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PubMed2004

Heterogeneity in styrene-butadiene latex films.

Low-Tg styrene-butadiene (SB) latex films were investigated by noncontact atomic force microscopy and scanning electric potential microscopy, revealing a number of different morphologies and electric potential patterns across films cast from the same SB latex dispersions under the same conditions. Surface leveling and charge dispersion throughout the films are, thus, restrained even at temperatures above Tg and the minimum film-formation temperature. An unprecedented electric pattern is observed, in which the particle cores are more positive than the contacting particle outer layers. Different packing patterns, including cubic and hexagonal arrays, coexist in neighboring areas. Zonal centrifugation of the SB latex in sucrose density gradient shows that particles cover a broad range of densities. Thus, film surface heterogeneity is at least partly due to particle heterogeneity. Fractal dimensions of topographic profiles are lower than those of the electric potential profiles, showing that charge mobility is much more restrained than polymer chain motion at the film surface and that it imposes a limit to the charged chain-ends motion.

Butadienes↗
PubMed2005

Improved methodology to measure surface tension and its application to polystyrene or poly(methyl methacrylate) in styrene solutions.

Several methods to measure surface tension involve some inconveniences when applied to moderate or highly viscous polymer solutions. Therefore, an improved version of the weight drop method (WDM) is proposed here. In addition, a comparative analysis of methods is carried out, including the drop profile (DPM), the selected planes (SPM), the WDM and the one proposed here (WDSM), finding that the WDSM is as easy to apply as the SPM and the WDM, although in practical conditions it is much more accurate than either of them. Moreover, the WDSM allows to reproduce the results that can be obtained using DPM, but, in general, it is much easier to implement and apply than such method. The WDSM was used to determine surface tension in polystyrene or poly(methyl methacrylate) in styrene solutions, where the dependence of such property with polymer average molecular weight and polymer concentration was experimentally evaluated.

Molecular Weight↗
PubMed2006

Enantioconvergent hydrolysis of styrene epoxides by newly discovered epoxide hydrolases in mung bean.

[reaction: see text] Two novel epoxide hydrolases were discovered in mung bean (Phaseolus radiatus L.) for the first time, either of which can catalyze enantioconvergent hydrolysis of styrene epoxides. Their regioselectivity coefficients are more than 90% for the p-nitrostyrene oxide. Furthermore, the crude mung bean powder was also shown to be a cheap and practical biocatalyst, allowing a one-step asymmetric synthesis of chiral (R)-diols from racemic epoxides, in up to >99% ee and 68.7% overall yield (after recrystallization).

Catalysis↗
PubMed2004

Enantio- and diastereocontrol in intermolecular cyclopropanation reaction of styrene catalyzed by dirhodium(II) complexes with bulky ortho-metalated aryl phosphines.

Enantiomerically pure dirhodium(II) complexes with ortho-metalated p-substituted aryl phosphines have been shown to be enantio- and diastereoselective in the cyclopropanation of styrene by ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylate.

Catalysis↗
PubMed2004

Is styrene planar in liquid phases?

The proton NMR spectra of two (13)C-labeled isotopomers of styrene dissolved in two liquid crystalline solvents have been obtained and analyzed to yield four sets each of 24 dipolar couplings. These couplings were then used to investigate the structure of the ring and the ene fragments of the molecule, and the position of the maximum, phi(0), in the ring-ene bond rotational probability distribution. To do this, the effect on the dipolar couplings of small-amplitude vibrational motion was taken into account using vibrational wave functions calculated by molecular orbital and density functional methods. It is concluded that the NMR data are consistent with the ring fragment, averaged over the ring-ene rotation, planar, while the ene fragment is not. The value of phi(0) is found to be 18.0 degrees +/-0.2 degrees for the two solutions, compared with a value of 27 degrees calculated by the molecular method MP2/6-31G(*).

Carbon Radioisotopes↗
PubMed2004

Highly enantioselective epoxidation of styrenes: implication of an electronic effect on the competition between spiro and planar transition states.

