(EN) A cross-linkable polymeric casting composition including an effective amount of a divinyl ester monomer of a bicyclic or polycyclic compound, and optionally a minor amount of a di- or polythio compound. The specification and claims include allylic ethers within the definition of 'divinyl ester', for example bisphenol fluorene diglycidyl allylic ether and bisphenol S diallyl ether.