The parameters

K and a of [η] = KMa/w

for 1

2-polybutadienes at 30℃+ in toluene

has been determined. It has been found that the values of a of samples with various 1

2-unit contents are basically the same

but the values of K decrease with increase in 1

2-unit content.The relation between T0 and σ of the samples has been found to be Tg=A(σ-b)

in which A and b are 174 and 0.68

respectivly

indicating the internal rotation of the molecular chain is hindered by 1

2-unit.It has shown that less 1

2-unit content corresponds to lower poltential barrier of internal rotation and hence to lower energy of rotational isomerization.