Showing papers on "Polystyrene published in 1989"

Two-dimensional infrared spectroscopy

Abstract: Two-dimensional infrared (2D IR) spectroscopy, a novel technique based on time-resolved IR spectroscopy, is introduced In 2D IR, a system is excited by an external perturbation, which induces a dynamic fluctuation of the IR spectrum A correlation analysis is applied to the time-dependent IR signals to yield a spectrum defined by two independent wavenumbers By spreading IR peaks over the second dimension, a complex spectrum consisting of overlapped peaks can be substantially simplified, and spectral resolution is enhanced Peaks located on a 2D spectral plane provide information on connectivity and interactions among functional groups associated with the IR bands 2D IR spectra are presented for a system consisting of a mixture of atactic polystyrene (PS) and low-density polyethylene (PE) to illustrate these features The spectroscopic evidence clearly shows PS and PE in a blend are segregated at the molecular level, allowing the components to respond to an applied external perturbation independently of each other

Influence of coupling agents and treatments on the mechanical properties of cellulose fiber–polystyrene composites

Abstract: Wood fibers of aspen in the form of chemithermomechanical pulp (CTMP) and Tembec 6816 have been used as reinforcing fillers in different varieties of polystyrene. The tensile strength, elongation, and energy at maximum point, as well as tensile modulus at 0.1% strain is reported. Also revealed is the optimum condition of compression molding. The influence of different coupling agents, such as poly[methylene(polyphenyl isocyanate)], silanes (A-172, A-174, A-1100), and grating on the mechanical properties of composites is discussed. The extent of increase in mechanical properties depends on the weight percentage of fibers, the concentration of coupling agents, and the grafting level (add-on %). Coating followed by an isocyanate treatment appears to be the best treatment. In addition, the isocyanate treatment and grafting are superior to the silane treatment. Experimental results are explained on the basis of possible interactions among cellulose fiber-coupling agent-polymer in the interfacial area.

Molecular design of multicomponent polymer systems. XIV. Control of the mechanical properties of polyethylene–polystyrene blends by block copolymers

Abstract: Amelioration notable de la resistance a la traction et de l'allongement a la rupture d'alliages de polystyrene et de polyethylenes differents par addition de 2 a 10% de copolymeres de styrene et de butadiene hydrogene. Etude de l'amelioration en fonction de la structure des copolymeres: copolymeres bisequences plus efficaces. Importance du processus de melange a l'etat fondu et interet de l'addition d'emulsifiants polymeres

Protein adsorption on pluronic copolymer-coated polystyrene particles

Abstract: The effect of surface modification of polystyrene latex particles on subsequent protein adsorption was investigated by photon correlation spectroscopy, sedimentation, and fluorescence anisotropy decay techniques. The surface modifiers used are a series of Pluronic triblock copolymer surfactants (PEO)a(PPO)b(PEO)a (where PEO is polyethylene oxide and PPO is polypropylene oxide). The hydrodynamic thickness of the adsorbed Pluronic copolymers is proportional to the PEO chain length a as well as the molecular weight of the surfactant, with Pluronic F108 and Tetronic 908 having the thickest layers. Undetectable protein adsorption was observed on such surfactant-coated particles. This was demonstrated by monitoring the unchanged particle size upon addition of human albumin, fibrinogen, or whole plasma, in contrast with size increase for the uncoated particles. This result was also confirmed by direct adsorption isotherm measurement using sedimentation method. Furthermore, the unchanged rotational correlation time of the protein molecules upon addition of Pluronic F108-coated polystyrene particles is also consistent with the above finding of protein resistance of the coated particles. Rotational correlation time was determined from the fluorescence anisotropy decay of an extrinsic probe, 1-pyrenesulfonyl chloride, covalently attached to the protein molecules.

Characterization of thermal diffusion in polymer solutions by thermal field‐flow fractionation: Dependence on polymer and solvent parameters

Abstract: The thermal diffusion coefficient DT has been obtained for 17 polymer-solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field-flow fractionation. The polymers examined include polystyrene, poly(alpha-methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent.

