The organo-rare-earth-metal-initiated living polymerization of methyl methacrylate (MMA) was first discovered in 1992 with (C5Me5)(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 X 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 l-hexene with MMA, methyl acrylate, cyclic carbonate, or epsilon -caprolactone in a voluntary ratio. Highly isotactic (97%), monodisperse, high molecular weight (M-n > 500 X 10(3), M-w/M-n < 1.1) PMMA was first obtained in 1998 with [(Me3Si)(3)C](2)Yb. Stereocomplexes prepared by the mixing of the resulting syndiotactic and isotactic PMMA revealed improved physical properties.