LONG-CHAIN BRANCHING IN ETHYLENE POLYMERIZATION USING CONSTRAINED GEOMETRY METALLOCENE CATALYST

We report an experimental investigation on long chain branching (LCB) in ethylene polymerization with the Dow Chemical's constrained geometr y catalyst system, CGC-Ti/TPFPB/MMAO, using a continuous stirred-tank reactor (CSTR) at 140 degrees C, 3.45 x 10(3) kPa, and a mean residenc e time (tau) of 4 min. The effects of the catalyst (CGC-Ti) and co-cat alyst (TPFPB and MMAO) concentrations on the catalyst activity, polyme r molecular weight, and shear thinning were systematically examined. T he boron cocatalyst had a great influence on the CGC activity. Increas ing the ratio TPFPB/CGC-Ti from 0.66 to 5 gave ethylene propagation ra tes from 1.65 x 10(3) to 1.36 x 10(1) L.mol(-1).s(-1). The addition of MMAO appeared to be essential, most likely acting as an impurity scav enger. The LCB polyethylenes showed enhanced shear thinning properties . The melt flow index ratios I-10/I-2 were in the range of 6.96 to 23. 4, with the I-2 of 0.172 to 0.681 g/10 min. The weight-average molecul ar weight (M) over bar(W), was correlated to I-2 using a power equatio n within narrow I-10/I-2 ranges. The exponential factors were in the r ange of 4.24 to 6.31. The experimental and calculated (M) over bar(W)' s were in a good agreement.