Organo-rare-earth-metal initiated living polymerizations of polar and nonpolar monomers

This review article deals with the rare-earth-metal initiated living polymerizations of polar and nonpolar monomers to give monodisperse high molecular weight polymers at high conversion. A typical example is seen in the polymerization of methyl methacrylate (MMA) with [SmH(C(5)Me(5))(2)](2) or LnMe(C(5)Me(5))(2)(THF) (Ln = Sm,Y, Lu etc.), giving high molecular weight syndiotactic polymers (M(n) > 1000,000, syndiotacticity > 95 %) quantitatively at low temperature; ( -95 degreesC). Synthesis of high molecular weight isotactic poly(MMA) with very low polydispercity was for the first time achieved by the efficient catalytic action of [(SiMe(3))(3)C](2)Yb. Living polymerizations of alkyl acrylates were also possible by the excellent catalysis of LnMe(C(5)Me(5))(2)(THF) (Ln = Sm, Y). By taking advantages of the living polymerization ability, we attempted the ABA-type triblock copolymerization of MMA-butyl acrylate-MMA to obtain rubber-like elastic polymers. Organo-rare-earth-metal complexes such as LnOR(C(5)R(5))(2) or LnR(C(5)R(5))(2) conducted the living polymerizations of various lactones such as beta-propiolactone, delta-valerolactone and epsilon-caprolactone, and also conducted the block copolymerizations of MMA with various lactones. C(1)-symmetric silylene bridged bulky organolanthanide(III) complexes such as SiMe(2)[2(3),4-(SiMe(3))(2)C(5)H(2)](2)LnCH(SiMe(3))(2) (Ln = La, Sm, Y) show high catalytic activity for linear polymerization of ethylene. Organolanthanide(II) complexes such as racemic SiMe(2)[2-SiMe(3)-4-tBu-C(5)H(2)](2)Sm(THF) as well as C(1)-symmetric SiMe(2)[2(3),4-(SiMe(3))(2)C(5)H(2)](2)Sm(THF) were also found to have high catalytic activity for the polymerization of ethylene, giving M(n) > 10(6) with M(w)/M(n) = 1.6. Utilizing the high polymerization activity of rare-earth-metal complexes towards both polar and nonpolar monomers, block copolymerizations of olefins with polar monomers such as MMA and lactones were for the first time realized. (C) 2002 Elsevier Science B.V. All rights reserved.