I purchased some Bitcoin on Coinbase with the intent of sending it to Poloniex. I accidentally sent my Bitcoin to my Bitcoin Cash address on Poloniex. Is it possible to retrieve the Bitcoin or is it gone?
It is going to be very difficult for you to get those bitcoins back, especially since you don't own the private keys to the wallet that you sent to. My guess is that you are out of luck. i hope it was not a great quantity.
Each wallet on poloniex has a warning on it stating to only send that currency (e.g only send bitcoin cash to this wallet) or you risk losing your coins.