A polymerization method including radically polymerizing a monomer in a polymerization medium comprising a chain transfer agent, and a free radical initiator prepared by oxidizing a reaction product of a ligand-reactive decomplexation agent and an alkyl-borane complex of the formula:




wherein R1, R2, and R3 are independently selected from hydrogen, an alkyl group containing from 1 to 12 carbon atoms, a cycloalkyl group containing from 3-12 carbon atoms, and an aryl group containing from 6 to 12 carbon atoms, wherein the aryl group may be optionally substituted with an alkyl group having from 1 to 10 carbon atoms, and at least one of R1, R2, and R3 is an alkyl group, a cycloalkyl group or an aryl group, and L is a complexing agent selected from one or more amine groups, amidine groups, hydroxide groups, alkoxyl groups, alkyl ether groups, alkoxide groups and mixtures thereof.