Fundamental Studies and Recent Advances in Anionic Polymerization: 2. Living Polymerization

This paper reviews a general aspect of living polymerization. A living polymerization proceeds only in initiation step, followed by propagation step, but in the absence of the kinetic steps of termination and/or chain transfer. The propagating chain-end active center remains its activity after the completion of the polymerization. It is therefore possible to control the molecular weight by adjusting the feed ratio of monomer to initiator. The molecular weight distribution becomes narrow when the initiation is faster than the propagation in rate. The index value, Mw/Mn, reaches to near 1 according to the equation, Mw/Mn=1+1/DP (DP: Number average degree of polymerization). Using the living polymerization methodology, a variety of macromolecules with complex architectures is precisely synthesized. These polymers involve block and graft copolymers, chain-end-functionalized polymers, cyclic polymers, comb-like polymers, regular and asymmetric star-branched polymers, and various hyperbranched polymers with well-defined structures. Recently developed other mechanistic types of living polymerizations are also described including group transfer, cationic, radical, transition metal and rare earth metal-catalyzed, and ring-opening metathesis polymerizations.