ISSN:
0360-6376
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Polymerization of ethylene was initiated with soluble polystyrene100-butadiene3-Li/TiCI4 complexes in toluene leading to block copolymers. The activity of the system was measured at a constant ratio r = [Li]/[Ti] and for different concentrations in active centers and in monomer. Measurement of the amount of the block copolymers formed led to the direct determination of the efficiency of the catalytic system. This efficiency is defined with respect to the number of potentially active centers and is close to 90%. From both measured values of activity of the catalytic system and of its efficiency, the rate constants of propagation were deduced. The kinetic behavior of the system is fully consistent with that of a living system. The rate is first order towards both ethylene and active centers concentrations. So, the rate constant of propagation is an absolute rate constant, measuring the intrinsic reactivity of active sites. Determination of the absolute rate constant at different temperatures, led to thermodynamic parameters of the propagation reaction. The chemical composition of the complex and the absence of polymeric aggregation, leads to propose a structure of the active species: a bioctahedral binuclear structure is consistent with kinetic, thermodynamic results, and structural determinations.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1984.170221224
