Concentration styrene

The kinetics of initiation reactions of alkyllithium compounds often exhibit fractional kinetic order dependence on the total concentration of initiator as shown in Table 2. For example, the kinetics of the initiation reaction of //-butyUithium with styrene monomer in benzene exhibit a first-order dependence on styrene concentration and a one-sixth order dependence on //-butyUithium concentration as shown in equation 13, where is the rate constant for... 

Figure 8. Overall conversion vs. time, and polymer composition, styrene concentration in the particles, and MMA concentration in the particles vs. overall conversion for the data of Nomura and Fujita (12.). Initial weight ratio (MMA/Total monomer) = 0.5.

Temperature Concentration of TiCl4 mol/1 Isobutene concentration mol/1 % yield Styrene concentration mol/1 % yield % yield on addition of water... 

The pseudocationic polymerisations are tentatively explained in terms of an ester as the active species. For the styrene-perchloric acid system it is known that this ester is only stable in the presence of an at least four-fold excess of styrene. When, at the end of a polymerisation, the styrene concentration has fallen to this level, the ester ionises. When styrene is mixed with an excess of acid in dilute solution, protonation is the only reaction [5-7]. 

Pepper and Reilly s views on the mechanism of this polymerisation implied that with the concentrations of perchloric acid used by them, it should be possible to estimate the concentration of polystyryl ions spectrophotometrically and so to test whether initiation did indeed give carbonium ions in concentration equal to that of the acid. When Gandini and Plesch [5, 29-31] carried out the appropriate measurements, they found from spectroscopic, conductimetric and kinetic studies that no ions were present during the polymerisations, but that they were formed once the styrene concentration had been reduced by polymerisation to less than four times the concentration of acid. Addition of more styrene instantly removed the ions, which reappeared once again when polymerisation had reduced the styrene concentration sufficiently. This formation of ions after polymerisation had misled some workers into concluding that they were also present during that reaction. 

We report spectroscopic and conductimetric studies on the reactions of styrene in the presence of perchloric acid (most in methylene dichloride but some in ethylene dichloride), both during and after the polymerisation. During polymerisation no ions are detectable, but at the end aralkyl (and subsequently allylic) ions are formed. Quantitative results show that ion formation sets in when the styrene concentration has fallen to four times the acid concentration we interpret this finding as showing that the ester (oligo-)styryl perchlorate requires four molecules of styrene for stabilisation in solution. 

Table 2 Spectroscopic (SGU) and conductimetric (SGC) experiments at fixed initial styrene concentration in CH2CI2 at room temperature ...

The following discussion is based on our earlier conclusion that the propagating species in these polymerisations is oligostyryl perchlorate ester, which is stabilised in solution by excess styrene. One question arising concerns the number of molecules of styrene per ester molecule required for this stabilisation another concerns the kinetics and mechanism of the ionogenic reactions which ensue once the styrene concentration has been reduced by polymerisation to such a low level that the quantity of styrene no longer suffices to stabilise the ester. 

Another, necessarily much less precise, method for determining n is available from the kinetic experiments [1]. At the end of these reactions, at the precise instant at which the reaction mixtures turned yellow, a very fast reaction took place (Figure 5). This represents the polymerisation of the residual styrene by a true cationic reaction caused by the ions formed from the ester at the point where the styrene concentration was reduced to a level no longer sufficient to stabilise the ester. From the very small temperature rise during this final fast reaction, the number of styrene molecules polymerised could be calculated it was always about four times the initial concentration of perchloric acid. This phenomenon was particularly evident in the reactions carried out at -19 °C in which relatively high acid concentrations were used so as to obtain reasonably fast polymerisations [1]. 

Homopolymerisation which accompanies copolymerisation increases at higher styrene concentrations, thus the grafting efficiency decreases with increasing styrene concentration (Table V). These results are similar to analogous data for polypropylene (5, 6). Inclusion of mineral acid increases homopolymerisation, however not to the same degree as it enhances copolymerisation, thus, overall, grafting efficiency is significantly improved in the presence of acid. 

