Journal of Polymer Science Part A: Polymer Chemistry, Vol.37, No.15, 2949-2957, 1999
Continuous solution copolymerization of ethylene and octene-1 with constrained geometry metallocene catalyst
The solution copolymerization of ethylene (1) with octene-1 (2) in Isopar E using constrained geometry catalyst system, [C5Me4((SiMe2NBu)-Bu-t)]TiMe2 (CGC-Ti)/ tris(pentafluorophenyl)boron (TPFPB)/modified methylaluminoxane (MMAO), has been carried out in a high-temperature, high-pressure continuous stirred-tank reactor (CSTR) at 140 degrees C, 500 psig and with a mean residence time of 4 min. A series of copolymer samples with octene-1 content up to 0.337 mole fraction were synthesized and characterized. The estimated reactivity ratios were r(1) = 7.90 and r(2) = 0.099. The CGC-Ti showed a higher ability to incorporate high cu-olefins than other metallocene catalysts investigated in the literature due to its open structure. The presence of octene-1 lowered the catalyst activity, particularly at octene-1 levels higher than 0.45 mole fraction. Octene-1 was also found to reduce the molecular weight of polymer and broaden the molecular weight distributions. The triad distributions were measured by C-13-NMR. A minor penultimate effect was observed. The penultimate octene-1 unit appeared to slow down monomer insertion rates. A comparison of the propagation rate of octene-1 with the incorporation rate of macromonomer in the homopolymerization of ethylene suggests that the addition of macromonomer is effectively instantaneous after it is generated with diffusion to or from the active center reaction volume playing a minor role.
Keywords:metallocene polymerization;linear low density polyethylene;ethylene/octene-1 copolymerization;constrained geometry catalyst;continuous solution polymerization;branching;reactivity ratio