Evaluation of molecular weight of original epoxy acrylates in UV-cured resins by pyrolysis-gas chromatography in the presence of organic alkali

Molecular weight of bisphenol A type epoxy acrylate (BEA) prepolymer in UV-cured resins was estimated by pyrolysis-gas chromatography (Py-GC) in the presence of organic alkali, tetramethylammonium hydroxide (TMAH). The pyrogram of the UV-cured resins mainly consisted of various methyl ethers containing a bisphenol A unit along with methyl acrylate (MA) and some products from 2-hydroxypropyl moieties. In addition, on the pyrograms of the UV-cured resins prepared from oligomeric BEA having larger molecular weight, methyl ethers containing two bisphenol A units were also observed. The relative yields of the methyl ethers containing one or two bisphenol A units, which should be formed through pyrolysis and methylation at ether and/or ester linkages in the cured resins, considerably varied depending on the molecular weight of the original BEA. A series of UV-cured resins consisting of monomeric and oligomeric BEA with various molecular weights were measured to ascertain the relationships between the molecular weights of the original BEA and the relative yields of the specific products during the reactive pyrolysis with TMAH. The average molecular weights of the BEA moieties in the UV-cured resins estimated by this approach showed good agreements with those of the original prepolymers even for the multi-component cured resins.