Please click through to the source link above to read the entire discussion on creep. The question asked below is not the original question, but the reply is spot on.
What are the material properties (in polymers) that define the resistance to creep (e.g. Shor value or some other parameter)?
Creep rate data for polymers is hard to find, but some googling can get you some useful information. Because the test is hard to do (special equipment, long duration of test) and the data highly non-linear, I don’t think there has ever been a standard methodology to define creep resistance, even in metals. One thing to do is find the melt processing temperature for thermoplastics, and look for ones with higher values, along with higher room temperature ultimate strength, this will narrow the list for you somewhat. Similarly, the heat deflection temperatures (ASTM D648) will point you towards more creep resistant materials, generally.
You also need to figure out how long your clamp is expected to hold a load - this will bound the time limits of your creep data.
In the end, if it’s critical, you will need to pay somebody to do testing on your material, do the testing yourself, or ask the material vendors for data. Reinforcements (fibers) in the melt can help, especially if you can get the fibers to align with the tensile stress.