Briefly, there are a number of problems.
1) Wind forces would rip it apart.
2) Balloons leak.
3) To float even, say, an empty two-liter bottle requires a
balloon larger than the bottle. A full one (imagining
something actually trying to climb the pipe) would take a
much larger one, even at ground level.
4) Since the atmosphere thins as you rise in altitude,
balloons don't float as well higher up.
5) Since there's wind, even if it didn't get ripped
apart, it would probably end up at a 45-degree angle,
and subjected to enormous forces (imagine attaching one
end of a soda straw to the ground and the other to a balloon).
6) a 100-km long pipe with the relative dimensions and
structural strength of a soda straw, or even ten end-to-end,
would be about 100 feet in diameter.
Incidentally, nanotechnology will solve many of these
problems by:
1) making much stronger materials possible, getting rid of the
problems of wind shear and large diameter (which creates
wind resistance)
2) allowing us to make lots (billions) of tiny
(buckyball-sized) balloons instead of clunky big ones --
and buckyballs don't leak
3) allowing the surfaces to react to the wind direction
using AI and tiny actuators
Sorry not to be more rigorous, but I'm packing for a trip
and it already doesn't look like I'm getting any sleep.
Kennita