In the middle range of styrene concentrations, a compromise is attained where there is sufficient styrene to scavenge all excess methanol radicals not involved in activation of the trunk polymer, yet an excess of monomer remains for grafting by the charge-transfer mechanism proposed by Dilli and Garnett (12) originally for copolymerisation to cellulose (4) and subsequently extended to wool (3), polyolefin (2,5) and PVC (13) systems. The data in Table V are consistent with this interpretation. 

Further work (10) with acid effects in the radiolysis of binary mixtures such as benzene-methanol and pyridine-methanol indicates that the acid phenomenon is more complicated than the simple H atom model originally developed ( ). These more recent experiments (10) show that whilst increased hydrogen atom yields in the presence of acid enhance the overall grafting yield, other mechanisms also contribute to this acid effect. Thus the acid stability of intermediate radicals (I-III) and also analogous species involving the trunk polymer are important. With radicals (I-III), at low styrene concentrations in methanol, these intermediates (MR-) will predominantly react with other available... 

Pygas is fractionated to make a Cs heart cut, a stream with the styrene concentrated in it. This is usually done before the pygas is hydrotreated in preparation for using it as a gasoline blending component. Otherwise the styrene would hydrogenate as well. 

The styrene concentrate is fed to a solvent recovery process or an extractive distillation process. The solvent selectively pulls the styrene out of the hydrocarbon mixture. The styrene raffinate, sans styrene, is sent back to be mixed with the pygas (although it can also be fractionated to pull out a high quality mixed xylene.)... 

De Visscher et al. (1996) investigated the sonolysis of styrene and other monocyclic aromatic compounds in aqueous solution by 520 kHz ultrasonic waves. The experiments were performed in a 200-mL glass reactor equipped with a cooling Jacket maintained at 25 °C. At initial styrene concentrations and sonication times of 0.25 mM and 40 min, 0.49 mM and 80 min, and 0.97 mM and 80 min, the first-order reaction rates were 0.03292, 0.02409, and 0.01262/min, respectively. 

Source Based on laboratory analysis of 7 coal tar samples, styrene concentrations ranged from ND to 2,500 ppm (EPRI, 1990). A high-temperature coal tar contained styrene at an average concentration of 0.02 wt % (McNeil, 1983). 

Fig. 3-3 Effect of styrene concentration on the initiator efficiency of azobisisobutyronitrile. . o and refer to experiments with initiator concentrations of 0.20, 0.50, and 1.00 g I, 1, respectively. After Bevington [1955] (by permission of Faraday Society, and Royal Society of Chemistry, London).

Copolymerization of methyl methacrylate with styrene in the presence of isotactic poly(methyl methacrylate) has been examined by O Driscoll and Capek. Copolymerization was carried out in acetone at O C and redox system benzoyl peroxide -dimethylaniline was used to initiate the polymerization process. Carrying out the process with various ratios of styrene to methyl methacrylate, it was found that the polymerization rate drops very quickly with the increase in styrene concentration. A very small amount of styrene destroys any template effect that it-poly(methyl methacrylate) exerts on the rate of the polymerization. Assuming, that the reactivity ratios are not changed by the template (ri = i2 = 0.5), the critical length of the sequence of methacrylic units is 10- 20. Complexation occurs only if longer sequences, composed of methacrylic... 

Previously (7) we published a curve which was obtained at intermediate SDS concentration with a somewhat lower styrene concentration and roughly one-tenth of the dose rate. This curve showed a rather good classic form. 

At the mass-transfer limited current density (i/i = 1) always the dimer yield vanishes and it approaches its respective highest value, which depends—but not linearly—on the styrene concentration at vanishing current densities. This result can be formalized by assuming the coupling reaction [Eq. (42b)] and the solvolysis [Eq. (42c)] of the primary radical cation as a heterogeneous reaction of adsorbed reactants. Under this condition, one obtains the expression for the dimer yield,... 

Polystyrene is preferentially formed on the cathode surface. MMA cannot be incorporated until the styrene concentration at the electrode is reduced substantially during the course of the reaction. 

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