This invention relates to a process for controlling the architecture of copolymers of at least two unsaturated monomers, made by free-radical polymerization in the presence of a cobalt-containing chain transfer agent, including the control of molecular weight, degree of branching and vinyl end group termination, by varying at least one of the variables of molar ratio of monomers, their relative chain transfer constants, polymerization temperature and degree of conversion and amount of cobalt chain transfer agent; and polymers made thereby.