The ligand effects of homogeneous Ti-based catalysts for the copolymerization of styrene ([M-1]) with 4-[(tert-butyldimethylsilyl)oxy] styrene (TBDMSS; [M-2]) were investigated by the UV/visible spectroscopic analysis. Concerning the higher yields from the copolymerization of styrene with TBDMSS, the half-sandwich type of titanocene having pi-ligands compared to titanium (TV) butoxide (Ti(OBu)(4)) having a-ligands was a more effective catalysts. The silyloxy group exhibiting a negative a value in the Hammett sigma-rho relationship reduced the activities of titanocenes. The stronger electron-donating substituent on the iz-ligand leading to the increase in the catalytic activity in syndiospecific polymerization of styrene contributed to the decrease of the reactivity of the "cationlike" metal center due to both electronic and steric effects. The reactivity ratios, r(1) and r(2), in the eta(5)-indenyl trichlorotitanium ((Ind)TiCl3)-catalyzed copolymerization of styrene with TBDMSS in the presence of methylaluminoxane (MAO) ([Al]/[Ti] = 2000) were 0.997 and 7.27 from the evaluation of Finmann and Ross, respectively. The r(1)r(2) product value (7.25) indicates that a block type of copolymer may be produced in a relatively high feed range of TBDMSS to styrene.