The syndiotaetic 1

2-polybutadiene-1，4-polybutadiene copolymer is crystalline with a m.p. of 205—-210℃．independent of the content of 1

2-unit．It is considered that the copolymer is block in nature．The DSC peak temperatures (Tp) for thermo-oxidation of a low 1

2-content (12一 20％) sample and a high one(95一100％) are 185 and 200一240℃，respectively．It is believed that the double bond in side group is more stable than that in the main chain．The difference in stability

between the two kinds of double bond can be explained by the facts that：1) the inner．double bond has four a-hydrogens，but the outer one has only one；2) the

block of 1

2-unit is crystaUine below 203℃，whereas that of 1

4-unit is amorphOUS even at room temperature．The activation energy

exothennal effect of thermo-oxidation for high 1

2-oontent polybutadiene of various conversion is also described．