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

Abstract

This article deals with the rare earth metal initiated polymerization of polar and nonpolar monomers in a living fashion. For example, [SmH(C 5 Me 5) 2 ] 2 or LnMe(C 5 Me 5) 2 (THF) (Ln= Sm, Y and Lu) conducted the polymerization of methyl methacrylate(MMA) to give high molecular weight syndiotactic polymers (M n >500,000, 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 of [SmH(C 5 Me 5) 2 ] 2 with MMA. Synthesis of high molecular weight isotactic poly(MMA) with very narrow molecular weight distribution was for the first time realized by the efficient catalytic function of Yb[C(SiMe 3) 3 ] 2. Living polymeriza-tions of alkyl acrylates (methyl acrylate, ethyl acrylate, and butyl acrylate) 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 ABA 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 β-propiolactone, δ-valerolactone and ε-caprolactone, and also conducted the block copolymerizations of MMA with various lactones. Lanthanum alkox-ide(III) has good catalytic activity for the polymerization of alkyl isocyanates. Monodis-perse polymerizations of lactide and various oxiranes were also achieved by the use of rare earth metal complexes. C 1 symmetric bulky organolanthanide(III) complexes such as SiMe 2 [2(3),4-(SiMe) 2 C 5 H 2 ] 2 LnCH(SiMe 3) 2 (Ln=La, Sm, and Y) show high catalytic activity towards linear polymerization of ethylene. Organolanthanide(II) complexes such as ra-cemic SiMe 2 (2-SiMe 3-4-t Bu-C 5 H 2) 2 Sm(THF) 2 as well as C 1 symmetric SiMe 2 [2(3),4-(SiMe 3) 2 C 5 H 2 ] 2 Sm(THF) 2 were found to have high activity for the polymerization of ethyl-ene to give 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 copolymeriza-tions of ethylene with polar monomers such as methyl methacrylate and lactones were for the first time realized. 1,4-cis-Conjugated diene polymerization of 1,3-butadiene and iso-prene became available by the efficient catalytic activity of NdCl(C 5 H 5) 2 /AlR 3 or Nd(oc-tanoate) 3 /AlR 3. The Ln(naphthenate) 3 /AliBu 3 system allows selective polymerization of acetylene in cis-fashion.