Polymerization kinetics of butadiene in the presence of secondary butyl-lithium

Abstract

The polymerization kinetics of butadiene initiated by sec.butyl-lithium have been studied in detail by dilatometry in heptane, cyclohexane, and toluene in the temperature range 20–60°C, a vacuum method being used and the walls of the apparatus employed being rinsed with a solution of the organo-lithium catalyst. The ways in which the polymerization rate and the molecular weights of the polymers depend on the concentration of sec.C 4H 9Li at 20 and 60°C have been found for the three solvents with active site concentrations in the range 1 × 10 −2−1 × 10 −5 mole/l.; the apparent activation energies for chain propagation have been determined. It has been shown that the order of the chain propagation reaction with respect to the catalyst depends not only on the polymerization temperature and the sec.C 4H 9Li concentration, but also on the type of hydrocarbon solvent being used. It is suggested that, during polymerization in aliphatic solvents as distinct from aromatic solvents, the degree of association of the active sites does not correspond to the observed order of the reaction with respect to the catalyst since, in this case, associated forms of the organo-lithium compounds also participate in chain propagation acts in addition to the monomeric forms.