Yea, it depends on what you are going after. If this is going to be a mast that is used in storms, where it is a tall structure compared to other surrounding structures (or if it has electronics mounting on it) how are you going to ground (or electrical bond) the sections and does it need earth grounding?
And like I said, I am a designer so I tend to think of any/all possible issues, even if the question is no problem.
As for the material, you might look for anything made out of delrin. We used that a lot in moving/sliding applications as the material has an oil based property more so than standard plastic.
On another note look for telescoping masts, telescoping poles and telescoping antennas for ideas. I am amateur radio and they are used a lot for temp antennas. But, they are starting to be made more out of composite materials to make them lighter and quicker to setup at emergency locations.