High temperature, flame-retardant, and transparent epoxy thermosets prepared from an acetovanillone-based hydroxyl poly(ether sulfone) and commercial epoxy resins

A phosphinated biphenol, 6-(1-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl)ethyl)-6H-dibenzo[c,e] [1,2]oxaphosphinine 6-oxide (1), was synthesized from a sustainable phenol, acetovanillone. A methoxy-substituted poly(ether sulfone), methoxy-PES-1, was successfully prepared by the nucleophilic substitution of (1) and difluorodiphenyl sulfone in the presence of potassium carbonate. Another phosphinated biphenol, 6-((4-hydroxy-3-methoxyphenyl)(4-hydroxyphenyl)methyl)-6H-dibenzo[c,e] [1,2]oxaphosphinine 6-oxide (2), was prepared from another sustainable phenol, vanillin. However, the preparation of the methoxy-substituted poly(ether sulfone) based on biphenol (2) is not successful due to the biphenol (2) being unstable in an alkaline condition. After demethylation of the methoxy-PES-1, a phenolic hydroxyl poly(ether sulfone), hydroxyl-PES-1, was obtained. The phenolic hydroxyl linkages of the hydroxyl-PES-1 act as reacting sites for the epoxy resins. High-performance, bendable, flame retardant, and unexpectedly transparent cured epoxy film can be achieved through the curing of hydroxyl-PES-1 with commercially-available epoxy resins.

240