DI Electric Constant

Here is one source, but unfortunately none of the common plastics listed has a dielectric constant that high. Maybe something more exotic?

Tedlar is high.

3M's Epsilam 10 is higher still.

Have you looked anywhere?

And, it's dielectric, not DI electric.

It depends on the conditions...these are the highest I could find, neophrene might work, but that is rubber, all other plastics seem to fall in the 2-3 range...8.5 at 1 hz, 7.4 at 1 mghz..

You have not made clear what you mean by plastic. Some are "thermosetting". Bakelite is described as a plastic and has various forms which span the permittivity range you want. Silicone rubber sealing etc compounds (Silastic) come in many forms, mixed with inorganic powder insulators. They are more flexible when set than bakelite. Try Dow Corning company. I guess a suitable mix may cover the range you want.

I want a thermoplastic and must be Rohs complains

It would save a lot of time and guesswork if all the constraints to the problem were available and described in the original post, next time.

Otherwise it looks as though a problem is being found for every solution.

What is the application? Yes it matters.

this is for electrical applicatiob for RF waves

Noted you want thermoplastic for RF.

The dielectric constant you want is very high for thermoplastics, Also you want a specific range. I think you will only get it by mixing a suitable plastic with a high "k" inorganic filler - a specialist material. No easy solution.

I suggest a search of Globalspec for "thermoplastic" and an enquiry to companies found - I tried it and noted Dupont and a company called SABIC which specialises in compounds.

Over to you.... you have given no info on the purpose (cable/tube/dielectric separator), temperature, stability, flexibility etc requirements. If you want a solution, you will have to write a spec, covering all requirements, and ask suppliers for their suggestions to meet it.

It will pay to identify the properties in order of importance to your use, so it is clear which you can compromise about.

...circuit board, filter components, transmission lines....???