Vinylidene concentration

At the end of this time, no change could be observed in the vinylidene concentration, no hydroperoxide could be detected either by chemical analysis or by IR spectroscopy and no additional carbonyl was formed (31). On irradiation, vinylidene disappearence and carbonyl formation rates were identical to the control and the time to embrittlement was the same. 

Figure 12. Effects of metal chelates (0.025%) on vinylidene concentration during...

Some additional dyad fractions from the research cited in the last problem J are reported at intermediate feedstock concentrations (M = vinylidene chloride M2 = isobutylene) ... 

The following substances chloroform, carbon tetrachloride 1,1,2-trichloroethane, 1,1,2,2-tetratchloroethane 1,1,1,2-tetrachloroethane pentachloroethane, vinylidene chloride 1,1,1 -trichloroethane and any substance containing one or more of those substances in a concentration equal to or greater than 0.1% by mass, other than (a) medical products (b) cosmetic products Supply for use at work in diffusive applications such as in surface cleaning and the cleaning of fabrics except for the purposes of research and development or for the purpose of analysis... 

Figure 6. Partly assembled, 5-gallon, low density polyethylene liner in a corrugated carton. Liner is coated with poly(vinylidene chloride) (Saran) to block oxygen entry and prevent loss of aroma used for cola concentrate.

The dangers linked to unstable substances that are insoluble compared with those that are soluble are also concentration effects. This is the case for many polyperoxides. Even those that are soluble can detonate if their concentration exceeds a critical value eg 15% for the peroxide of vinylidene chloride. 

Some chemicals are susceptible to peroxide formation in the presence of air [10, 56]. Table 2.15 shows a list of structures that can form peroxides. The peroxide formation is normally a slow process. However, highly unstable peroxide products can be formed which can cause an explosion. Some of the chemicals whose structures are shown form explosive peroxides even without a significant concentration (e.g., isopropyl ether, divinyl acetylene, vinylidene chloride, potassium metal, sodium amide). Other substances form a hazardous peroxide on concentration, such as diethyl ether, tetrahydrofuran, and vinyl ethers, or on initiation of a polymerization (e.g., methyl acrylate and styrene) [66]. 

The IR-spectrum of the polymer was measured with a Nippon Bunko Model DS-403G infrared spectrometer. The concentration of the unsaturated groups in the polymer (number of unsaturated group per 1000 carbons) was determined from the absorbances at 966 cm l (trans-vinylene), 910 (vinyl) and 890 (vinylidene) in the IR-spectrum by the method reported by Cernia et al. (7). 

Toxicology. Vinylidene chloride (VDC) causes central nervous system (CNS) depression at high levels, and repeated exposure to lower concentrations results in liver and kidney damage in experimental animals. 

Vinylidene chloride is produced by the pyrolysis of 1,1,2-trichloroethane at 400°C in the presence of lime or base. Since both vinylidene chloride and vinyl chloride are carcinogenic, their concentrations must be kept low. 

The effect of pressure on polymerization, although not extensively studied, is important from the practical viewpoint since several monomers are polymerized at pressures above atmospheric. Pressure affects polymerization through changes in concentrations, rate constants, and equilibrium constants [Ogo, 1984 Weale, 1974 Zutty and Burkhart, 1962], The commercial polymerizations of most gaseous monomers (e.g., vinyl chloride, vinylidene chloride, tetrafluoroethylene, vinyl fluoride) are carried out at very moderate pressures of about 5-10 MPa (1 MPa = 145 psi), where the primary effect is one of increased... 

The double-bond composition varies in a complex manner with changes in metallocene and monomer concentrations because the orders of dependence of the various P-hydride transfer reactions on monomer and metallocene are not the same [Liu et al., 2001c Zhou et al., 2001]. Vinylidene content decreases with increasing monomer concentration, but increases with increasing metallocene. The trends for vinylene content are the opposite, while trisubstituted double-bond content is relatively unaffected by monomer and metallocene concentrations. 

