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(C5Me5)2]2 or LnMe(C5Me5)2(THF) (Ln=Sm,Y, Lu etc.), giving high molecular weight syndiotactic polymers (Mn>1000,000, syndiotacticity >95%) quantitatively at low temperature (−95 °C). Synthesis of high molecular weight isotactic poly(MMA) with very low polydispercity was for the first time achieved by the efficient catalytic action of [(SiMe3)3C]2Yb. Living polymerizations of alkyl acrylates were also possible by the excellent catalysis of LnMe(C5Me5)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(C5R5)2 or LnR(C5R5)2 conducted the living polymerizations of various lactones such as β-propiolactone, δ-valerolactone and ε-caprolactone, and also conducted the block copolymerizations of MMA with various lactones. C1-symmetric silylene bridged bulky organolanthanide(III) complexes such as SiMe2[2(3),4-(SiMe3)2C5H2]2LnCH(SiMe3)2 (Ln=La, Sm, Y) show high catalytic activity for linear polymerization of ethylene. Organolanthanide(II) complexes such as racemic SiMe2[2-SiMe3-4-tBu-C5H2]2Sm(THF) as well as C1-symmetric SiMe2[2(3),4-(SiMe3)2C5H2]2Sm(THF) were also found to have high catalytic activity for the polymerization of ethylene, giving Mn>106 with Mw/Mn=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.