentration c_s. When c > c_s, it shows normal linearity as predicted by Huggins equation. But when c < c_s, i.e., in the extremely dilute regime, the η_sp/c–c curve is no longer linear and levels off considering the experimental uncertainty. This new finding was confirmed by the following LLS experiment, which indicates that the size of the polymer chains no longer varies with concentration when c < c_s. As a result, we, for the first time, using the method of combination of viscometry and LLS, prove an important conclusion that in the extremely dilute concentration regime, the reduced viscosity of polymer solution, at least for PS/toluene, conforming to the Einstein viscosity equation is just the intrinsic viscosity and independent of the concentration. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4440–4446, 2006     

Molecular weight dependency of refractive index increment of polystyrene determined by uniform oligomers

Molecular weight dependency of a specific UV absorption coefficient of polystyrene in solution was determined by supercritical fluid chromatography applied to equimolar and equimass mixtures of uniform polystyrenes whose degree of polymerization was n = 1 to 40. From the ratio between the response from a UV detector and that from a refractometer, we determined the refractive index increment dn/dc as a function of molecular weight for polystyrene in tetrahydrofuran at the wavelength λ = 633 nm. We found that dn/dc is well expressed as a linear function of the reciprocal of molecular weight for uniform polystyrenes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1101–1106, 2004