bathtub surface sealant?
 

I am sure the answer is on the internet, but I have been unable to
come up with the correct keyword combination to find it.

The problem is a whirlpool bathtub in the bathroom. It functions well
enough, but the surface seems to attract dirt and needs a scrubbing
almost after every use. It is an acrylic/plastic type of surface, not
enamel or porcelain.

I was wondering if there is some sort of product (like a silicon based
sealant/protectant or something) that could be applied to the surface
and applied after a good cleaning so that it would be a lot more
resistant to surface 'scum' buildup?

TIA for any info or clues.