Styrene was isospecifically polymerized on dichloro[1,4-dithiabutandiyl-2,2'-bis(6-tert-butyl-4-methylphenoxy)] titanium (1) activated with methylaluminoxane in the presence of monoolefins such as 1-hexene, cyclopentene, and norbornene and nonconjugated diolefins such as 1,9-decadiene, 1,7-octadiene, and dicyclopentadiene. The molecular weight of isotactic polystyrene was varied from 2000 to 600 000 g/mol as a function of the olefin/styrene molar ratio without sacrificing high catalyst activities. Chain transfer constants were determined, with the highest values found for linear mono- and nonconjugated diolefins. In contrast to norbornene, I-olefin incorporation was very low. End groups were identified by means of C-13 NMR investigations of polymers containing C-13-labeled 1-octene. Olefin- and diolefin-terminated isotactic polystyrenes including novel vinyl-terminated macromonomers were obtained in high yields.