1966 Volume 39 Issue 10 Pages 2206-2211
In order to study the effects of aromatic sulfur derivatives on radical polymerizations, dibenzoyl disulfide (DBDS) and its derivatives were prepared and used as initiators or chain transfer agents for the polymerizations of styrene and methyl methacrylate. All of these derivatives failed to act as initiators of thermal polymerizations, but they did prove effective photosensitizers. The rates of polymerizations were found not to be proportional to the square-root concentration of the initiator (DBDS) used. The sulfur radical derived from the photo-dissociation of DBDS affected not only the initiation reaction, but also the termination reaction. The chain transfer constants to DBDS derivatives in the polymerization of styrene and methyl methacrylate showed no linear relationship with Hammett’s equation (logC⁄C0=ρσ), but a linear relationship was obtained when a modification of Hammett’s equation (logC⁄C0=ρσ+γER) was applied. From the plot obtained by the use of logC⁄C0=ρσ+γER, the γ value, which indicates the extent of resonance stabilization in the transition state was found to be 6.0 upon the polymerization of styrene at 60°C. Under similar conditions, however, the γ-value for benzoyl peroxide was calculated as 3.0 from the results of Cooper. This difference may be explained from an increased 3d-orbital resonance stabilization of DBDS in the transition state.
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