Low Molecular Weight Polystyrene Research Articles

Assessment of Polystyrene Extract for Estrogenic Activity in the Rat Uterotrophic Model and an in Vitro Recombinant Receptor Reporter Gene Assay

The purpose of the study was to determine whether polystyrene used in food-contact applications would elicit an estrogenic response when extracts simulating exaggerated conditions of use were subjected to in vivo and in vitro tests. A sample of polystyrene was subjected to extraction conditions that simulate, or exaggerate, the actual food-contact uses of polystyrene to maximize the amount of low molecular weight polystyrene extractables. the food-simulating solvent and the time and temperature conditions recommended by the Food and Drug Administration (FDA) were selected to maximize the level of extractable components from polystyrene. the extract was examined for its estrogenic response in vivo using the immature rat uterotrophic assay and in vitro using an estrogen receptor (ER)-mediated recombinant receptor reporter gene assay. in vivo, the uterine weights of juvenile female Sprague Dawley® rats (10 rats/group) were determined after oral gavage exposure to the extract (two dosage levels: one represents the maximum potential daily human exposure to polystyrene extractables and the other represents one-tenth of the maximum exposure level), vehicle control (sesame oil), or positive control [diethylstilbestrol (DES), at 200 äg/kg body weight]. in addition, five treatment groups were dosed by subcutaneous injection of either estradiol (1, 50, and 500 äg/Kg body weight) or DES (2 and 200 äg/kg body weight). Dosing began on postnatal day (pnd) 21 and continued daily through pnd 23. Body weights were collected at study initiation (pnd 21) and at necropsy (pnd 24). Body weights were not different statistically between treatment groups at study initiation or at necropsy. Uterine wet weights and uterine weights relative to body weights were significantly increased (p<0.05) for estradiol at 50 and 500 äg/kg, DES at 2 and 200 äg/kg, and DES at 200 äg/kg (oral) over vehicle control. the polystyrene extract had no effect on uterine wet weight or uterine weights relative to body weights at either level tested.An in vitro recombinant estrogen receptor/reporter gene assay that involved transiently transfecting MCF-7 human breast cancer cells with the chimeric human ER, Ga14-HEGO, consisting of the yeast Ga14 DNA binding domain linked to the ligand binding domain of the human ER and a Ga14 response element (17mer)-regulated reporter gene (17m. 5-G-Luc) was employed. Dose-dependent induction of the reporter gene, 17m5-G-Luc, was observed with the positive control, 17β-estradiol (E2). Induction of greater than 100-fold was obtained following incubation of transfected MCF-7 cells with 10 nM E2 for 24 hours. No induction of reporter gene activity was observed with the polystyrene extracts dissolved in dimethylsulfoxide (0.01, 0.1 or 0.01 mg/ml) using the same assay conditions. These results indicate that polystyrene extract does not elicit ER-mediated activity using the Ga14-HEGO/17m. 5-G-Luc recombinant receptor/reporter gene assay.In conclusion, extracts from polystyrene produced no estrogenic response in either the rat uterotrophic assay or the MCF-7 cell assay for estrogen receptor-mediated activity.

Order−Disorder Transition, Microdomain Structure, and Phase Behavior in Binary Mixtures of Low Molecular Weight Polystyrene-block-polyisoprene Copolymers

Order-disorder transition, microdomain structure, and phase behavior in binary mixtures of low molecular weight polystyrene-block-polyisoprene (SI diblock) copolymers were investigated. For the study, four SI diblock copolymers were synthesized, namely (i) SI-Q having a weight-average molecular weight (Mw )o f 2.810 4 and polystyrene volume fraction (f) of 0.186, (ii) SI-R having Mw ) 1.5 10 4 and f ) 0.508, (iii) SI-S having Mw ) 1.76 10 4 and f ) 0.372, and (iv) SI-M having Mw ) 1.55 10 4 and f ) 0.626. Then binary mixtures of SI-Q and SI-R and binary mixtures of SI-M and SI-S, with various compositions, were prepared via solvent casting. The order-disorder transition of the binary mixtures was investigated using rheology and small-angle X-ray scattering (SAXS), respectively. Also investigated was the microdomain structure of the binary mixtures using SAXS and transmission electron microscopy (TEM). Experimentally determined phase diagrams are compared with predictions based on a self- consistent mean-field theory.

