Synthesis of branched polyethylenes by the tandem catalysis of silica‐supported linked cyclopentadienyl‐amido titanium catalysts and a homogeneous dibromo nickel catalyst having a pyridylimine ligand

The synthesis of branched polyethylenes by ethylene polymerization with new tandem catalyst systems consisting of methylaluminoxane‐preactivated linked cyclopentadienyl‐amido titanium catalysts [Ti(η⁵:η¹‐C₅Me₄SiMe₂NR)Cl₂ (R = Me or ^tBu)] supported on pyridylethylsilane‐modified silica (PySTiNMe and PySTiN^tBu) and homogeneous dibromo nickel catalyst having a pyridyl‐2,6‐diisopropylphenylimine ligand (PyminNiBr₂) in the presence of modified methylaluminoxane was investigated. Ethylene polymerization with only PyminNiBr₂ yielded a mixture of 1‐ and 2‐olefin oligomers with methyl branches [weight‐average molecular weight (M_w) ～ 460)] with a ratio of about 1:7. By the combination of this nickel catalyst with PySTiN^tBu, polyethylenes with long‐chain branches (M_w = 15,000–50,000) were produced. No incorporation of 2‐olefin oligomers was observed in the ¹³C NMR spectra. Unexpectedly, the combination of the nickel catalyst with PySTiNMe produced lower molecular weight polyethylenes with only methyl branches. The molecular weight distributions of branched polyethylenes obtained with both PySTiNMe and PySTiN^tBu combined with the nickel catalyst were broad (weight‐average molecular weight/number‐average molecular weight < 9). Bimodal gel permeation chromatography (GPC) curves were clearly observed in the PySTiNMe system, whereas GPC curves with small shoulders in low molecular weight areas were observed for PySTiN^tBu. The synthesis of branched polyethylenes with tandem catalyst systems of corresponding homogeneous titanium catalysts and the nickel catalyst was also investigated for comparison. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 528–544, 2003     

Synthesis and properties of widely conjugated polyacetylenes having anthryl and phenanthryl pendant groups

The metathesis polymerization of 1- and 2-ethynylanthracenes (1-EA and 2-EA) and 2- and 3-ethynylphenanthrenes (2-EP and 3-EP) in the presence of various WCl₆-based catalysts produced widely conjugated soluble polymers with relatively high molecular weights. The highest weight-average molecular weights of poly(1-EA) and poly(2-EA) reached 61,000 and 26,000, respectively, when Ph₄Sn was used as cocatalyst, while those of poly(2-EP) and poly(3-EP) reached 23,000 and 65,000, respectively, with Ph₃Bi as cocatalyst. In contrast, MoCl₅-based catalysts were hardly or not effective for these monomers. A large red-shifted peak was observed centering at 570 nm (the cutoff at 750 nm) in the absorption spectrum of poly(1-EA), while the red-shifted peaks were seen around 500 nm (the cutoffs near 700 nm) in the spectra of other polymers, indicating wide conjugations of the polymer chains. The configurational structures of all the polymers confirmed by DSC and ¹H-NMR were trans structures. However, poly(1-EA) and poly(3-EP) appeared to consist partly of cis structures in their main chains. All of the present polymers showed relatively high thermal stability in air compared with poly(phenylacetylene). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3131–3137, 1998     

Poly(4‐vinylpyridine)‐supported cationic bis(cyclopentadienyl)zirconocene catalyst: Development of a new simple method to prepare polymer‐supported cationic zirconocene and its application to ethylene polymerization

Bis(cyclopentadienyl)zirconocene dimethyl (Cp₂ZrMe₂) combined with triphenylcarbenium tetrakis(pentafluorophenyl)borate ([Ph₃C][B(C₆F₅)₄]) was brought into contact with a suspension of 2% cross‐linked poly(4‐vinylpyridine) to give a new type of polymer‐supported cationic zirconocene catalyst. The resulting polymer‐supported catalyst system combined with Al(i‐Bu₃) showed markedly high activity for ethylene polymerization in even a non‐polar solvent like hexane at 25–60°C and [Al]/[Zr] molar ratio 40–200. By the analysis of Zr content of the hexane solution, it was found that no Zr was detected in the solution, i. e. no leaching of the cationic catalyst into the hexane medium. The catalytic activity was found to increase with an increase of polymerization temperature and showed the highest at [Al]/[Zr] = 100. The molecular weight, crystalline melting temperature, crystallinity, and bulk density of polyethylene formed were higher than those of the polymer obtained from the homogeneous system.