Rare‐earth‐metal‐initiated polymerizations of (meth)acrylates and block copolymerizations of olefins with polar monomers

The organo‐rare‐earth‐metal‐initiated living polymerization of methyl methacrylate (MMA) was first discovered in 1992 with (C 5 Me 5 ) 2 LnR (where R is H or Me and Ln is Sm, Yb, Y, or La) as an initiator. These polymerizations provided highly syndiotactic (>96%) poly(methyl methacrylate) (PMMA) with a high number‐average molecular weight ( M n > 1000 × 10 3 ) and a very narrow molecular weight distribution [weight‐average molecular weight/number‐average molecular weight ( M w / M n ) < 1.04] quantitatively in a short period. Bridged rare‐earth‐metallocene derivatives were used to perform the block copolymerization of ethylene or 1‐hexene with MMA, methyl acrylate, cyclic carbonate, or ϵ‐caprolactone in a voluntary ratio. Highly isotactic (97%), monodisperse, high molecular weight ( M n > 500 × 10 3 , M w / M n < 1.1) PMMA was first obtained in 1998 with [(Me 3 Si) 3 C] 2 Yb. Stereocomplexes prepared by the mixing of the resulting syndiotactic and isotactic PMMA revealed improved physical properties.