The Constitution of Butadiene Polymers. Communication No. 259 on Macromolecular Compounds. Communication No. 5o on Rubber

Abstract

Abstract When butadiene is polymerized, the resulting polymers are composed of macro-molecules which have branched structures. The actual linking of butadiene molecules to form polymers may proceed in different ways. Not only can linking take place at the 1,4-position (see Formula 1) or at the 1,2-position (see Formula 2), but an addition reaction can take place at the 1,2- and 1,4-positions (see Formulas 3a and 3b). As a result, extensively branched molecules are formed, for the lateral chains unite by means of their double bonds with more butadiene molecules, either in the 1,2-position or in the 1,4-position. Finally it is not impossible that, to at least a small extent, two butadiene molecules unite directly, in accordance with a diene synthesis, to form vinylcyclohexene, which, after activation of its double bonds, reacts with more butadiene molecules in the 1,2-position or in the 1,4-position. Technically, butadiene was at first polymerized with sodium (Bunas with numerical designations), but today it is polymerized chiefly in the emulsified form5, and this process is used also to prepare mixed polymers (Bunas with letter designations). In the investigation to be described, this latter group of Buna rubbers was not studied, because in most cases they are insoluble, or swell only to a limited extent, and therefore it is impossible to determine either the size or the shape of their macromolecules, as can be done with soluble sodium polymers and emulsion polymers.