Seiji Tone

New approach to block copolymerization of ethylene with polar monomers by the unique catalytic function of organolanthanide complexes

This paper describes the first examples of ABA- and AB-type block copolymerizations of a nonpolar monomer, in this case ethylene, with polar monomers, such as methyl methacrylate (MMA), ϵ-caprolactone (CL), and 2,2-dimethyltrimethylene carbonate (DTC), initiated by the unique catalytic function of rare earth metal complexes [Sm(II) and Ln(III) (Ln = Y, Sm)] as initiators. The Sm(II) species conducts the ABA-type triblock copolymerization, leading to poly(MMA-co-ethylene-co-MMA), poly(CL-co-ethylene-co-CL), or poly(DTC-co-ethylene-co-DTC) by the efficient catalysis of racemic Me2Si(C5H2-2-Me3Si-4-tBu)2Sm(THF)2 (1) or meso Me2Si(Me2SiOSiMe2)(C5H2-3-tBu)Sm(THF) (2b). The resulting block copolymers are completely insoluble in THF and CHCl3, but the homopolymers of MMA, CL, and DTC are freely soluble in these solvents. TEM profiles provide direct evidence for the block copolymerizations, where the spheric morphology of homogeneously dispersed polar polymers was observed. Ln(III) species, such as racemic Me2Si(C5H2-2-Me3Si-4-tBuMe2Si)YH (5) and Me2Si(C5H2-2-Me3Si-4-tBu)SmH (6), afford AB-type block copolymers between ethylene and MMA or CL, whose TEM images reveal the homogeneous dispersion of poly(MMA) or poly(CL) units in the polyethylene region. The ABA- and AB-type block copolymers demonstrate high break stress and high tensile modulus as compared with their corresponding blended polymers.

Chain transfer polymerization of methyl methacrylate initiated by organolanthanide complexes

A novel chain transfer polymerization mediated by Cp 2 *Sm(III) species and organic acids is described. The chain transfer polymerization involves the reaction of organic acids such as thiols or ketones with an active bond between samarium(III) and the enolate in a living chain and of poly(methyl methacrylate) (PMMA). This chain transfer reaction resulted in termination of the living chain end and the regeneration of the active initiator which would consist of (C 5 Me 5 ) 2 Sm(III) and deprotonated organic acids. The chain transfer polymerization was confirmed by turnover numbers (TON). tert-Butyl thiol exhibited the chain transfer reactivity effectively to control the molecular weight of PMMA without decreasing of the polymer yield and the stereoregularity. As a result of this chain transfer polymerization, thermal and optical propertics of the PMMA obtained were improved by the control of chain end groups or by reducing a large amount of the samarium initiator.