Why do vinyl raincoats become brittle as they get old, even if they are not exposed to air or to any pollutants

The substances made from polyvinyls are generally brittle and hard. This property prevails because the polymer strands present in the polyvinyls form a very regular and well-organized packing composition in the solid-state. The Van der Waals associations between the strands make the substance brittle. To make the substance soft and suitable to use as a raincoat, the incorporation of small molecules is done within the molten polymer before the hardening of the plastic.

These polymer strands act as plasticizers and prevent the strands of polymer from forming a hard and brittle conformation.

answer; i believe that the correct answer is (a); a large rock being weathered by wind and rain;