Branching in Butadiene Rubber

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Abstract
1. By studying the intrinsic viscosities of fractions in an “ideal” solvent, the degree of branching of potassium-butadiene polymers was determined. It was found that a specimen obtained at 0° was already markedly branched; increasing the temperature of polymerization (to 40–60°) led to the synthesis of highly-branched polymers, containing one branching site per several hundred monomer units. 2. On the basis of quantitative data on the branching of the polymers studied, the difference between the activation energies of the chain growth and branching reactions was calculated for the polymerization of butadiene in the presence of potassium. At the same time it was found that the increase in the degree of branching of the macromolecules with the increase in temperature in the gas phase polymerization of butadiene was determined not only by the mentioned difference in the activation energies, but also to a considerable extent by the temperature dependence of the solubility of the monomer in the polymer. 3. It was shown that for the investigated system, fractionation of the branched polymers by means of fractional precipitation from dilute solutions yields fractions which differ in molecular weight but not in the degree of branching. 4. It is shown that the relation between the intrinsic viscosities of polymers of a given molecular weight but of a different degree of branching, remains constant in the switch from a good solvent to an ideal solvent.

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