High Molecular Weight Soybean Oil-based Polyesters through Carboxyl-ester Transesterification

Soybean oil-based diols (SOD) can be synthesized from soybean oil and polymerized with diacids to give soybean oil-based polyesters. However, the conventional esterification and transesterification mechanisms of polycondensation are incapable of obtaining high molecular weight (HMW) soybean oil-based polyesters due to the kinetic deviation of diol/diacid unit ratio from 1 : 1, which is required for producing HMW polyesters. Here we introduce a novel carboxyl-ester transesterification (CET) mechanism to synthesize HMW soybean oil-based polyesters through melt polycondensation. Using excess diacids to esterify with SOD, a carboxyl-terminated prepolymer was first afforded. Then the excess diacids were regenerated via CET and removed through sublimation, thus dynamically approaching the stoichiometric condition of the diol/diacid unit, through which a series of HMW soybean oil-based polyesters with viscosity-average molecular weights up to 123 kDa were obtained. The resultant polyesters exhibit good thermal stability and high transparency, and their adhesive performances are comparable to those of commercial pressure-sensitive adhesives. Furthermore, antibacterial soybean oil-based polyesters were achieved via thiol-ene "click" reaction of the alkene groups in the aliphatic side chain of polyesters with a thiolated quaternary ammonium salt.