Sulfone-bridged difuran polyesters

Oxidation of 5,5 '-sulfanediyldi(furan-2-carboxylic acid) in acetic acid with aqueous hydrogen peroxide was used to prepare a new dicarboxylic monomer with a central sulfone group flanked by two biomass-derived furan rings. The new sulfone monomer was reacted with ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol to prepare new homopolyesters. Of these diols, 1,5-pentanediol yielded polyester with the most favorable properties in terms of processability and appearance. It could also be recycled back into the starting monomer under mild conditions. Using 1,5-pentanediol, a copolyester containing a 1:1 mixture of sulfone and sulfide difuran units was also prepared for testing alongside the corresponding sulfone difuran homopolyester. From measurements carried out on film samples of these two new materials, it was found that the new sulfone monomer will lead to polyester materials with high glass transition temperatures, high tensile stiffnesses, and low O2 permeability. The nature of the side reactions related to the difuran sulfone moiety under high temperatures remained unclear, as thermogravimetric analysis indicated relatively good stability characteristics and the monomer appeared relatively stable even at high temperatures.