There were a lot of questions in there.
I'll start by saying that in developing new materials or new plastics there's often a goal in mind. You want to make a material stronger so that you need less of it to reduce the weight of your vehicle, for example. There's a lot of research in aerospace in trying to make lighter planes, or in safer batteries by making polymers so that you can have polymer electrolytes. There are a lot of examples of developing new materials, but yes, unfortunately, even the smallest change in the polymer structure can change not only its mechanical properties or its application but its toxicology and how easily it can be broken down.
When I think of recycling, we wouldn't talk about recycling paper and metal in the same sentence. Some of these polymers can be completely different, and they have to be handled completely differently. The addition of one extra carbon can make it water soluble or such that it needs to be heated to a hundred degrees hotter to be handled. The small changes can have huge implications.
In terms of where the toxicology comes from, it can come from a lot of different places. It could come from, for example, the catalysts or unreacted monomers in manufacturing if there are impurities left over, or it could be from the actual polymer as it starts to degrade, is being worn down and enters our environment as a microplastic or other things like that. The toxicology can come from different aspects.