Living Polymerizations of Polar and Nonpolar Monomers by the Catalysis of Organo Rare Earth Metal Complexes

Abstract

Abstract This review article deals with the rare earth metal initiated polymerization of polar and nonpolar monomers in living fashion (“living” means very active without termination and chain transfer reaction) to give monodisperse high molecular weight polymers at high conversion. A typical example is seen in the polymerization of methyl methacrylate with [SmH(C5Me5)2]2 or [LnMe(C5Me5)2(THF)] (Ln = Sm, Y, and Lu), giving high molecular weight syndiotactic polymers (Mn > 500000, syndiotacticity > 95%) quantitatively at low temperature (−95 °C). The initiation mechanism was discussed on the basis of X-ray analysis of the 1 : 2 adduct (molar ratio) of [SmH(C5Me5)2]2 with MMA. Living polymerizations of alkyl acrylates (methyl acrylate, ethyl acrylate, and butyl acrylate) were also possible by the catalysis of [LnMe(C5Me5)2(THF)] (Ln = Sm, Y); i.e. poly(methyl acrylate) Mn = 48 × 103, Mw/Mn = 1.04, poly(ethyl acrylate) Mn = 55 × 103, Mw/Mn = 1.04, and poly(butyl acrylate) Mn = 70 × 103, Mw/Mn = 1.05. By taking advantages of the living polymerization ability, we attempted ABA triblock copolymerization of MMA/butyl acrylate/MMA to obtain rubber-like elastic polymers. Lanthanum alkoxide(III) has good catalytic activity for the polymerization of alkyl isocyanates (Mn > 106, Mw/Mn = 2.08). Monodisperse polymerizations of lactones, lactide, and various oxiranes were also achieved by polymerization with rare earth metal complexes. C1 symmetric bulky organolanthanide(III) complexes such as {SiMe2[2(3),4-(SiMe)2C5H2]2LnCH(SiMe3)2} (Ln = La, Sm, and Y) show high 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 activity for the polymerization of ethylene. Thus, polyethylene of Mn > 106 (Mw/Mn = 1.6) was first obtained by using {SiMe2[2(3),4-(SiMe3)2C5H2]2Sm(THF)}. 1,4-Cis conjugated diene polymerization of 1,3-butadiene and isoprene became available by the efficient catalytic activity of NdCl(C5H5)2/AlR3 or Nd(octanoate)3/AlR3. The Ln(naphthenate)3/AliBu3 system allows selective polymerization of acetylene in cis-fashion. Utilyzing the fact that rare earth metal initiated living polymerization proceeds for both polar and nonpolar monomers, researchers have attempted to block copolymerization of ethylene with MMA or lactones yielding polyethylene derivatives having high chemical reactivity.