Thesis (M.Sc.)--Chulalongkorn University, 2000

Half-titanocene catalysts (cyclopentadienyltitanium trichloride and pentamethylcyclopenta-dienyltitanium trichloride) were used to catalyze the polymerization of styrene. The cocatalysts used are based on boron compounds; tris (pentaflurophenyl) boron and triphenylcarbenium tetrakis (pentaflurophenyl- borate) with aluminium compounds (trimethylaluminium or triisobutylaluminium) as an alkylating agent. The factors affecting polymerization were studied: types of catalyst and cocatalyst, polymerization temperatures and time, Al/Ti ratio. The experimental results reveal that the optimum conditions are: temperature of 65 ํC, polymerization time of 20 hours, Al/Ti ratio of 300. Comparison between the two catalysts: cyclopentadienyltitanium trichloride and pentamethylcyclopentadienyltitanium trichloride showed that electron releasing group on the ligand increases the catalytic activity. Among the various catalytic systems tested, the pentamethylcyclopentadienyltitanium trichloride with triisobutylaluminium was found the best system for producing polystyrene with 73% syndiotacticity, This single-site catalyst allows the control of polymer structure, which was revealed from the FT-IR spectrum, and % syndiotacticity determination. In addition, the molecular weight distribution of the polymer is narrow (1.8) which is the advantage of this type of catalyst.