A polarizing filter has two main uses; to reduce surface reflections and to darken the sky. This happens because the polarized components of the sky are filtered out, causing it to look much darker and more dramatic. This effect can be advantageous in landscape photography.
Unfortunately, most polarizing filters don’t work in IR light and only affect the visible light spectrum. Some optical glass companies sell special infrared polarizing filters, they are quite pricy but do work wonderfully in IR light.
Before spending the big bucks for a dedicated IR polarizing it may be a good idea to test the polarizing filters you already own, chances are it may still provide adequate performance in IR.