Free‐radical polymerization of methyl methacrylate initiated by thiol alone

Three different alkyl thiols, i.e., n ‐propylthiol, isopropylthiol, and 2‐methyl‐2‐undecanethio1, were proved efficient to initiate the polymerization of methyl methacrylate at 40°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.