It has been shown that the extreme enhancement of strain at break for blends polycarbonate/poly(ethylene terephthalate) blends is due to the corresponding structural changes of the indicated blends, which are characterized by their structure fractal dimension variation. The blends deformability rise can be achieved by enhancement of either Flory-Huggins interaction parameter, or shear strength of their autohesional contact. The transparence threshold of macromolecular coils achievement results in sharp reduction of strain at break, i.e. its decrease practically up to zero.