STUDIES IN THE PHOTO-DIMERIZATION OF THE DIGLYCIDYL ETHER OF 4,4'-DIHYDROXYCHALCONE

In order to elucidate the reaction mechanism involved in the photocrosslinking of epoxide resins containing the 4,4′‐dioxychalcone functional group as part of the polymer backbone, the behavior of the monomeric model compound, namely, the digylcidyl ether of 4,4′‐dihydroxychalcone, when subjected to UV irradiation has been studied in some detail. The initial photochemical reaction is trans‐cis isomerization to a photostationary state, the trans/cis ratios in this state being wavelength dependent. This is followed by a slow dimerization to dimers of the truxillic and truxinic type, the products being mainly formed from the trans isomer under our conditions of irradiation (λ = 350 nm). GPC studies on the irradiated products also reveal the formation of low molecular weight oligomers. Irradiation in the solid phase resulted in the conversion of 37% of the reacted monomer into polymer, whereas irradiation in the solution phase led to 23% of the reacted monomer being converted into low molecular weight polymer. A slow depolymerization of the dimer into the monomeric chalcone is also believed to occur on irradiation at 350 nm. Copyright © 1979 John Wiley & Sons, Inc.