Quantitative Evaluation of Moderating Effect of Several 1, 4-Dienes on Molecular Weight in the Polymerization Catalysed by Alfin

Abstract

The quantitative evaluation of moderating effect of several 1, 4-dienes on molecular weight was done by determining the chain transfer constant for the polymerization of butadiene catalysed by Alfin. The order of the chain transfer constant is as follows, 1, 4-dihydrona phthalene (8.96 X 1O^-3) > 1, 4-pentadiene (2.32 x 10^-3) > 1, , elhexadiene (1.77 X 10^-3) > 3-methyl 1, 4-pentadiene (1.68 x 10^-3) >allylbenzene (1.26 x 10^-3) > 1, 4-cyclohexadiene (1.15 x 10^-3).
The same order is true for the copolymerization of butadiene with styrene, whereas the values of the chain transfer constant are larger than those for the homopolymerization of buta diene catalysed by Alfin.
By assuming the molecular weight of the resulting polymer to be controlled by the transfer of an active hydrogen in 1, 4-dienes the degrees of reactivity of 1, 4-dienes with Alfin catalyst were determined by measuring the amount of propylene evolved.
Furthermore, the values of activity of 1, 4-dienes were calculated according to the Streit wieser's method based on simple molecular orbital theory.
It was concluded that a suitable moderator is the one which does not react strongly with Alfin catalyst, does not retarded the re-initation of polymerization after hydrogen transfer and has the activity whose pK value is about 26-33.