([bis[mu-[(2,3-butanedione dioximato)(2-)-O:O']] tetrafluorodiborato(2-)-N, N' ,N ",N'''] cobalt), CoBF, has been used for the effective catalytic chain transfer of alkyl methacrylate homo- and copolymers under emulsion polymerization conditions. The catalytic chain transfer process reduces the rate of polymerization such that when the monomer is fed over 60 min the instantaneous conversion is low enough for the particle to be swollen with monomer, allowing diffusion of the catalysts between the aqueous and monomer phases. When the amount of the catalyst is reduced, the rate is increased, eventually leading to viscous, glassy particles that prevent catalyst mobility, which is observed as a breakdown in the polymerization mechanism. This can be circumvented by the addition of a 20% shot of monomer at the start of the reaction. The effective chain transfer coefficient decreases on increasing the length of the ester group of the methacrylate. The analysis of the polymers made by the technique described shows that the T-g of the polymers observe a broad transition due to the effect of chain length being pronounced at low molecular mass.