The present invention relates to a polymerization process for the control of the microstructure of polymers and to novel copolymers. An embodiment of the present invention relates a process of polymerizing first and second monomers in the presence of a complex comprising at least one of the monomers. The presence of the complex modifies the relative reactivity, or cross propagation rate constants, of the monomers in copolymerization reactions. Embodiments of the present invention allow the synthesis of polymers with novel stereochemistry and monomer sequence distribution, for example, but not limited to, copolymers with at least one segment of alternating monomers, a controlled molecular weight and narrow molecular weight distribution, or a segment of high concentration of the first monomer.