Chain Transfer to Monomer in the Free-Radical Polymerizations of Methyl Methacrylate, Styrene, and α-Methylstyrene

Abstract

The monomer chain transfer constant (CM) has been evaluated for three monomers in bulk polymerization, viz, methyl methacrylate (MMA), styrene (STY) and α-methyl styrene (AMS). The new chain length distribution (CLD) analytical method was utilized to determine values for CM at the low initiation limit and compared to the traditional Mayo method. The values for CM obtained at 50 °C using the CLD method were (CM × 105) 5.15, 5.27, and 412 for MMA, STY, and AMS, respectively. The extremely high value for AMS originates in the low propagation rate coefficient for AMS. The values for the chain transfer rate coefficients (ktr) were calculated were (ktr × 102 dm3·mol-1·s-1), 3.34, 1.25, and 0.711 for MMA, STY, and AMS, respectively. The similarity of the values for ktr are discussed in terms of possible mechanisms for the chain transfer to monomer reaction. The strong influence of transfer to monomer as a chain-stopping mechanism in AMS polymerization was confirmed by end group studies using matrix-assisted lase...