Novel thermosets obtained by UV‐induced cationic copolymerization of DGEBA with an spirobislactone

The photocuring process of the diglycidyl ether of bisphenol A (DGEBA) with the bislactone 1,6‐dioxaspiro[4,4]nonane‐2,7‐dione (s(γ‐BL)) was studied. Triarylsulfonium hexafluoroantimonate was employed as photoinitiator. FTIR/ATR was used to study the evolution of epoxy, lactone, and intermediate spiroorthoester groups to identify the different reactions that take place during the photocuring process. Photo‐DSC and DSC were used to study the thermal evolution of the photocuring process and to assess the Tg of the fully cured material. Thermogravimetric analysis (TGA) was used to determine the thermal stability of the fully cured material. The thermomechanical properties of the materials were investigated using dynamic mechanical‐thermal analysis. Shrinkage undergone during photocuring and gelation was studied with TMA. A strong influence of the photocuring temperature on the photocuring process of the DGEBA‐ s(γ‐BL) system was observed. Differences in the reactivity of the different species were observed with respect to the thermally cured system using ytterbium triflate as cationic thermal initiator. As a consequence, photocured materials exhibited a superior thermal stability and lower flexibility.