"An inflatable chair from 1969 has gone rigid, while a PVC minidress is now so sticky that it must be kept behind glass...The problem is that plastic is not as stable as many thought, and is now decaying. 'It's something that museums all over the world are trying to find a solution to,' says head conservator Sandra Smith."The real problem that I see is that the solutions are not very acceptable. You are pretty much stuck with keeping the items in a dark, oxygen- and moisture-free environment, all of which prevents anyone from viewing the objects.
These objects were born staring at a premature death. They were made from resins that were inadequately stabilized for the long-term (meaning centuries). If a plastic chair or dress lasted for 10 years of use, that would have been considered acceptable in most situations, but art conservationists have a much longer viewpoint, and so artists need to adapt too. Just as there is artist grade paper, pencils, paints etc., artists need to start working with more highly stabilized plastics if they wish for their art to last.
While it is tempting to comment about how "natural materials" have been used in the past to create long-lasting art and that plastics should not be used to enduring creations, this view is a classic example of "Survivorship Bias". The paintings, sculptures and other objects that we have kept from over the centuries are ones that, probably more from luck then intelligent foresight, have survived. Early oil paintings for instance, are seldom found as no one knew initially how to make them durable. That knowledge has since been discovered and we now have oil paintings from the centuries ago. That same path will be repeated with plastics. As artists become aware that they need special materials (and possibly processing techniques) to make a truly durable creation, they will adapt rather than create objects from inherently weak materials.