Is polar a noun

No, polar is not a noun, it is an adjective. Here are some examples:

• Polar bear: polar is describing the type of bear
• Polar ice cap: polar is describing the type of ice cap
• Polar easterlies (type of wind): polar is describing the area that the winds blow

However, in one case, polar maybe used as a noun, to mean the straight line (polar line) joining the points at which tangents from a fixed point intersect a conic section.