Preparation of micron-size monodisperse polymer microspheres having chloromethyl group

Abstract: Micron-size monodisperse polymer microspheres having chloromethyl groups thereon were prepared by two-step polymerization process as follows. First, micron-size monodisperse polystyrene particles were prepared by dispersion polymerization with 2,2′-azobisisobutyronitrile as initiator in ethanol-water medium in the presence of poly(acrylic acid) as stabilizer under various conditions. Secondly, in the presence of the 1.9-Μm monodisperse polystyrene particles produced under the optimum conditions, seeded copolymerization for styrene and chloromethyl styrene was carried out. The seeded copolymerization proceeded smoothly without producing new particles, and it was confirmed by x-ray photoelectron spectroscopy that the chloromethyl group existed more at the surface of the produced microsphere than at that of film cast from the benzene solution in which the microspheres were dissolved.

Preparation of highly sulfonated polystyrene model colloids

Abstract: Previous attempts to prepare monodisperse styrene/sodium styrene sulfonate copolymer latexes by batch, seeded, and semicontinuous emulsion polymerization were unsuccessful at high concentrations of the functional comonomer. Broad, and sometimes bimodal, size distributions, and large amounts of water soluble homopolymer were obtained. After removal of free monomer, solute and adsorbed homopolymer and copolymer, the overall incorporation of the functional comonomer was found to be low. To overcome these problems, a two stage “shot-growth” or in situ seeding technique was developed. A first stage copolymerization was carried out with a low concentration of sodium styrene sulfonate: the purpose of the functional comonomer was to enhance the stability and regulate the size of the seed particles. When this reaction had reached high conversion (> 90%), a second stage monomer mixture was added. The ratio of styrene to sodium styrene sulfonate in this mixture determined the final surface charge density. The mechanism by which the NaSS is incorporated in the polymer particles is considered to be by solution copolymerization with solute styrene monomer to form surface active oligoradicals. These radicals adsorb on the particle surface, initiate polymerization and become inextricably bound, preventing their transfer back to the aqueous phase. By this means, it was possible to vary independently the particle size and surface charge density. High concentrations of functional comonomer could be polymerized without undue wastage (incorporations were only slightly less than 100%) or loss of monodispersity. In extreme cases, the area per functional group fell below the theoretical minimum, indicating considerable hydration of the surface layers.

The effect of unidirectional shear on the structure of triblock copolymers. I. Polystyrene-polybutadiene-polystyrene

Abstract: Rheological and SAXS measurements indicate that high-strain, high-stress unidirectional shear flow in the microphase-separated regime produces a well-oriented, microdomain structure with cylindrical microdomains. Experiments in low-stress, high-strain flow produced little orientation. Flow above the microphase-separation temperature resulted in no microdomain orientation. A flow mechanism for microphase-separated block copolymers proposed previously is compatible with the results obtained here

Morphological studies of micelle formation in block copolymer/homopolymer blends

Abstract: The micellar structure of poly(styrene‐butadiene) diblock copolymer/polystyrene homopolymer blends has been investigated by small angle x‐ray scattering (SAXS) and transmission electron microscopy (TEM) as a function of copolymer concentration, copolymer block molecular weights, and homopolymer molecular weight. The SAXS from blends exhibiting spherical micelles, as evidenced by TEM, has been modeled using a polydisperse Percus–Yevick hard sphere fluid model to obtain the interparticle interference contribution to the scattered intensity. By combining this modeling with quantitative TEM and SAXS invariant analysis, the structure of the micelles as a function of the molecular parameters can be completely characterized. In addition, a transition from liquid‐like to an ordered simple cubic arrangement of micelles has been observed upon increasing the copolymer concentration.

Improving adhesion of wood fiber with polystyrene by the chemical treatment of fiber with a coupling agent and the influence on the mechanical properties of composites

Abstract: —The mechanical properties of polystyrene filled with chemithermomechanical pulp and wood residues of softwood and hardwood species, which were precoated with phthalic anhydride and various polymers, e.g. polystyrene and PVC, have been investigated. The extent of improvement in the mechanical properties of the composite materials depends on the coating composition, the concentration of phthalic anhydride, the nature of the coated polymers, as well as the concentration of fiber, the nature of the wood species, and the nature of the pulps. Experimental results indicate that phthalic anhydride acts as a coupling agent, but when its performance was compared to that of poly[methylene (polyphenyl isocynate)], it seemed inferior to the latter.

