I've got a 7 year old house and the windows have this plastic molding
around each window pane ( not sure if this is called window
sashes?? ). Since this house is in texas, the hot sun beats on them
for months each year and they are starting to get brittle and small
pieces are starting to chip off leaving small holes.

What are these correctly called and can they be replaced? Is there a
material that will prevent cracking or chipping ?