What happens to polymers under high pressure?

What happens when you have polymers under high pressure? My very sketchy thoughts of polymers are that they can be thought of tangles of carbon chains surrounded by hydrogen, but that some polymers like polyethylene can be ordered or "crystalline". So it seems like there could be phase transitions, or if the pressure was high enough the polymer would have to change it structure or if in a tangled structure perhaps break links and form new links making a new polymer?


Edit: Very high pressures like those used in diamond anvil cell experiments.


