Mix sodium bicarbonate in the chloroprene?
As a teen, I did it with epoxy, it works. Heat decomposes the bicarbonate which emits carbon dioxide that keeps further heat at large. Within limits as usual.
Anyway, heating chloroprene or any chlorinated organics near one's nose is a bad idea. The fumes are toxic and repellent for real.
The bicarbonate idea was already known when I was young. (Neolithic had already begun).