The effects of flow on miscibility in a blend of polystyrene and poly(vinyl methyl ether)

Abstract: Shear and extensional flows can have a significant effect on the miscibility for a blend of polystyrene with poly(vinyl methyl ether). The cloud point temperature in a planar stagnation flow is elevated by as much as 12 K; the magnitude depends on the extension rate, the strain, and the blend composition. Flow-induced miscibility is also observed in the shear flow between parallel plates which has been used to test smaller samples and to prepare solid samples for further characterization. At lower temperatures, as much as 30 K below the coexistence temperature, flow-induced phase separation occurs in both shear flow and extensional flows. The stress, rather than deformation rate, appears to be the most important parameter in flow-induced phase separation.

Thermoplastic composties of polystyrene: Effect of different wood species on mechanical properties

Abstract: Both softwood (spruce) and hardwood (aspen and birch) species in the form of different pulps (e.g., sawdust, chemithermomechanical pulp, explosion pulp and OPCO pulp) have been used (10–40 wt% composite) as reinforcing fillers for thermoplastic composites of polystyrene. Mechanical properties, are examined, e.g., tensile modulus, tensile strength at maximum point, and the corresponding elongation and energy as well as impact strength of compression molded composites. To improve the compatability of wood fibers which are hydrophilic and the polymer matrix which is hydrophobic, poly[methylene(polyphenyl isoeyanate)] (2 and 8 wt % of polymer) was used as a coupling agent. The mechanical properties of the treated composites are improved up to 30% in fiber content whereas a downward trend for untreated composites was observed when an increase in fiber content occurred. The overall improvements in mechanical properties due to the addition of isocyanate can be explained by the linkage of isocyanate molecules with fiber matrix through the chain of covalent bonds and the interaction of π-electrons of benzene rings of polystyrene as well as isocyanate. As a result, poly[methylene(polyphenyl isocyanate)] forms a bridge between fiber and polymer on the interfaces. This result is instrumental for efficient stress transfer between cellulose fibers and thermoplastics. The performance of different pulps of various wood species as reinforcing fillers for thermoplastic composites is also examined.

Use of the D(3He,P)4 He reaction to study polymer diffusion in polymer melts

Abstract: By measuring the diffusion coefficient of a deuterated polystyrene in a hydrogenated polystyrene, we demonstrate the use of the D(3He,p)4He reaction to profile deuterium in polymers. Evaluation of the technique shows that with a 3He beam energy of 2 MeV, the beam at normal incidence to the sample and a detector angle of 160°, depths of 8 μm can be profiled, with a resolution of 390 nm at the surface and 420 nm at 8 μm. At the other extreme with a beam energy of 0.7 MeV and a glancing angle of incidence of 15° a resolution of 30 nm can be achieved at depths of up to 0.2 μm. The capability of the technique is compared with the ion beam technique more commonly used for profiling deuterium: elastic recoil detection analysis.

Anionic synthesis of chain‐end functionalized polymers using 1,1‐diphenylethylene derivatives. Preparation of 4‐hydroxyphenyl‐terminated polystyrenes

Abstract: A new, general functionalization reaction for polymeric organolithium compounds was developed based on their quantitative reaction with 1,1-diphenylethylene derivatives. The utility of this method was demonstrated by preparation of 4-hydroxyphenyl-terminated polystyrene (2b) by reaction of polystyryllithium in benzene at room temperature with 1-[4-(tert-butyldimethylsiloxy)phenyl]-1-phenylethylene (1a) followed by hydrolysis with dilute hydrochloric acid. The course of the functionalization reaction was monitored by ultraviolet-visible spectroscopy at 406 nm. Polystyrene 2b was characterized by size exclusion chromatography, thinlayer chromatography, membrane osmometry, end-group titration and both 1H and 13C NMR spectroscopy. All experimental evidence is consistent with quantitative functionalization via the 1,1-diphenylethylene derivative.

