Thiourea as a transfer agent in the radical polymerization of methyl methacrylate in aqueous solution at 42 |
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Authors: | D Pramanick AK Chatterjee |
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Institution: | Department of Chemistry, University of Kalyani, Kalyani, Nadia, West Bengal, India |
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Abstract: | Chain transfer involving thiourea in radical polymerization of methyl methacrylate in acidic aqueous media has been studied by polymer endgroup analysis using the dye-partition technique. Thiourea has feeble reactivity in chain transfer, the transfer constant with respect to poly (methyl methacrylate) radicals being 1.21 × 10?4 at 42°. This chain transfer study led to the development of a new method for studying the tautomeric equilibrium between the thione and thiol forms of thiourea. The equilibrium is pH dependent and the equilibrium constant at 42° is 232. The ratios of the equilibrium concentrations of the thiol to thione forms of thiourea at various pH's have been calculated. The thiol form is responsible for the chain transfer reactivity; it predominates in strongly acidic media and is almost absent above pH 3.5. This new method may be used for studying the thione-thiol tautomerism of other thiourea derivates. |
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