Stability of Butadiene

1. The most prominent polymerization of pure butadiene in the absence of peroxides is dimerization. This reaction is thermally activated, and does not appear to be catalyzed by peroxides or by steel surfaces. 2. Butadiene is also capable of independent polymerization to high-molecular-weight polymer, but in the absence of peroxides this reaction is insignificant compared to dimerization. The effect of temperature on the rates of each of these reactions has been determined. 3. In the presence of appreciable amounts of peroxides, polymerization to high-molecular-weight polymer becomes prominent, and is superimposed additively on the thermal dimerization reaction. 4. The addition of suitable antioxidant inhibits the formation of high-molecular-weight polymer, but has no appreciable effect on the rate of dimer formation. 5. The rate of high-molecular-weight polymerization is directly proportional to the square root of the concentration of peroxides (active oxygen). 6. Butadiene is readily peroxidized by air, but this peroxidation may be inhibited for a time by the presence of antioxidants. 7. The peroxides are not readily volatile, and tend to accumulate in the residue if the diene is evaporated or distilled away. Concentration beyond a certain point yields an unstable residue which may decompose with violence when heated. Precautions for distillation of such peroxidized material are given.