Electron spin resonance spectroscopy study on reduction of constrained‐geometry catalyst systems

Abstract The reduction of a constrained‐geometry catalyst (CGCTiMe 2 ) activated with a series of cocatalysts, including modified methylaluminoxane (MMAO), tris(pentafluorophenyl) borane [B(C 6 F 5 ) 3 ], and combined B(C 6 F 5 ) 3 /MMAO, was experimentally investigated using an on‐line electron spin resonance spectroscopy (ESR) technique. The effects of the solvent type, cocatalyst/catalyst ratio, and temperature on the reduction were examined. In the CGCTiMe 2 /MMAO system, increasing the Al/Ti molar ratio from 20 to 250 significantly increased the Ti(III) content. Adding trimethylaluminum to the system lowered the Ti(III) content. Three trivalent Ti species, Ti(a) (g = 1.972), Ti(b) [g = 1.992, α(H) = 7.4 G], and Ti(c) (g = 1.995), were observed. In the CGCMe 2 /B(C 6 F 5 ) 3 system, only one trivalent Ti species (g = 1.988) was observed. The CGCTiMe 2 /B(C 6 F 5 ) 3 system was more stable to reduction than the CGCTiMe 2 /MMAO system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2474–2482, 2003