Poly(1-butene) was obtained by polymerization of 1-butene at 100 degrees C using rac-(dimethylsilyl)bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride (1) as catalyst and methylaluminoxane (MAO) as cocatalyst. The product was characterized by NMR (H-1 and C-13), size exclusion chromatography (SEC), and vapor pressure osmometry (VPO). The number-average molecular weight of the polymer was determined as 1910, 2025, and 2055 by SEC, VPO, and NMR, respectively. The poly(1-butene) is 84% isotactic and has high regioselectivity (ca. 95% 1,2-addition). Both saturated and unsaturated end groups were characterized by NMR. Vinylidene and trisubstituted double bonds comprise approximately 67% and 29%, respectively, of the unsaturated end groups with the remainder consisting of vinylene, vinyl, and tetrasubstituted double bonds. n-Butyl and sec-butyl groups constitute the saturated end groups in the approximate ratio 10:1. There is a slight excess of saturated end groups relative to unsaturated end groups. These results are discussed in terms of a reaction mechanism of initiation and propagation with Various chain-transfer reactions (beta-hydride transfers with and without rearrangement, transfer to aluminum, transfer to vinylidene end groups, and beta-alkyl transfer).