American-made acrylic does NOT yellow in the sunlight. Witness the protective canopies and bubbles in the WWII 

Plexiglas is a trade name acrylic (extruded or cast medium grade acrylic sheets, rods, tubes) , PVC (type 1 clear, also i the acrylic family), PET (polyester, soad bottle material). Butyrate (mostly extruded tubing), and Polycarbonate (Lexan, Hyloid) are all clear plastic resins with wide a range of properties. My bad on classifying plexi as a polycarb, Plexi is mainly used as a glass replacement or for weight savings. Duh! the hammer isn’t even necessary, just drop both from waist level. Or try to drill Acrylic sheet.

ANYWHO! As mentioned, Acrylic aquaria built using quality float cast plastics should give you decades of service if properly cared for (not scratched and gouged). A yellowing can happen, sure if in direct sunlight, overheated, oe bombarded by UV. I think most is USDA approved too (could be wrong, let me know) which means the will not absorb, hold or leach toxic chemicals/materials. 1/2″ Lexan will stop a .45 cal.