Degradation of Pmma must be very slow, since windows are made of it, exposed to sunlight and weather, and they keep transparent for decades. Pc is more sensitive to scratches. One of them is very sensitive to solvents, which crack the surface.
Light, sure. Natural rubber is in addition very sensitive to ozone, even in tiny concentration as an atmospheric pollutant. I've seen some rubber rings degrade in few years, others stay sound for longer; possibly a matter of stabilizers, vulcanization or copolymers and blends. Tyres are loaded with carbon black, one goal is to protect against UV, they (all?) contain some natural rubber and don't degrade quickly.
Only as a feeling, I'd suppose that repeated deformations do little to natural rubber, because it's the one rubber that goes back to its original shape, and quickly. No synthetic rubber is as good for that. It would be easy to try.
Protective silicone: try it. Difficulties:
- Even silicone can't stretch as much as natural rubber
- Adhesion uses to be poor
- Silicone rubber is permeable too, and deformation won't help.