Catalogo Articoli (Spogli Riviste)

OPAC HELP

Titolo:
Triisobutylaluminum as cocatalyst for zirconocenes. I. Sterically opened zirconocene/triisobutylaluminum/perfluorophenylborate as highly effective ternary catalytic system for synthesis of low molecular weight polyethylenes
Autore:
Panin, AN; Sukhova, TA; Bravaya, NM;
Indirizzi:
Russian Acad Sci, Inst Problems Chem Phys, Chernogolovka 142432, Moscow Region, Russia Russian Acad Sci Chernogolovka Moscow Region Russia 142432 Region, Russia
Titolo Testata:
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY
fascicolo: 11, volume: 39, anno: 2001,
pagine: 1901 - 1914
SICI:
0887-624X(20010601)39:11<1901:TACFZI>2.0.ZU;2-C
Fonte:
ISI
Lingua:
ENG
Soggetto:
OLEFIN POLYMERIZATION; PROPYLENE POLYMERIZATION; ETHYLENE POLYMERIZATION; DICHLORIDE COMPLEXES; ALUMINUM COMPOUNDS; ANCILLARY LIGAND; CHAIN TRANSFER; ACTIVE-SITES; METALLOCENE; KINETICS;
Keywords:
metallocene catalysts; ethylene polymerization; ethylene oligomerization; kinetics; branched polyethylene; perfluorophenyl borates; trialkylaluminums;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
46
Recensione:
Indirizzi per estratti:
Indirizzo: Bravaya, NM Russian Acad Sci, Inst Problems Chem Phys, Chernogolovka 142432, Moscow Region, Russia Russian Acad Sci Chernogolovka Moscow Region Russia 142432 ia
Citazione:
A.N. Panin et al., "Triisobutylaluminum as cocatalyst for zirconocenes. I. Sterically opened zirconocene/triisobutylaluminum/perfluorophenylborate as highly effective ternary catalytic system for synthesis of low molecular weight polyethylenes", J POL SC PC, 39(11), 2001, pp. 1901-1914

Abstract

Ethylene polymerizations with catalytic systems Me2SiCp*NttBuZrX(2) (1) [Cp* = C-5(CH3)(4); X = Cl(1Cl), Me (1Me)], triisobutylaluminum (TIBA), perfluorophenylborate CatB(C6F5)(4) [Cat = CPh3 (3), Me2NHPh (4)], or Me2SiCp2ZrX2 [X = Cl(2Cl), Me (2Me)]/TIBA/3 (4) were performed within a wide range ofethylene pressures of different Al/Zr ratios, and Zr/B = 1. Catalytic systems 1Cl(2Cl)/TIBA/3 led to the formation of very high linear molecular weight polyethylene (PE) of M-eta similar to2,000,000 with low activity. The replacement of both chlorine ligands in the precatalyst for the methyl ones led to the formation of active species producing low molecular weight PE with high activity. Chain transfer to ethylene was shown to be the main reaction controlling PE chain propagation: k(p)/k(tr) similar to 20-30 for 1Me/TIBA/3 and k(p)/k(tr) similar to 350-500 for 2Me/TIBA/3. It was suggested that TIBA was present in the active center first in the form of a neutral heterobimetallic Zr-Al bridged complex followed by the formation of a partiallypolarized Zr-Al(Cl)R-2 (R = Bu-i) or an unreactive Zr-AlR3 cationic complex by abstraction of the alkyl ligand under the action of berate. It was concluded that AIR, from the latter cationic complex may be easily reversibly replaced under the specific coordination of ethylene or accumulated alpha -olefin, giving rise to highly labile and sterically accessible cationic species. Experiments on ethylene polymerization with the catalytic systems 1Cl(1Me)/TIBA/3/Ph2NH, 1Cl(1Me)/TIBA/4, 2Cl(2Me)/TIBA/3/ Ph2NH, and 2Cl(2Me)/TIBA/4 were performed to confirm the suggestion. Catalytic systems derived from dichloride complexes in the presence of a sigma -donor substrate also produced low molecular weight PEs with molecular weight characteristics similar to those of products obtained with the dimethylated precatalysts. The specific feature of active species derived from 2Me complexes to isomerize coordinated alpha -olefin into trans-vinylene polymer chains was also revealed. The catalytic behavior of the ternary catalytic system based on 2ME relative to 2Me or 2Cl precatalysts activated with polymethylaluminoxane at different Al/Zr ratios was compared. (C) 2001 John Wiley & Sons, Inc.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 31/10/20 alle ore 03:27:15