Viscoelastic Properties of Amorphous Polymers. 7. Changes of the Anomalous Behavior of Low Molecular Weight Polystyrene with the Addition of a Diluent

Torsional shear measurements of the recoverable creep compliance of a 54.7% solution of a narrow molecular weight distribution polystyrene of low molecular weight, 4000, in tri-m-tolyl phosphate ar...

Dielectric Study of Miscibility in Weakly Segregated Polymer Blends

Miscibility of polymer blends around the critical solution temperatures was studied by using a dielectric method for the system composed of low molecular weight cis-polyisoprene (cis-PIp) and polystyrene (PSt) and the system of cis-PIp and vinylpolyisoprene (vinyl-PIp). All these polymers exhibit the dielectric relaxation due to the segmental mode and cis-PIp also exhibits the normal mode relaxation. In the cis-PIp/PSt blend, the normal mode relaxation conformed to the blending law, indicating that the blend is homogeneous over a length scale of the end-to-end distance. On the other hand the cis-PIp/vinyl-PIp system exhibited a complex loss curve mainly due to the segmental mode of vinyl-PIp. The shape of the loss curve varied with temperature, indicating that the blend is weakly segregated and that the degree of inhomogeneity of the length scale of the monomeric unit varies with temperature.

Thiol-ended polyethylene oxide as reactive stabilizer for dispersion polymerization of styrene

Radical dispersion polymerization of styrene in aqueous ethanol solutions was performed in the presence of a new reactive polyethylene oxide stabilizer with thiol end groups. This reactive stabilizer was compared to the more conventional poly (N-vinyl pyrrolidone). Particles size distribution, molecular weights and kinetics were investigated. Monodispersed polymer particles with diameter in the range 200–2000 nm were obtained depending on the amount of stabilizer used. In all cases, the polyethylene oxide (PEO) sequence of the dispersant was partly incorporated at the surface of the latex particles, but the grafting yield of polyethylene oxide chains was always limited and did not exceed 15%. Part of the stabilizer being unreacted or reacted with low molecular weight polystyrene remained in the continuous phase.

Enzymatic degradation of polystyrene by hydroquinone peroxidase of Azotobacter beijerinckii HM121

The hydroquinone peroxidase of a lignin decolorizing bacterium, Azotobacter beijerinckii HM121 degraded a water-insoluble synthetic polymer, polystyrene, in a two-phase system (dichloromethane-water), in which it was degraded in dichloromethane to small water-soluble molecules in a short time in the presence of hydrogen peroxide and tetramethylhydroquinone. Two grams per liter of polystyrene ( M r 935,000) in the dichloromethane phase was completely transferred to the water phase in 5 min by the enzymatic reaction. The degradation products in the water phase were initially detected at R f 0.6 ( M r 1,000) in thin layer chromatography after reacting for 5 min, and then at R f 0 ( M r 350) after reacting for 10 min. Another polystyrene ( M r 114,200) was degraded in a similar manner but low molecular weight polystyrene ( M r 760) was degraded and detected at R f 0 without producing intermediate products at R f 0.6 after 1-min reaction.

Study of mixed solvent quality in a polystyrene-dioctyl phthalate-polystyrene system

Polymer solvent interactions in the ternary system high molecular weight polystyrene (HMPS), low molecular weight polystyrene (LMPS), and dioctyl phthalate (DOP) have been characterized by means of intrinsic viscometry (IV), dynamic light scattering (DLS), and static light scattering (SLS). Excluded volume exponents have been extracted from the scaling of intrinsic viscosity and translational diffusivity with polymer molecular weight for a mixed solvent of 13 wt % LMPS/87 wt % DOP. The value of the excluded volume exponent, v = 0.45, indicates that HMPS in the mixed solvent DOP/LMPS has apparently assumed a reduced conformation relative to the theta condition. However, SLS measures of the second virial coefficient (A 2 ) confirm that DOP is a theta solvent at our experimental temperature of 22°C and indicate that the addition of LMPS increases A 2 . SLS also suggests that neither solvent component is strongly preferentially adsorped into the HMPS coil. Our system then is a mixture of a theta solvent and a good solvent that exhibits poor solvent scaling behavior. We believe this to be the first demonstration of such behavior in a system that does not exhibit appreciable preferential adsorption. We conclude by examining our observations in the context of current descriptions of mixed solvent thermodynamics.

