Trityl hexachloroantimonate

Table 5-1 shows the various kinetic parameters, including k+ and kp, in the polymerization of styrene initiated by triflic acid in 1,2-dichloroethane at 20°C. Data for the polymerization of isobutyl vinyl ether initiated by trityl hexachloroantimonate in methylene chloride at 0°C are shown in Table 5-2. Table 5-3 shows values for several polymerizations initiated... 

At low temperatures in inert solvents (such as methylene dichloride) a controlled polymerization can be effected using various acids and alkylating agents. These initiators include boron trifluoride etherate, triethylaluminum, trityl hexachloroantimonate, triethylam-monium hexachloroantimonate, diethyloxonium hexafluoroantimonate, p-toluenesulfonic acid and diethylzinc or cadmium-1,2-dioI complexes. Crystalline, high molecular weight... 

Trityl hexachloroantimonate polymerizes styrene only at relatively high concentrations (>10-2 M) [145]. This is apparently due to rapid formation of the covalent chloro adducts, which are relatively inactive in the presence of only a small amount of Lewis acid. Moreover, the SbCls generated in this reaction can add to styrene to form a 1,2-dichloroadduct and inactive SbCI3. In contrast, polymerization is fast with trityl hexaflu-oroantimonate [145], demonstrating the SbF6 counterion does not decompose to SbFs and F-terminated chains. 

Trityl hexachloroantimonate-initiating systems behave similarly [145]. In contrast, only a small concentration of BCI3 is required to complete BCU-initiated polymerizations in the absence of water because haloboration (Section III.A.3.a.2) is usually slow. 

Another method for enhancing the efficiency of initiation is to deactivate for growing species to a larger degree than the initiator. The use of sulfides as deactivators in the polymerization of vinyl ethers initiated by triflic acid and by trityl hexachloroantimonate are examples [37,38,135]. 

The study of the polymerisation of cyclopentadiene by stable carbenium salts has been the exclusive domain of S walt and his group. In 1967, they reported the first observations on a system involving trityl hexachloroantimonate in methylene chloride between — 70 and 20°C Because of the interesting features of this polymerisation, the work was pursued by kinetic and mechanistic investigations. In I969 it was shown that initiation took place by direct addition and that transfer and termination were imimpor-tant particularly in the first stipes of the process. The kinetics of initiation were followed by visible spectroscopy and provided furthw evidence for a one-to-one reaction. Thus,... 

Within the context of their invest ation Vairon and Villesai e observed that the interaction of cyclopentadiene with trityl hexachloroantimonate in carbon tetrachloride or benzene produced the rapid disappearance of the characteristic yellow colour of the trityl ion but no polymerisation. This interesting phenomenon of false initiation has also been reported in some systems involving styrene and will be disaissed when we deal with this monomer. 

Recent unpublished work by Sauvet has shown that trityl hexachloroantimonate can induce the dimerisation of 1,1-diphenylethylene. However, this process requires high concentrations of initiator probably because the interaction of the trityl ion with the monomer is sterically hindered. Most of the dimerisation proceeds by proton transfer once initiation has taken place. It is therefore difficult to look for evidence on the chemistry of the initial step since most of the product is the linear unsaturated dimer. 

With one molar equivalent of trityl hexachloroantimonate, compound 116 is converted to a monocation 117 in 88% yield. The latter is transformed by triethylamine in almost quantitative yield into the quinonoid compound 118. The relationship between this system and the dibenzotetrathiafulvalene is expected to be similar to that between tetracyanoethylene and TCNQ, and the donor properties of 118 were demonstrated by charge-transfer complex formation. ... 

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