Asymmetric epoxidation of various styrenes using carbocyclic oxazolidinone-containing ketone 3 has been investigated. High enantioselectivity (89-93% enantiomeric excess) has been attained for this challenging class of alkenes. Mechanistic studies show that substituents on the ketone catalyst can have electronic influences on secondary orbital interactions, which affects the competition between spiro and planar transition states and, ultimately, enantioselectivity. The results described herein not only reveal the potential of chiral dioxirane catalyzed asymmetric epoxidation as a viable entry into this important class of olefins but also further enhance the understanding of the mechanistic aspects of chiral ketone-catalyzed asymmetric epoxidation.

Epoxy Compounds↗
PubMed2006

Examination of styrene-divinylbenzene ion-exchange resins, used in contact with food, for potential migrants.

The nature of extractable substances from five types of styrene-divinylbenzene ion-exchange resins used in the preparation of foodstuffs was investigated. Strong acid cation resins, strong and weak base anion resins, and an active carbon replacement resin were examined. These resins are used for a variety of purposes including water softening, decalcification of sugar syrups, demineralization, removal of nitrate ions from water and decolourization. Analysis was carried out using electrospray LC-MS- and GC-MS-based methodologies. Extractable substances from new resins were identified as mainly being by-products of the resin manufacturing process. Levels of extractable substances decreased with washing.

Chromatography, Liquid↗
PubMed2000

Field investigation comparing diffusion badge and charcoal tube monitoring for styrene.

A short investigation was completed to compare organic vapor monitor and charcoal tube results for airborne styrene in three fiberglass boat manufacturing plants. Time-weighted average results were compared for 15 paired samples (12 breathing zone/3 area). Linear regression analysis showed a strong predictive relationship and an R2 value of 0.96. The organic vapor monitors had 31 percent higher results than the charcoal tubes across the range of concentrations 5.6 ppm to 150 ppm. Paired t-test validated this inference by demonstrating statistically significant differences between the means.

Air Pollutants, Occupational↗
PubMed2002

The catalytic incineration of styrene over an Mn2O3/Fe2O3 catalyst.

In this study, styrene monomer (SM) was treated by a commercial catalyst, Mn2O3/Fe2O3, in a fixed-bed reactor. The study can be classified into two major parts. First, the effects of operating factors, such as temperature, SM concentration, space velocity, and O2 concentration, on the performance of the catalyst were investigated. Second, two catalyst life tests were carried out to characterize the deactivation effect of SM. The results show that the catalyst results in higher conversion of SM at a higher inlet temperature and higher O2 concentrations. The conversion of SM decreases with increasing SM concentration and space velocity. From the statistical analysis of the data, we find that temperature is the most important factor on the catalytic incineration. Oxygen concentration, SM concentration, and space velocity are significant parameters as well. This paper also provides information on the deactivation effect of SM. The catalysts were characterized by surface and pore-size analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron spectroscopy for chemical analysis (ESCA) before and after the tests. The results show that the catalytic deactivation may be caused by carbon coating, and the pore size and surface area of the catalyst are smaller after deactivation.

Air Pollution↗
PubMedDate not supplied

Measuring performance of a half-mask respirator in a styrene environment.

A workplace protection factor (WPF) study was conducted with a half-mask air-purifying respirator during fiber glass boat production. Styrene was the measured analyte, and the geometric mean WPF found was 39.7. Analytical detection limits, sample contamination, and pulmonary elimination from previous exposures or from skin absorption were identified as important considerations that can bias the WPFs measured. There were significant differences in the mean concentrations found inside the respirator when analyzed by time period. An increase in the concentration found inside the facepiece cavity and a decrease in the WPF over time was found for people with three or four measurements. This indicates either a change in performance of the respirator over time or a bias from low-level exposures during the day or skin absorption.

Air Pollutants, Occupational↗
PubMed2004

Historical estimation of exposure to 1,3-butadiene, styrene, and dimethyldithiocarbamate among synthetic rubber workers.

