ISSN:
0887-624X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Polymerizations of ethylene by the MgCl2/ethylbenzoate/p-cresol/AlEt3 TiCl4-AlEt3/methyl-p-toluate (CW-catalyst) have been studied. The initially formed active site concentration, [Ti1*] has a maximum value of 50% of total titanium at 50°C and lower values at other temperatures. The Ti1* decays rapidly to Ti2* sites with conc. ca. 10 mol %/mol Ti. The rate constants for four chain transfer processes have been obtained at 50°C: for transfer with AlEt3, ktr, 1A = 2.1 × 10-4 s-1 and ktr, 2A = 4.8 × 10-4 s-1; for transfer with monomer, ktr, 1M = 3.6 × 10-3 (M s)-1 and Ktr, 2M = 8.3 × 10-3 (M s)-1; for β-hydride transfer, ktr, 1β = 7.2 × 10-4 s-1 and ktr, 2β = 4.9 × 10-4 s-1; and transfer with hydrogen, ktr, 1H = 4.0 × 10-3 torr1/2 s- and ktr, 1H = 5.1 × 10-3 torr1/2 s-1. The rate constants for the termination assisted by hydrogen is ktr1H = 1.7 (M1/2 torr1/2 S)-1. If monomer is assisting termination as was observed for propylene polymerization, then ktM = 7.8 (M3/2 s)-1. Values of all the rate constants can be higher or lower at other temperatures. Detailed comparisons were made with the results of propylene polymerizations. There are more than four times as many Ti1* active sites for ethylene polymerization than there are for stereospecific polymerization of propylene; the difference is more than a factor of two for the Ti2* sites. Certain rate constants are nearly the same for both monomers while others are markedly different. Some of the differences can be explained by stereoelectronic effects.
Additional Material:
19 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pola.1986.080241010
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