I'm looking for suggestions how to get a polyimide ribbon sheet embedded into PEEK. The final structure is a hollow cylinder 5" long with OD 0.5" and ID 0.25".

The ribbon needs to run along the length of the cylinder inside the PEEK. There is no particular tolerance needed for the sheet to be in position inside the PEEK, only that it not be shredded into pieces. I've checked that the polyimide will stay intact if it is dipped into molten PEEK, but yes that is not the same as it surviving in high-velocity, high-pressure molten fluid.

Seems like it will be tricky to hold the sheet in place....

I'm thinking another possibility could be to make one cylinder 0.35" OD and then glue the polyimide to the OD of that and then overmold PEEK on top of that. I see online that PEEK can overmold onto PAEK and the PEEK bonds to the PEAK. I would assume that the PEEK would not bond well to the polyimide, i.e. that there would be an internal defect but that the rest of the assembly would be solid.

Maybe there are other ways of construction?