Quantitative estimates of exposure to 1,3-butadiene (BD), styrene (STY), and dimethyldithiocarbamate (DMDTC) were developed for a follow-up study of workers at six North American synthetic rubber plants. Procedures entailed identifying tasks and jobs involving exposure, identifying factors influencing historical changes in exposure potential, and using mathematical models to calculate job- and time-period-specific exposures. Exposure metrics included 8-hour time-weighted average (TWA) intensity, the annual number of peak exposures (BD: >100 ppm, STY: >50 ppm) and TWA intensity below and above the peak threshold. The 5th and 95th percentiles of the approximate probability distribution of each exposure estimate served as its 90% uncertainty interval. Job- and year-specific estimates were linked with subjects' work histories to obtain cumulative exposure indices. Exposure estimates varied among tasks, jobs, plants, and time periods. BD TWAs were approximately 10 ppm during the 1940s-1960s and declined during the 1970s and 1980s. STY TWAs were always <2 ppm. DMDTC exposure began in the 1950s, was high through the 1960s, and later declined. BD peak exposure accounted for a large proportion of cumulative BD exposure, whereas almost none of the STY exposure was experienced at levels >50 ppm. Exposure indices were correlated. Exposures were higher than previously estimated. Multiple correlations among DMDTC, BD, and STY exposure estimates make it difficult to estimate agent-specific effects. Limitations of the methodology include the potential inaccuracy of the estimates, the lack of adequate industrial hygiene data to validate the estimates, the additional inaccuracy of linkage with poorly specified job groups, and the potential for differential exposure misclassification because the jobs and work areas where excess leukemia mortality occurred were well-known at the time of this study. Nevertheless, the new exposure estimates were highly correlated with the old, yielding equivalent exposure ranking of workers and were comparable to limited industrial hygiene data published by NIOSH.

Butadienes↗
PubMed1980

The effect of maternally inhaled styrene on embryonal and foetal development in mice and Chinese hamsters.

Pregnant mice and Chinese hamsters were exposed to styrene 6 hrs daily during the period of major organogenesis via inhalation in concentrations 250 p.p.m., and 300, 500, 750 and 1000 p.p.m., respectively. Both in mice and in Chinese hamsters embryotoxicity was raised. Some minor skeletal malformations (rib fusions, extra ribs) were noted in mice but not in Chinese hamsters.

Animals↗
PubMed1981

Changes in the c-wave of the electroretinogram and in the standing potential of the eye after small doses of toluene and styrene.

Low and moderate i.v. doses of toluene or styrene dissolved in a lipid emulsion (Intralipid) were given to cynomolgus monkeys. The d.c. ERG and the standing potential (SP) of the eye were recorded directly with corneal contact lenses, very stable calomel electrodes and under very constant general anaesthesia. Even small doses of the solvents, corresponding approximately to the Swedish hygienic threshold limit values for these solvents in air, clearly provoked slow variations with time in the amplitude of the c-wave of the ERG and in the SP level. Both potentials are generated mainly in the pigment epithelium. It is suggested that the effects reflect a direct influence of the solvents upon i.a. the cell membrane or the metabolism of the pigment epithelium.

Animals↗
PubMed1999

Lymphatic and haematopoietic cancer mortality in a population attending school adjacent to styrene-butadiene facilities, 1963-1993.

STUDY OBJECTIVE: To evaluate the risk of mortality from lymphatic and haematopoietic cancers and other causes among students. DESIGN: The study used school records, yearbooks, and Texas Department of Health records for the school years 1963-64 to 1992-93 to construct a cohort of 15,403 students. Three mortality databases were searched to identify deaths, and mortality rates in the cohort were compared with mortality rates from the United States and Texas. Computed standardised mortality ratios and 95% confidence intervals were used. SETTING: Eastern Texas high school adjacent to facilities that have been producing synthetic styrene-butadiene since 1943. MAIN RESULTS: 338 deaths were identified. The all causes standardised mortality ratio was 0.84 (95% confidence intervals 0.74, 0.95) for men and 0.89 (0.73, 1.09) for women. The standardised mortality ratio for all lymphatic and haematopoietic cancers was 1.64 (95% confidence intervals 0.85, 2.87) for men and 0.47 (0.06, 1.70) for women. The slight male excess in lymphatic and haematopoietic cancers was stronger among men who attended school for two years or less. CONCLUSIONS: The overall mortality from lymphatic and haematopoietic cancer among the students was little different from that of the United States as a whole. A moderate excess for men, predominantly among the shorter-term students, was offset by a deficit among women. These variations are compatible with random fluctuations; the overall pattern is not indicative of an effect of environmental exposure sustained while attending the high school.

Adult↗