Anionic or neutral allylic samarium or neodymium species catalyse the polymerization of styrene (catalyst/styrene ratio = 1:1000) without addition of a cocatalyst. Random syndiotacticrich material is obtained from tetra-allyllanthanides, whereas neutral trisallyl-lanthanides or anionic ansa-bis(cyclopentadienyl)bisallyl-lanthanides afford isotactic-rich polystyrene.

Anionic or neutral allylic samarium or neodymium species catalyse the polymerization of styrene (catalyst/styrene ratio = 1:1000) without addition of a cocatalyst. Random syndiotactic‐rich material is obtained from tetra‐allyl‐lanthanides, whereas neutral trisallyl‐lanthanides or anionic ansa‐bis(cyclopentadienyl)bisallyl‐lanthanides afford isotactic‐rich polystyrene. Copyright © 1999 John Wiley & Sons, Ltd.