ISSN:
0360-6376
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The reaction between tert-butylchloride (t-BuCl) and dimethylcyclopentadienylaluminum (Me2AlCPD) was studied as a model for initiation by the tert-butyl cation (t-Bu⊕) and termination by cyclopentadienylation by the Me2Al(CPD)Cl⊖ counteranion of isobutylene polymerization. All reaction products formed in this model system have been identified and quantitatively determined. A comprehensive scheme that indicates pathways to these products was developed (scheme III). It is proposed that the predominant product, tert-butylcyclopentadiene (t-BuCPD), arises in the collapse of the t-Bu⊕-Me2Al(CPD)Cl⊖ ion pair, mainly by CPD⊖ transfer to the tert-butyl cation. The minor products are neopentane (t-BuMe) and isobutylene (i-C4H8), which are probably formed, respectively, by Me⊖ transfer to and proton loss from the t-butyl cation. Cyclopentadienylation selectivity increases by lowering the temperature and extrapolation of results suggests 100% cyclopentadienylation at -55°C. The t-BuCl/Me2AlCPD ratio strongly influences the overall reaction pathway. The reaction is first order in t-BuCl with ΔEa of ca. 7 kcal/mole (1,2-dichloroethane or chlorobenzene solvents, +24 to -29°C). Indirect evidence indicates that the kinetic product of cyclopentadienylation is 5-t-BuCPD and that this isomer cannot be tert-butylated; that is, the initiation of 5-t-BuCPD polymerization by t-Bu⊕ is sterically unfavorable. Detailed analysis of the chemistry and kinetics of the t-BuCl/Me2AlCPD model system holds important clues to the controlled polymerization of olefins leading to macromolecules with cyclopentadiene (CPD) termini.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1979.170170714
