Functionalization of poly(methyl methacrylate) by free radical polymerization, 1. Transfer with functional thiols

Chain transfer constants (Ctr) for three phosphonated thiols in methyl methacrylate (MMA) polymerization at 60°C were determined from measurements of the degree of polymerization. These thiols were: diethyl 2‐mercaptoethyl phosphate (1), diethyl 2‐mercaptoethylamidophosphate (2), and tetraethyl mercaptomethylethylene bis(phosphate) (3). Transfer efficiencies of the thiols were found to be dependent upon their structures. The Ctr value of thiol 2 with MMA was the lowest in the present series, which can be attributed to a possible charged tautomeric form which eventually may reduce the electron density on the thiol, thus rendering the chain transfer reaction with the PMMA radical less feasible. Ctr values of thiol 1 were evaluated at 55, 60, 65, 70 and 75°C. This thiol behaves as an “azeotropic” transfer agent for MMA at 96°C.