Stepwise and catalytic polymerization of butadiene by organosodium reagents

Abstract

For many years the polymerizations of butadiene by organosodium reagents in this laboratory have fallen into two extreme categories: one, long known and well defined in the literature,' is a relatively slow, stepwise growth, primarily in a 1,2-manner; the other is a rapid catalytic process which cannot be interrupted. The latter is best illustrated by the combination2 of allylsodium, sodium isopropoxide, and sodium chloride which induces primarily 1,4-polymerization, mostly to a trans form; possibly because a simultaneous change about the double bond occurs, organosodium compounds being active agents for isomerization, even at room temperature.3These two types can be distinguished by comparing polymerizations with additions to 1,l-diphenylethylene, a prototype for that kind of reaction; data for that purpose are a t hand from previous publications. Figure 1 shows a plot of the relative yields obtained in additions4+ against the yields obtained in polymerizations, each to the basis of amylsodium as 1.The stepwise processes lie on the upper line; the catalytic one^?^^^^ are on a lower line and best a t the lower right. Amylpotassiumx lies between the two lines but, all things considered, (i.e., yield, viscosity, an infrared absorption) might be regarded as in the catalytic area. The cation, being different from those in the reactions to which this is compared, probably affects that case, because potassium and sodium reagents do not always behave alike, even in a simple m e t a l a t i~n .~~~ The viscosities for the polybutadienes on the upper line are low and of the same order of magnitude (0.1 to 0.2). That result could be expected, as, after one or two dienes have added, the growing ends should be identical, and thereafter the chain lengths should become similar.The catalytic processes are distinguished for their failure to follow that rule. In some way the diene molecules are concentrated a t the growing end, so that they join the chain with unusual rapidity. A high concentration must come, logically, from a preferred or orderly adsorption, as contrasted with random adsorption for stepwise polymerization. 233Both axes are graded logarithmically.

The preparation and properties of polybutadiene (jumping rubber)

“…The name, alfin, was taken from the fact that an alcohol and an olefin are involved in the preparation of the reagent. The alfin catalyst is believed (5,6) to adsorb and orient the monomer prior to the chain-growth process. Surface effects presumably influence the stereochemistry (4), and the poly-mer consists mainly of trims-1,4 repeating units.…”