Effect of polyfunctional chain transfer agents on the molecular weight distribution in free-radical polymerization: Polymerization of methyl methacrylate in the presence of polyfunctional chain transfer agents

摘要

Polymerization of methyl methacrylate was carried out in the presence of polyfunctional chain transfer agents: 1,6-hexanedithiol, trimethylolpropane tris(mercaptoglycolate) and pentaerythritol tetrakis(3-mercaptopropionate). The theoretical results reported in the preceding papers are completely confirmed: the experimental values of the dispersion index (D = M_w/M_n) are 1.62 for f = 2, 1.39 for f = 3 and 1.28 for f = 4. In the case of bifunctional transfer agents the molecular weights calculated are in very good agreement with those obtained by size exclusion chromatography. The formation of star-shaped macromolecules was confirmed by cleavage of the C―S―C bonds. The number-average molecular weight decreases and the dispersion index is approximately equal to 2 after exposure to UV rays. The phenomenon of "pseudo-living" polymerization in the presence of polyfunctional chain transfer agents is also discussed.