  We have computed new stellar evolution models that include the effects of
rotation and magnetic torques under different hypothesis. The goal is to test
if a single star can sustain in the envelope the rotational velocities needed
for the magneto hydrodynamical (MHD) simulations to shape bipolar Planetary
Nebulae (PNe) when the high mass-loss rates take place. Stellar evolution
models with main sequence masses of 2.5 and 5 Mo, and initial rotational
velocities of 250 km/s have been followed all the way to the PNe formation
phase. We find that stellar cores have to be spun down using magnetic torques
in order to reproduce the rotation rates observed for white dwarfs. During the
asymptotic giant branch phase and beyond, the magnetic braking of the core has
a practically null effect in increasing the rotational velocity of the envelope
since the stellar angular momentum is removed efficiently by the wind. We have,
as well, tested best possible case scenarios in rather non-physical contexts to
give enough angular momentum to the envelope. We find that we cannot get the
envelope of a single star rotating at the speeds needed by the MHD simulations
to form bipolar PNe. We conclude that single stellar rotators are unlikely to
be the progenitors of bipolar PNe under the current MHD model paradigm.
