EFFECT OF POLYFUNCTIONAL CHAIN TRANSFER AGENTS ON THE MOLECULAR-WEIGHT DISTRIBUTION IN FREE-RADICAL POLYMERIZATION .3. POLYMERIZATION OF METHYL-METHACRYLATE IN THE PRESENCE OF POLYFUNCTIONAL CHAIN TRANSFER AGENTS

Polymerization of methyl methacrylate was carried out in the presence of polyfunctional chain transfer agents: 1,6-hexanedithiol, trimethylolpropane (b)) 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 = ($) over bar M(w)/($) over bar 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.