Effect of Volume Fraction on the Order−Disorder Transition in Low Molecular Weight Polystyrene-block-polyisoprene Copolymers. 2. Order−Disorder Transition Temperature Determined by Small-Angle X-ray Scattering

Small-angle X-ray scattering (SAXS) was employed to investigate the order−disorder transition of low molecular weight polystyrene-block-polyisoprene (SI diblock) copolymers with widely varying composition. The SI diblock copolymers investigated in the present study have molecular weight varying from 15 000 to 41 000 and the volume fraction of PS block varying from 0.186 to 0.811. Low-temperature resolution SAXS experiments, which involved a temperature increment of ≥10 °C, did not allow us to accurately determine the order−disorder transition temperatures (TODT) of the SI diblock copolymers, but high-temperature resolution SAXS experiments, which involved measurements of the scattering profiles across TODT with a small temperature increment of ≤1 °C, enabled us to determine the values of TODT with accuracy to within ±1 °C. TODT was determined to be the temperature at which the reciprocal of the maximum intensity and the square of the half-width at half-maximum of the first-order scattering maximum change discontinuously with the reciprocal of absolute temperature. We compared the values of TODT determined from SAXS experiments with those determined from rheological measurements reported in part 1 of this series.

CO2-Enhanced Diffusion of Azobenzene in Glassy Polystyrene near the Glass Transition

Forced Rayleigh scattering (FRS) has been used to measure the tracer diffusion coefficient of azobenzene in low molecular weight polystyrene (PS) as a function of temperature, and in high molecular weight PS plasticized by CO2 at 35 °C and CO2 pressures from 14 to 85 bar. In contrast to dye diffusion in pure PS and PS plasticized by tricresyl phosphate, where the effect of plasticization by temperature, chain ends, or added diluent can be accounted for by (T − Tg) scaling, dye diffusion in CO2-plasticized PS is enhanced by 2−3 orders of magnitude over values predicted on the basis of Tg depression alone. This enhancement begins at surprisingly low CO2 pressures (<15 bar at 35 °C) and is maintained across the CO2-induced glass transition. A large difference in mobilities of the cis and trans isomers of azobenzene is also observed in the presence of CO2, which is much greater than that seen in the experiments on pure PS. Two additional FRS relaxation modes unrelated to translational diffusion of the dye molecules have been identified in this study: a fast, local relaxation attributed to dye rotation, and a slow relaxation attributed to the dynamic response of the PS/CO2 matrix to a chemical potential driving force associated with the azobenzene isomers.

The molecular basis of fracture in polystyrene films: Role of molecular weight

AbstractThe molecular basis for fracture was examined using a custom‐built Dental Burr Grinding Instrument, which cuts at a depth of 500 nm per pass. A direct miniemulsification method was used to form uniform‐sized latex particles from narrow molecular weight distribution, anionically synthesized polystyrenes. Several polystyrenes were examined as a function of molecular weight, and blends were made of high and low molecular weight polystyrenes. In addition, a broad molecular weight polystyrene was included for comparison. These latexes were dried and cleaned, and molded under mild conditions, followed by annealing for various lengths of time at 144°C. The Dental Burr Grinding Instrument measures the total energy required to fracture the sample. The total number of chains undergoing scission per unit volume was determined via GPC before and after the fracture process. Using an energy balance approach, the total number of chains undergoing pullout (from either side of the fracture surfaces) was estimated. In order to obtain a broader picture of the process, data collected by Mohammadi et al., and by Sambasivam et al., were integrated into the analysis. Basically, at very low molecular weights, ca. 32,000 g/mol, substantially 100% pullout occurs. At the midmolecular weight range, about 150,000 to 180,000 g/mol, chain scission and chain pullout contributions to the total energy are approximately equal. For very high molecular weights, the chain scission contribution is about 90%. A scaling relationship is proposed between the molecular weight of the polymer and the fraction of chains undergoing scission. © 1995 John Wiley &amp; Sons, Inc.

