No abstract

Our high-temperature and high-pressure continuous stirred-tank reactor (CSTR) has been used for the polymerization of ethylene with the constrained geometry metallocene system, [C5-Me4(SiMe2N t Bu)]TiMe2 (CGC-Ti)/ tris(pentafluorophenyl)boron (TPFPB)/ modified methylaluminoxane (MMAO), in Isopar E solution at 500 psig. Polyethylenes (PE) with long chain branching (LCB) densities up to 0.44 carbons/10 000 carbons, melt flow index ratios of 7.4-25.7, and narrow polydispersity indexes about 2 were synthesized. The polymerization variables included temperature, mean residence time, and ethylene feed concentration. Polyethylene chains terminated mainly by transfer to monomer yielded macromonomers for the LCB formation. The CGC-Ti catalyst appeared to be single site type, and active centers showed an exponential decay with mean residence time. The rate constants and their activation energies of the ethylene propagation, LCB, chain transfer to monomer, and chain transfer to hydrogen were estimated. The presence of methyl side chains in PEs produced at elevated temperatures indicated that the open structure of CGC-Ti catalyst allowed macromonomers to have 2,1-insertion.

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 Mw 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 Mw's were in a good agreement.

The electrochemical synthesis of a free-standing film of polypyrrole, using commonly available equipment and materials, is described at a level suitable to application in a general chemistry laboratory. Also described are methods to quantitatively assess the doping level and to characterize the polymer film in terms of its conductivity as a function of temperature.

SUMMARY We report an experimental investigation on long chain branching (LCB) in ethylene polymerization with the Dow Chemical's constrained geometry catalyst system, CGC-TflPFPBMMAO, using a continuous stirred-tank reactor (CSTR) at 140°C, 3.45 x lo3 kPa, and a mean residence time (5) 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 x lo3 to 1.36 x lo4 L -mol-l * s-I. 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 I& were in the range of 6.96 to 23.4, with the 12 of 0.172 to 0.681 g/10 min.The weight-average molecular weight a, was correlated to I, using a power equation within narrow I& ranges. The exponential factors were in the range of 4.24 to 6.3 1. The experimental and calculated Mw's were in a good agreement.