Koppers' rhymes with:
copper's, coppers, koppers, boppers, chopper's, choppers, copper's, coppers, droppers, hopper's, hoppers, koppers, loppers, poppers, shopper's, shoppers, shoppers', stoppers, toppers, whoppers
Koppers' sounds like:
kasparek, kasperek, kasperski, kasprowicz, kasprzak, kasprzyk, keepers, kippers, koperski, koppers, koprowski, kosberg, kovarik, kozberg, kuberski, kubrick, kubrick's, kuipers, kupres