Solid state NMR investigation of antiplasticization of polystyrene by mineral oil

AbstractThe effects of mineral oil plasticization of polystyrene were investigated as a function of polystyrene molecular weight and mineral oil concentration. Solid state NMR, thermo/mechanical methods and positron annihilation spectroscopy (PAS) were used to study the molecular dynamics and free volume effects of this blend. Antiplasticization was observed in the low (40,000) molecular weight polystyrene samples as an embrittlement of the system. In contrast, the flexural modulus was not affected by the presence of mineral oil in the higher (270,000) molecular weight polymers but a decrease in the flexural strength was observed with increasing mineral oil concentration. The NMR and PAS data indicated that the mineral oil was not dissolved in the polymer at ambient temperature, rather it phase separated even at very low concentrations. This caused antiplasticization in low molecular weight polymers because the small free volume holes were filled causing a densification of the system. With high molecular weight polystyrene, this phase separation was manifested as a decrease in the flexural strength.

Determination of Sharpness of Order-Disorder Transition of Block Copolymers by Scattering Methods

It has been considered that elastic scattering profiles gradually change with temperature across the order-disorder transition (ODT) of block copolymers and hence a unique determination of the ODT temperature ( T ODT ) is difficult by scattering methods alone. We report here our finding that the scattering experiments with a high temperature-resolution, involving a temperature increment of smaller than or equal to 1°C, enables a straightforward, unequivocal determination of T ODT even for a low molecular weight polystyrene- block -polyisoprene copolymer. Moreover we found that the high temperature-resolution scattering experiment can reveal the very sharp ODT of the copolymer occurring in a very narrow temperature range of less than 1° C; the experimental results with a low temperature-resolution can easily lead us to overlook the sharpness of the ODT and to misunderstand the nature of the transition.

Specular and Off-Specular Neutron Reflectivity of a Low Molecular Weight Polystyrene Surfactant at the Air-Water Interface

Neutron reflectivity measurements were made on films at the air-water interface of a highly characterized low molecular weight polystyrene surfactant, with a single hydroxyl end group. The II-A isotherm is consistent with collapse of a classical fluid surfactant monolayer to a trilayer structure at high compressions. Before the collapse point, reflectivity measurements indicated a decrease in the average tilt angle of the molecules to the surface normal as the layer was compressed. After the collapse point, the film structure was time dependent and was best represented by a monolayer of constant thickness at the water interface, covered by a bilayer whose thickness increased with time and a time-dependent diffuse layer above the bilayer. Multidetector reflectivity profiles showed only specular reflection for surface pressures below the collapse point, but in the collapse region, some off-specular reflection was clearly present, indicating the presence of surface texture on the micron length scale in the plane of the interface. This is believed to be the first observation of well-developed off-specular neutron reflection from a Langmuir film.

Viscoelastic properties of amorphous polymers. 2. Anomalous temperature dependence of the steady-state recoverable compliance in low-molecular-weight polymers

Previous study of the viscoelastic behavior of low molecular weight polystyrenes found that the steady-state recoverable compliance, J e o , decreased markedly with temperature as the T g was approached from above. This anomalous viscoelastic property of polystyrene was explained by a model of coupled molecular motions. Application of the coupling model to low molecular weight polyisobutylene (PIB) leads to the prediction that the anomalous marked decrease of J e o will not be observed in PIB. This prediction made for the behaviour of PIB was verified by new creep recovery measurements.

THERMAL OXIDATION OF POLYMER BLENDS CONTAINING AN ANTIOXIDANT

Abstract Thermal oxidation of blends of polystyrene and poly(vinyl methyl ether) containing a hindered phenol as antioxidant was studied at 110°C. The incorporation of the antioxidant in the miscible blend lengthens the induction period and lowers the rate of oxidation. Phase separation which preceded the end of the induction period caused the antioxidant to redistribute itself among the different phases. This in turn controlled the induction period and the oxidation rate. The molecular weight of the PVME component in the blend remained unchanged during the induction period but decreased rapidly afterwards. Polystyrene also underwent chain scission after the end of the induction period. When low molecular weight polystyrene was blended with PVME, the films remained homogeneous throughout the oxidation reaction. This resulted in a further increase in the induction period and decrease in the rate of oxidation.

