Conversion styrene

One of the key benefits of anionic PS is that it contains much lower levels of residual styrene monomer than free-radical PS (167). This is because free-radical polymerization processes only operate at 60—80% styrene conversion, whereas anionic processes operate at >99% styrene conversion. Removal of unreacted styrene monomer from free-radical PS is accompHshed using continuous devolatilization at high temperature (220—260°C) and vacuum. This process leaves about 200—800 ppm of styrene monomer in the product. Taking the styrene to a lower level requires special devolatilization procedures such as steam stripping (168). 

Interestingly, the specific environment of the ionic solvent system appears to activate the chiral Ni-catalyst beyond a simple anion-exchange reaction. This becomes obvious from the fact that even the addition of a 100-fold excess of Fi[(CF3S02)2N] or Na[BF4] in pure, compressed CO2 produced an at best moderate activation of Wilke s complex in comparison to the reaction in ionic liquids with the corresponding counter-ion (e.g., 24.4 % styrene conversion with 100-fold excess of Fi[(CF3S02)2N], in comparison to 69.9 % conversion in [EMIM][(CF3S02)2N] under otherwise identical conditions). 

Continuous Polymerizations As previously mentioned, fifteen continuous polymerizations in the tubular reactor were performed at different flow rates (i.e. (Nj g) ) with twelve runs using identical formulations and three runs having different emulsifier and initiator concentrations. A summary of the experimental runs is presented in Table IV and the styrene conversion vs reaction time data are presented graphically in Figures 7 to 9. It is important to note that the measurements of pressure and temperature profiles, flow rate and the latex properties indicated that steady state operation was reached after a period corresponding to twice the residence time in the tubular reactor. This agrees with Ghosh s results ). 

The styrene conversion versus reaction time results for runs in the laminar flow regime are plotted in Figure 8. Both the rate of polymerization and the styrene conversion increase with increasing flow rate as noted previously (7). The conversion profile for the batch experimental run (B-3) is presented as a dashed line for comparison. It can be seen that the polymerization rates for runs with (Nj e e 2850 are greater than the corresponding batch polymerization with a conversion plateau being reached after about thirty minutes of reaction. This behavior is similar to the results obtained in a closed loop tubular reactor (7J) and is probably due to an excessively rapid consumption of initiator in a... 

The styrene conversion for the continuous flow stirred tank experiments was determined utilizing the concentration of the polymer in the feed and the number average degrees of polymerization... 

Styrene conversion calculated by this equation and styrene conversion obtained for runs 12-15 by gravimetric methods were in good agreement. In general, the gravimetric technique was 1 to 5% points greater than conversions calculated using the GPC data. 

The nature of the chlorinated reagent is crucial for promoting the Kharasch addition reaction (Equation 8.11). The results showed that carbon tetrachloride could be added to various olefins in a regioselective way. Under these reaction conditions, no polymerization products were detected. In contrast, when chloroform was used as the halide source the methyl methacrylate and styrene conversions reached only 33% and 40% with the best performing system (VIII), and a significant fraction of polymers was observed [61]. 

Influence of reaction temperature on styrene conversion over (Co,La)salen/MCM-41... 

Addition of pyridine bases to the catalytic system caused a considerable increase in the rate and selectivity of the reaction, reaching 80% yield of styrene oxide for 100% styrene conversion (r.t., 30 min). In the presence of this pyridine-modified system, the reactivity of alkenes is in the order styrene > trisubstituted > cis-disubstituted > trans-disubstituted> monosubstituted. The epoxidation of alkenes is not stereoselective. In the absence of pyridine, cis-stilbene was converted into a 1.8 1 trans cis epoxide mixture, whereas the cis isomer prevails in the presence of excess pyridine ligands. Neither chlorohydrins nor pyridine N-oxides are involved in this catalytic system. Attempts to isolate the reactive intermediate led to the characterization of a relatively stable... 

Figure 5.13 Styrene conversion vs polyester C=C conversion for different molar ratios (MR) of styrene to polyester C=C double bonds, followed by FTIR. (Reprinted from Yang and Lee, 1988, Copyright 2001, with permission from Elsevier Science)...

Titanium compound [Al(Me)0] unit/Ti molar ratio Styrene conversion (%) Reference... 

The Sheldon group found that the highest conversions were observed with CrS-1 prepared by the ammonia method. CrS-1 made by the fluoride method gave a slightly lower styrene conversion and roughly the same selectivities. The catalyst prepared by the sulfuric acid method gave substantially lower styrene conversions, but the selectivity to benzaldehyde was high. 

Figure 27 Oxidative dehydrogenation paths that can be employed to facilitate ethylbenzene to styrene conversion.

Polymerizations of styrene containing 50 ppm of SEM were conducted using the same conditions employed in the control experiments. The results (Table 4.2) indicate that the presence of SEM results in lower styrene conversions, making it impossible to make a good comparison of the effect (relative to the control) of the acid during subsequent high-temperature treatment. However, the data indicate that SEM does not act as a catalyst to reduce significantly the level of residual styrene in the polymer. 

Figure 7.8 Effect of acid strength on styrene conversion (140 °C/2 h) [14]. Reprinted from W. C. Buzanowski, J. D. Graham, D. B. Priddy and E. Shero, Polymer, 33, 3055(1992) with permission of Elsevier Science...

In a more conventional example Pt/ZSM-5 is used to induce reactant (size exclusion) selectivity in the hydrogenation of substituted aromatic molecules. Over Pt/ZSM-5 the rate of styrene conversion is at least 25 times higher than that of methylstyrene, while over Pt/Al Oj similar rates of hydrogenation were observed for both these compounds. 

Figure 11 Selectivity in hydrogenation of styrene/l-octene mixtures a test case octenes versus styrene conversion (aromatics hydrogenation always much less than 0.2%). (From Ref. 33.)...

The activity of the [( -2-MeC3H4)Pd(cod)] BF4 -2PR3 catalysts (based upon styrene conversion) is found to increase in the order [20] ... 

Fig. 7. Variation of styrene conversion with time in membrane reactor...

The experimental data on the Pn of homopolystyrene, the efficiency of polystyrene grafting to rubber, and the dependence of styrene polymerization on rubber concentration were compared with the calculated data, with up to 8% of styrene conversion at T = 100 °C. 

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