There is not sufficient space to discuss all vinylidene complexes which have been reported, for example over 200 crystal structures are listed in the CCDC. Consequently, this article largely concentrates on the chemistry of metal vinylidene complexes which has been described since 1995. Vinylidene complexes are generally available for the metals of Groups 4—9, with several reactions of Group 10 alkynyls being supposed to proceed via intermediate vinylidenes. However, few of the latter compounds have yet been isolated. This chapter contains a summary of various preparative methods available, followed by a survey of stoichiometric reactions of vinylidene-metal complexes. A short section covers several non-catalytic reactions which are considered to proceed via vinylidene complexes. The latter, however, have been neither isolated nor detected under the prevailing conditions. 

Moreover, we confirmed the results previously ascertained through radiochemical measurements. In fact, the comparison between such data and those obtained by IR measurements on the atactic polymer fraction (Table IV) shows that the ratio between the number of polymeric chains with a —C2H6 end group (corresponding to a chain transfer process depending on the catalyst concentration) and the number of polymeric chains with a vinylidenic end group of polymeric chains (corresponding to the chain transfer process with the monomer) is closely in accordance with the data reported in Fig. 33. 

The main processes observed and reported are formation of vinylidene double bonds and abstraction of methyl groups. The concentration of unsaturations located mainly at the end of a polymer chain produced during radiolysis was found to be increasing with dose. Moreover, a linear relationship between unsaturations and scissions formed was noted over the temperature range of 83 to 363 K (-310 to 194°F). The ratio of double bonds to scissions was found to be independent of temperature and dose. - ... 

The main processes observed and reported were formation of vinylidene double bonds176477482 and abstraction of methyl groups. The concentration of unsaturations located mainly at the end of a polymer chain produced during radiolysis was found... 

In our experiments the monomer concentration was between about 150 and 200 grams per kg. of emulsion. Sodium dodecyl sulfate in a concentration of 5 to 15 grams per kg. of water was used as an emulsifier. The reaction temperature was generally 25 °C. Only with vinylidene chloride and chloroprene a reaction temperature of 5°C. was used because of the low boiling point of these monomers. Dose rate ranged between about 500 and 2000 rads per hour but was kept constant during each experiment. 

Vinylidene chloride and chloroprene (Figures 7 and 8) under the given conditions produce curves which more or less resemble the styrene curve. Vinylidene chloride especially shows a long period of a rather constant reaction rate. By the theory of Harkins and Smith-Ewart this would be interpreted as a period of constant particle number and of constant monomer concentration at the reaction site—i.e., the monomer-polymer particles. The first assumption seems justified (15). The second assumption of constant monomer concentration at the reaction site can be true only in a modified sense because poly (vinylidene chloride) is insoluble in its monomer, and the monomer-polymer particles in this system therefore have a completely different structure as compared with the monomer-polymer particles in the styrene system. 

Vinylidene chloride is a central ncr ous system depressant. Repeated exposure to low concentrations of vinylidene chloride may cause liver and renal dysfunction (Torkelson Rowe, 1981). Skin contact with vinylidene chloride causes irritation, which may be due partly to the presence of an inhibitor, hydroquinone monomethyl ether (Chivers, 1972). In one study, spirometry, blood clinical chemistry for liver and renal toxicity, haematological parameters and blood pressure measurements did not differ between vinylidene chloride-exposed workers and controls. Measured past time-weighted average vinylidene chloride concentrations ranged from < 5 to 70 ppm [< 20-280 mg/m- ] (Ott et al., 1976). 

Forkert, 1992). Administration of 125 mg/kg bw vinylidene chloride to male CD-I mice by intraperitoneal injection caused a decrease in GSH levels in lung within 6 h after exposure (Forkert Moussa, 1993). However, GSH concentrations returned to normal levels by 24 h. 

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