Aminolysis of Poly(butylene succinate) via a Microwave-Assisted Technique: Tunable Molecular Weight and the Hansen Solubility Approach toward Green Solvent Fractionation

Poly(butylene succinate) (PBS) is a promising biopolymer due to its mechanical properties similar to those of polyolefins and biodegradability. This work aims to synthesize PBS with tunable size and functional groups by depolymerizing commercial PBS resin and employing a green microwave-assisted aminolysis with ethylenediamine (EDA). The PBS:EDA ratios ranging from 40:1 to 15:1 are investigated, and a functionalized oligomer (αPBS) with a controllable number-average molecular weight (M¯n) from 67,376 to 5088 g/mol is accomplished. Solvent fractionation utilizing various solvents facilitates the selective separation of oligomeric fractions according to Hansen solubility parameters, correlating the molecular polarity with solvent affinity. The solubility test of αPBS oligomers with various solvents, e.g., dichloromethane, tetrahydrofuran, toluene, cyclohexane, acetone, and ethyl acetate, is systematically studied. The αPBS oligomer at a ratio of 15:1 (αPBS15) improves solubility in mild solvents (i.e., acetone) with a high fraction of 24%. To explore the potential applications under the green process, the oligomeric fraction is used to encapsulate a natural active ingredient (curcumin) by a classical oil-in-water emulsion method using acetone as a solvent. The results demonstrate successful encapsulation of curcumin into the oligomeric fraction and good dispersion in the water phase. These findings demonstrate a compound selection strategy based on the solubility of various sizes of αPBS oligomers, which may be key in identifying the applications of PBS-based materials for industrial products and valued medical applications.