what would you use to bond PR to itself? CA or MEK or... ?
Polyester resin will form a chemical bond with partially cured PR
if the surface is still tacky. That is how thick fiberglass layup is done. Although each layer sets up before the next is laid, it all fuses together into one solid crystal.
Once fully cured (dry surface), however, freshly applied PR will not make a chemical bond - only a mechanical bond. For good adhesion, you need to lightly sand the surface (to give it some "tooth"), clean it with acetone, and then add resin.
If you're asking what glue to use for PR segmentation, I'd go with CA (MEK works as an acrylic cohesive, but not on PR). If you want to do a multi-layer casting, pour each layer after the previous one has set up, but before the surface hardens. IF you're overcasting a cured blank, scuff the surface first.
I hope that helps,
Eric