This paper deals with the preparation and olefin polymerization catalysis of six new divalent samarium complexes. These bridged bis(cyclopentadienyl) (Cp) complexes exhibit various structures with regard to the bridging group and the position of substituents on the Cp rings:  rac-tBu, Me2Si(2-Me3Si-4-tBuC5H2)2Sm(THF)2 (7); rac-tBuMe2Si, Me2Si(2-Me3Si-4-tBuMe2SiC5H2)2Sm(THF)3 (8); C 1 symmetric, Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]Sm(THF)2 (9); meso, [1,2-(Me2Si)(Me2SiOSiMe2)](3-tBuC5H2)2Sm(THF)2 (10); C 2 v symmetric (Ph2Si), Ph2Si[3,4-(Me3Si)2C5H2]2Sm(THF)2 (11); C 2 v symmetric [(SiOSi)2], [1,2-(Me2SiOSiMe2)2](3-tBuC5H2)2Sm(THF)2 (12). The structures of 7, 8, 10, and 12 were confirmed by X-ray crystallographic analysis. Among these divalent complexes, meso type complex 10 showed the highest activity for polymerizations of ethylene (5 × 105 g of PE/(mol h)) and C 1-symmetric 9 afforded the highest molecular weight of polyethylene (M n = 145 × 104). Only racemic complexes 7 and 8 could polymerize 1-olefins such as 1-pentene and 1-hexene, giving highly isotactic polymers. Moreover, rac-7 induces catalytic cyclopolymerization of 1,5-hexadiene to give poly(methylene-1,3-cyclopentane).

Diblock copolymerizations of L‐ or D,L‐lactide (LA) with trimethylene carbonate (TMC) or 2,2‐dimethyltrimethylene carbonate (2,2‐DTMC) with SmMe(C5Me5)2‐(tetrahydrofuran) as an initiator and triblock copolymerizations of L‐ or D,L‐LA/cyclic carbonates/L‐ or D,L‐LA with [Sm(C5Me5)2]2(PhCCCCPh) as an initiator generated the desired block copolymers. This article describes the comparison of biodegradabilities by proteinase K and a compost and mechanical properties between the resulting di‐ or triblock copolymers and random copolymers composed of L‐ or D,L‐LA and cyclic carbonates. The scanning electron microscopic profiles of resulting polymers were measured to understand the morphological change during biodegradation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3572–3588, 2003

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 at a living chain end 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 (C5Me5)2Sm(III) and deprotonated organic acids. The chain transfer polymerization were 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 properties of the PMMA obtained were improved by the control of chain end groups or by reducing a large amount of the samarium initiator.

No abstract