Like the chain transfer constant of carbon tetrachloride also the chain transfer constants of methylene bromide, bromoform, and bromotrichloromethane depend on monomer concentration in the polymerization of styrene. Whereas the chain transfer constant,$$bar C$$, of carbon tetrachloride decreases with decreasing monomer concentration, the reverse holds for methylene bromide and bromoform. Only for bromotrichloromethane a small increase of$$bar C$$is observed with increasing styrene concentration. If it is again assumed that in presence of styrene the chain transfer agents named above exist in two forms of different reactivity-one free and one as a complex with monomer-contrary to what has been observed with carbon tetrachloride, the complexed forms of methylene bromide and bromoform must be the less reactive chain transfer agents compared to the free forms. Only in the case of bromotrichloromethane the complex has the higher reactivity in chain transfer. Further support for these views is gained from experiments carried out in presence of durene, which is a stronger complexing agent than styrene.
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