Depolarized Rayleigh scattering from short-chain polystyrene in a .THETA.-solvent

Depolarized Rayleigh spectra of low molecular weight polystyrene samples in dilute solution in bicyclohexyl, a θ-solvent at 61°C, were obtained. The spectra fit well to single Lorentzian line shapes which were assigned to the overall reorientation motion of the highly anisotropic polymer. The relaxation times at different molecular weights scale with the Stokes-Einstein-Debye equation. The obtained hydrodynamic volumes reduced to a simple monomer unit, show a maximum at w ≃ 2000, apparently reflecting increasing coiling with increasing chain length

Analysis of Low Molecular Weight Polymers with Gel Permeation Chromatography

Abstract Intrinsic viscosities and gel permeation chromatography (GPC) elution times were determined in toluene on commercially available standards of polystyrene (PSTY) and polymethyl methacrylate (PMMA) having Mn in the range of 103 to 105 and 104 to 106, respectively. In addition, elution times were determined on the discrete GPC peaks of dimer, trimer, tetramer, etc. as seen in lower molecular weight PSTY and PMMA. Intrinsic viscosities of oligomers were estimated by extrapolation of the Mark-Houwind-Sakurada equations determined from our data, and the results were used to establish a universal calibration curve over a wide range of molecular weights. A similar approach was taken by using literature data for the intrinsic viscosities of PSTY and PMMA in tetra-hydrofuran. It was verified by proton NMR that the universal calibration curve so constructed is useful at Mn, values as low as 300. No correction was necessary for chain length dependence of the detector response.

Diluent effects on viscoelastic behavior

The effects of dilution upon the viscoelastic behavior of polymers are discussed and the related results of two investigations on solvent effects are presented. The creep behavior of a 40% polyvinylacetate (PVAc) solution where the solvent, sucrose benzoate, has a higher glass temperature than the PVAc is presented. Since the glass temperature, T g, of the solution is between that of the polymer and the solvent, it is higher than that of the neat polymer. In the second study, the viscosity and the recoverable compliance of six molecular-weight bimodal blends of a high (3.8×10 6) and a low (1.03×10 4) molecular-weight polystyrene were determined. The low molecular-weight component played the role of a Flory theta solvent at long times at all temperatures, enabling the determination of the steady-state recoverable compliance, J e o , of the high-molecular components as a function of concentration under theta conditions. Retardation spectra were determined from the reduced shear compliance curves for all the solutions and the neat components.

The use of substituted allylic sulfides to prepare end-functional polymers of controlled molecular weight by free-radical polymerization

Substituted allylic sulfides were utilized as chain-transfer agents to prepare low molecular weight polystyrene and poly(methyl methacrylate) capped with carboxy, hydroxy, trialkoxysilyl, or amino groups. Low molecular weight α,ω-dicarboxypolystyrene or poly(methyl methacrylate), α-hydroxy-ω-carboxy- and α,ω-dihydroxy-terminated polystyrene, poly(methyl methacrylate), and poly(butyl acrylate) and polymers terminated at one end with hydroxy and at the other with a phthalamido group are prepared

Dynamic properties of low- and moderate-molecular-weight polystyrenes at infinite dilution

Oscillatory flow birefringence (OFB) has been used to determine the dilute solution and infinite dilution conformational dynamics properties of low molecular weight polystyrenes (PS) in Aroclor 1248. These results are well-described by the bead-spring model (BSM) of Rouse and Zimm. Pulsed-field-gradient NMR and forced Rayleigh scattering have been used to determine the infinite dilution diffusion coefficients for five PS samples in the same solvent. These results are well-represented by the Kirkwood-Riseman expression. The OFB and diffusivity results have been combined with other literature data for PS in Aroclor 1248 to provide a stringent test of the BSM