  In this paper we obtain the [60,30,12], [64,32,12], [68,34,12], [72,36,12]
self-dual codes as tailbitting convolutional codes with the smallest constraint
length K=9. In this construction one information bit is modulo two added to the
one of the encoder outputs and the first row in the quasi-cyclic generator
matrix is replaced by the obtained row. The pure quasi-cyclic construction with
K=10 is also available for [68,34,12] and [72,36,12] codes. The new [72,36,12]
singly even self-dual code with parameters Beta=483 Gamma=0 was obtained.
