Propylene was copolymerized with 7-methyl-1,6-octadiene, 1,9-decadiene and alpha-olefins using dimethylsilanylbis(2-methyl-4-phenyl-1-indenyl)zirconium dichloride supported on methylaluminoxane modified silica. Additional methylaluminoxane was needed to activate the catalyst. Comonomer incorporations were 1.5 mol% or less. In propylene/7-methyl-1,6-octadiene copolymers there was no indication of long-chain branching and molar masses were low. Adding a small amount of 1,9-decadiene caused very high molar masses and broad molar mass distributions. A possible long-chain branching in propylene/1,9-decadiene copolymers was evaluated by stress-controlled dynamic rheometer. Changed rheological behavior and especially raised Arrhenius-type flow activation energy along with change in polymer properties indicated long-chain branching in propylene/1,9-decadiene copolymers. (C) 2004 Elsevier Ltd. All rights reserved.