| Abstract: | We report an experimental investigation on long chain branching (LCB) in ethylene polymerization with the Dow Chemical's constrained geometry catalyst system, CGC-Ti/TPFPB/MMAO, using a continuous stirred-tank reactor (CSTR) at 140°C, 3.45 × 103 kPa, and a mean residence time (τ) of 4 min. The effects of the catalyst (CGC-Ti) and co-catalyst (TPFPB and MMAO) concentrations on the catalyst activity, polymer molecular weight, and shear thinning were systematically examined. The boron cocatalyst had a great influence on the CGC activity. Increasing the ratio TPFPB/CGC-Ti from 0.66 to 5 gave ethylene propagation rates from 1.65 × 103 to 1.36 × 104 L · mol−1 · s−1. The addition of MMAO appeared to be essential, most likely acting as an impurity scavenger. The LCB polyethylenes showed enhanced shear thinning properties. The melt flow index ratios I10/I2 were in the range of 6.96 to 23.4, with the I2 of 0.172 to 0.681 g/10 min. The weight-average molecular weight M w was correlated to I2 using a power equation within narrow I10/I2 ranges. The exponential factors were in the range of 4.24 to 6.31. The experimental and calculated M w's were in a good agreement. |