Isotropic microporous syndiotactic polystyrene membranes and processes for preparing the same

Abstract: This invention relates to semi-permeable isotropic syndiotactic polystyrene microporous membranes and processes for preparing such membranes.

Silver coated latex spheres

Abstract: Polystyrene (PS) and poly-methylmethacrylate (PMMA) particles have been coated with a silver shell from silver salt solutions by chemical reduction. The resulting colloidal particles exhibit absorption spectra which are red-shifted and broadened, as compared to the absorption of homogeneous silver particles of the same size. A simple self-consistent calculation of the polarization of a coated sphere is presented. The absorption spectrum and the enhanced optical field in the dielectric core of the particles are calculated. Enhanced Raman signals of the polystyrene material enclosed by the silver shell are observed; the measured intensities are compared with calculated enhancement factors.

Dynamic light-scattering studies of polymer diffusion in porous materials: linear polystyrene in porous glass

Abstract: Relation entre la masse moleculaire et le coefficient de diffusion translationnelle, dans trois verres differents, de solutions diluees de polystyrene dans un bon solvant

Enthalpy relaxations in polymer blends and block copolymers: Influence of domain size

Abstract: It is now well known that enthalpy relaxation measurements can be used to establish polymer-polymer blend phase behavior when the glass transition temperatures of the two polymers are virtually coincident. In the most simple cases, the aging kinetics of an immiscible blend will be representative of the pure polymers superimposed upon each other. However, in many cases the situation is more complicated because of the presence of interface material. In this paper the relation between enthalpy recovery peak separation, domain size and interface thickness is considered. The discussion is based on relaxation experiments involving di-block copolymers of styrene and 2-vinyl pyridine, blends of polystyrene and poly(2-vinyl pyridine) and blends of poly(vinyl chloride) and poly(isopropyl methacrylate). If the amount of material in the interface is too large due to either a small average domain size or a thick interface no peak separation will occur. The first situation is found for the microphase separated block copolymer system whereas the second possibility occurs for blends of polymers which are on the verge of miscibility like poly(vinyl chloride) and poly(isopropyl methacrylate).

Effect of thermal treatments on the structure of syndiotactic polystyrene

Abstract: Syndiotactic polystyrene films were prepared from the melt with different thermal treatments. Amorphous or crystalline films were obtained; x-ray analysis shows that in the crystalline samples two crystalline forms can be present and that the phase composition depends on the thermal conditions. The two forms show a different stability to liquid methylene chloride, one being stable while the other can be dissolved or transformed to a completely different crystalline structure. In all the analyzed samples the study of transport properties of CH2 Cl2 at low activity indicates that the amorphous component behaves as atactic polystyrene. This allows the determination of the crystallinity in the different samples.

Dielectric properties of cleaned and monodisperse polystyrene latexes in microwaves

Abstract: The dielectric behavior (e′, e″) of three well-cleaned monodisperse polystyrene latexes having the same particle size and the same number of chemically-bound surface groups has been studied at a fixed microwave frequency (94 GHz), as a function of temperature and surface group (SO 4 − , COO−, OH) A large dielectric relaxation was observed in the sulfate-stabilized latex, which has the most polar surface end-group The anomalous behavior in the thermal dependence of the hydroxyl and carboxyl-stabilized latexes (the OH latex being more pronounced than the COO− latex) may originate from differences in the experimental conditions used for the preparation of such polymer colloids, or due to the presence of ionic species On the basis of various dielectric models, the apparent volume fractions of the latexes were calculated The amount of “bound” water around the latex particle was quantitatively correlated to the polarity of surface end-group (SO 4 − > COO− > OH) The differences between the calculated and actual values were not only a reflection of the thickness of vicinal water, but could also be indicative of the presence of oligomeric species in the suspension's medium (serum) of the latex The permittivities of hydrated particle and of “bound” water were obtained with a non-linear iterative procedure