FREE-RADICAL POLYMERIZATION OF METHYL-METHACRYLATE INITIATED BY THIOL ALONE

Three different alkyl thiols, i.e., n-propylthiol, isopropylthiol, and 2-methyl-2-undecanethiol, were proved efficient to initiate the polymerization of methyl methacrylate at 40-degrees-C. The initial polymerization rate, R(p), increases with increasing thiol concentration but cannot be described by a single-power law. However, R(p) is proportional to 1.3th power of the monomer concentration, indicating the participation of monomer in the initiation reaction. With increase of the polarity of solvents, R(p) decreases, demonstrating the polar property of the initiating intermediate. The apparent activation energy of overall polymerization was calculated to be 9.3 kcal/mol. Molecular weight measurements indicated the twofold function of the thiol as both an initiator and a regulator.