Kinetics of Long Chain Branching in Continuous Solution Polymerization of Ethylene Using Constrained Geometry Metallocene

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.

Properties of aliphatic polyesters withn-paraffinic side branches

“…The discrepancy between the shear thinning behavior of the aliphatic polyesters and that of the ethylene copolymers comes from the fact that longchain branches were formed by the CGCT catalyzed copolymerization of ethylene and 1-octene with the in situ-produced vinyl terminated polyethylene, due to the chain termination by ␤-hydride elimination and/or transfer to monomers, because long-chain branched polymers have higher shear sensitivity compared to the linear counterparts. Wang et al 13 observed long-chain branches up to 0.44/10,000 carbons were formed during ethylene homopolymerization with CGCT in a continuous stirred-tank reactor operating at 35 atm and 140 -190°C. Figure 6 are cole-cole plot results, 14 -17 respectively, for PBSD and PEAD.…”

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

“…elimination), k fM (transfer to monomer), and k fH (transfer to hydrogen). [12] The ratio between saturated and unsaturated chain ends is an important parameter for the study of chain transfer in the polymerization. [13] For PP systems, 13 C NMR analysis is also capable of revealing the stereo environment at the branching point.…”

“…A period of 20 hours at 75.4 MHz with a delay time of 10 s between pulses and more than 7000 scans was reported in Wang's work, to obtain 13 C NMR spectra with an acceptable resolution and signal-to-noise ratio. [12] To double the signal to noise ratio, the number of scans must be quadrupled, which dramatically increases to the acquisition time. A result of this is that an acquisition time of 1-46 days is required to obtain an accurate estimate of LCBD in the range of 0.2-1.0 branches per 10 000 carbons using high field solutionstate NMR (600 MHz, 1 H resonance).…”

“…[12,58,59] Therefore, it is proper to use Equation (20) to calculate the LCBF in long-chain branched PEs. With the obtained LCBF values, the LCBD can be calculated as…”

Synthesis and Properties of Syndiotactic Graft Copolymer of Styrene with Polyisoprene Macromonomer by CpTiCl3–Methylaluminoxane Catalyst

“…The copolymerization of St and SIPM proceeded readily by titanium compounds-MAO catalysts giving powdered products in high yields, although catalytic activity was sensitive to the titanocene compounds examined. The structure of MEK-insoluble fraction of the graft copolymer was confirmed by 13 C and 1 H NMR spectroscopy to be the graft copolymer having a high syndiotacticity of the main chain and well-defined polyisoprene of the side chain as described previously. 34 From Table II, the electron-withdrawing chloro ligands of the half metallocene are favorable to produce syndiotactic polymers.…”