  We present nucleosynthesis predictions for massive (5-7 solar masses)
asymptotic giant branch (AGB) stars of solar metallicity where we delay the
onset of the superwind to pulsation periods of P =700-800 days. We found that
delaying the superwind in solar metallicity massive AGB stars results in a
larger production of s-process elements, something that would be also expected
at lower metallicities. These new models and the available observations show
that massive C-O core AGB stars in our Galaxy and in the Magellanic Clouds
experience considerable third dredge-up (TDU). Thus, if massive AGB stars at
the metallicities of the Globular Clusters (GCs) also experience deep TDU, then
these stars would not be good candidates to explain the abundance anomalies
observed in most GCs. However, more massive AGB stars (e.g., near the limit of
C-O core production) or super-AGB stars with O-Ne cores may not experience very
efficient TDU, producing the high He abundances needed to explain the multiple
populations observed in some GCs.
