PVC plastic, which is the same plastic that is used for PVC pipe, is the trim that is used on virtually every modern synthetic window installation. It is incredibly durable, and unlike organic window trim like wood, PVC is unaffected by moisture or humidity, never needs to be stripped and renewed and resists dings and dents. Cleaning can also be done with every day common home cleaning agents that virtually everyone will have around the house.
Wipe off the PVC window trim with a damp rag.
Mix up a bucket of water with a cap full of dish washing detergent added. Add another cap full of detergent if the window trim is particularly greasy or oily.
Soak your scrubbing sponge into the dishwashing mix. Wring it out. Using the abrasive side, gently scrub the trim with the sponge.
Wipe off the trim with a damp rag dipped in the fresh water bucket and inspect the trim. If there are any scuff marks, sprinkle on some regular kitchen cleanser.
Scrub gently over the top of the kitchen cleanser with the abrasive side of the sponge. Rinse thoroughly by dipping your rag into the fresh water bucket and removing all traces of cleanser and soap. Allow it to air dry.
For extremely difficult stains, you can also use a little acetone and some OO rated steel wool to scrub them out. Wash afterward with your dish soap mix. Wipe and allow it to air dry.
If acetone is used, make sure the room is well-ventilated and rubber gloves are worn to protect your hands.