Chain transfer constants (C(tr)) for thiuram disulfide (TD) groups, included in the backbone of polydimethylsiloxane (PDMS) of different chain lengths, in methyl methacrylate (MMA) and styrene (St) were determined from measurements of the degree of polymerization. Two methods were used. The first consisted of using the initiation and transfer properties of the thiuram disulfides groups, and the second, of using a more efficient free radical initiator than TD groups, in which case the former behaves only as a transfer agent. In both the methods, the C(tr) of TD was evaluated in bulk polymerization of MMA at 60, 70, 80, and 90-degrees-C. Using the first method, the C(tr) of TD was measured also in solution polymerization of MMA in toluene at 100-degrees-C and, with the second one, in bulk polymerization of styrene at 60, 80, and 90-degrees-C. PDMS-based macrothiuram disulfide (macroiniferter) behaves as an "azeotropic" transfer agent for MMA and styrene at 125-degrees-C and 110-degrees-C, respectively.