Long chain branching in ethylene polymerization using constrained geometry metallocene catalyst

Abstract

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.

A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

“…[73] Recently, however, Wang and co-workers [183] found that LCB had considerable effects on the nonisothermal crystallization of PE samples in the DSC study of long-chain branched PEs (LCBD up to 0.44C/1000 Cs) prepared by CSTR technique with CGC-Ti catalyst. [9] The crystallization enthalpy and the ultimate crystalline degree decreased with increasing LCBD. At relatively low cooling rates, a small amount of long-chain branches could promote crystal nucleation but reduce growth rate due to restraints of LCB on chain movement or diffusion.…”

“…These values give an average LCBD of the whole polymer sample. [8] Wang et al used 13 C NMR to measure LCBD of PEs produced by CGC-Ti [9] and Cp 2 ZrCl 2 catalysts. [10] Figure 1 shows that the resonance peaks of α and β methylene, as well as methine carbons, could be found in the 13 C NMR spectrum of a PE sample produced by MMAO/Cp 2 ZrCl 2 due to the formation of LCBs.…”

“…In the integration, the baseline effect caused by "tree trunks" of the peak δδ + should be subtracted from the signals. [9,10] In addition to measuring the degree of LCBD, 13 C NMR can be used to study the saturated chain end density (the number of saturated chain ends per carbon), unsaturated chain end density (the number of unsaturated chain ends per carbon), LCB frequency (LCBF, the number of branching points per polymer molecule) and the concentration of unreacted macromonomers. These parameters combined with kinetic results can be used to estimate various rate constants, such as k LCB (LCB), k β (β-hydride C NMR spectrum with the chemical shifts in TCB and d-ODCB at 120 °C of a semibatch produced PE sample.…”

“…[115] I 10 /I 2 can be used to study the degree of LCB of POs. [5,9,73] are linear copolymers. [76] (Reproduced with permission.…”

Temperature rising elution fractionation and characterization of ethylene/octene-1 copolymers synthesized with constrained geometry catalyst

“…The recent advent of the single-site type metallocene technology provides copolymers with narrow MWD and composition distributions 11,12) . A new type of metallocene, called constrained geometry catalyst (CGC) 13,14) , offers ready incorporation of a -olefins and ethylene macromonomers generated via b -hydride elimination and/or transfer to monomer to synthesize branched polyolefins and LLDPEs [15][16][17] . Such branched polymers and LLDPE's have an excellent combination of good mechanical properties and processibilities 18) .…”