Chain transfer to monomer in the free-radical polymerizations of methyl methacrylate, styrene, and α-methylstyrene

The monomer chain transfer constant (C-M) has been evaluated for three monomers in bulk polymerization, viz, methyl methacrylate (MMA), styrene (STY) and alpha-methyl styrene (AMS). The new chain length distribution (CLD) analytical method was utilized to determine values for C-M at the low initiation limit and compared to the traditional Mayo method. The values for C-M obtained at 50 degrees C using the CLD method were (C-M X 10(5)) 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 (k(tr)) were calculated were (k(tr) x 10(2) dm(3).mol(-1).s(-1)), 3.34, 1.25, and 0.711 for MMA, STY, and AMS, respectively. The similarity of the values for k(tr) 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 laser desorption ionization mass spectrometry.