'Fraid Not.
The breakdown of plastic is a complex process, but here is a simple way to describe it that will help make it clear why it's irreversible:
To make plastic, you put several different chemicals together, along with other factors like heat and/or pressure, binding the chemicals to one another. When you're through, it seems as if you have made a permanent new substance.
What you cannot see when plastic is new is that the binding together is only temporary. The separate chemical components of the plastic are attempting to break back down into their individual identities from the very beginning. As time goes on, they break down more and more.
If there was a way to keep plastic from breaking down, Hollywood would be extremely interested to know of it. One of the huge problems in the film business is breakdown of films being stored; many classic films have been lost forever to breakdown. Movie studios protect films by keeping them in dark, dry, cold environments, to slow the process as much as is possible, but even the best storage conditions only delay the inevitable - though a great deal of time can be gained through proper storage.
You can try keeping plastic in a low-humidity, cool environment and away from light if you're interested in preserving it as long as possible.
