From the loctite website:
Threadlockers are a single component anaerobic adhesive comprised of unique liquid resins that harden (or cure) to a durable solid when exposed to metal ions in the absence of air. The anaerobic cure mechanism allows the adhesive to flow and evenly settle to lock and seal threaded fasteners without curing permanently. Any excess threadlocker will remain liquid, and is easily wiped away from the assembly.
I took a workshop on loctite adhesives once. Note that Loctite makes many types of adhesives, not just the threadlockers we normally identify them with. One thing they emphasized in the training is that anaerobic adhesives are not compatible with most plastics, and polycarbonate is especially vulnerable. An interesting fact is that the red plastic bottles they use for most of their threadlockers is microscopically vapor porous, like an eggshell or goretex. This prevents the threadlocker from curing in the bottle.
Loctite does make a threadlocker specifically for plastic parts and plastic fasteners. It’s Loctite 425. This is cyanoacrylate (superglue) based, rather than anaerobic. Cyanoacrylates cure in the presence of water vapor. So this stuff comes in a bottle designed to keep air out, rather than allowing it in.
The workshop was really cool. They had all sorts of fun little demos that showed how the various products worked. One of these was a demo of the green product used to lock slip fit cylindrical parts. They gave us a collar and a piece of shaft. You put a drop of the adhesive on the joint and immediately started moving it back and forth, preventing the polymeric bonds from forming. As long as you kept moving the joint, it stayed liquid. If you stopped for a second, the adhesive would harden instantly.