Kinetics of reaction of metal alkyls with alkenes. Part 7.—n-Butyl lithium and N:N:N′:N′-tetramethyl ethylene diamine with butadiene
The polymerization of butadiene, initiated by the complexes of n-butyl lithium and tetramethyl ethylene diamine, has been studied in the range 230–280 K by dilatometry. Initial rates of polymerization were second order in monomer, and first in both amine and butyl lithium concentrations. Maximum rates were observed at molar ratios of lithium alkyl/amine below 1/2. Rates of polymerization decreased with conversion, consistent with first-order dependence on unconverted monomer. Molecular weights of the polymers increased with conversion, and at ratios below 1/2 in alkyl/amine compared exactly with moles of monomer consumer per mole of butyl lithium initially present. The micro-structure of the polymers varied with polymerization temperatures between 70–90 % of 1,2 addition product. All the polymers had narrow molecular weight distributions independent of the final degree of conversion.
It was concluded that the polymerization of butadiene occurred by a “living” anionic addition mechanism, initiated by the 1/2 amine complex. The nature of the active polymerizing species was confirmed by a molecular weight study of the complexes present at various molar ratios, and their concentration dependence.