CHAIN TRANSFER TO MONOMER IN THE FREE-RADICAL POLYMERIZATIONS OF METHYL-METHACRYLATE, STYRENE, AND ALPHA-METHYLSTYRENE

The monomer chain transfer constant (C-M) has been evaluated for three monomers in bulk polymerization, viz, methyl methacrylate (MMA), styr ene (STY) and alpha-methyl styrene (AMS). The new chain length distrib ution (CLD) analytical method was utilized to determine values for C-M at the low initiation limit and compared to the traditional Mayo meth od. The values for C-M obtained at 50 degrees C using the CLD method w ere (C-M X 10(5)) 5.15, 5.27, and 412 for MMA, STY, and AMS, respectiv ely. The extremely high value for AMS originates in the low propagatio n rate coefficient for AMS. The values for the chain transfer rate coe fficients (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 s imilarity of the values for k(tr) are discussed in terms of possible m echanisms for the chain transfer to monomer reaction. The strong influ ence of transfer to monomer as a chain-stopping mechanism in AMS polym erization was confirmed by end group studies using matrix-assisted las er desorption ionization mass spectrometry.