Moisture Tolerance of Epoxy, Oxetane and Vinyl-Ether Cationic Photoresins

Water can act as a proton carrier, nucleophile, chain-transfer agent, hydrolysis reactant, plasticiser or separate phase in cationic photoresins. Its effect is therefore not represented adequately by one humidity value or by the statement that moisture inhibits cure. Epoxy, oxetane and vinyl-ether systems differ in monomer structure, basicity, miscibility, propagation route and network development, while formulation components change the amount and state of water that reaches the reactive species. This review defines a comparative moisture-tolerance qualification architecture. It requires measurement of resin water content and phase state before exposure, chemistry-specific conversion during irradiation, post-irradiation dark evolution, thermal post-cure where used, and remeasurement after controlled conditioning or storage. Primary evidence covers all three monomer families, real-time water and monomer monitoring, cycloaliphatic-epoxy models, oxetane/epoxide combinations, dark cure and hybrid-network consequences. The evidence shows that water can accelerate, retard or redirect parts of the reaction depending on chemistry and state. It supports formulation-specific tolerance boundaries, not a universal water limit, humidity limit, drying instruction, monomer-family ranking, exposure compensation or shelf-life claim.