Copolymerizations of styrene (STY) and alpha-methylstyrene (AMS) have been performed at different monomer feed compositions and temperatures (40-70 degrees C) in the presence of the catalytic chain transfer agent bis(boron difluorodimethylglyoximate)cobaltate(II) (COBF). The average chain transfer constant, [C-s], was found to increase approximately 3 orders of magnitude upon going from pure Sm to pure AMS. The addition of only 10% AMS increased the (Cs) by 1 order of magnitude. This behavior can be predicted from the relative fractions of growing radical end groups, which results in the majority of polymer chains being formed with an unsaturated AMS end group. No significant penultimate unit effects in the chain transfer reaction were observed. The addition of 10-20% AMS results in the majority of the growing radicals having AMS end groups, and hence AMS dominates the catalytic chain transfer reaction. The [C-s] values continue to increase as the AMS content is increased beyond 20%; however, this can be mostly attributed to a decrease in [k(p)] rather than an increase in [k(tr)]. The expected end groups in the homopolymerization of AMS in the presence of COBF were confirmed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS).