Self-assembly and amphiphilic behavior of poly(ester)-block-poly(amide) diblock copolymer based on biodegradable poly(butylene succinate) and poly(2-pyrrolidone)

In the present study, a novel poly(butylene succinate)-block-poly(2-pyrrolidone) (PBS-b-PA4) diblock copolymer was first designed and synthesized by condensing amino-terminal PBS and carboxyl-terminal PA4 at 100 °C under homogeneous conditions. The PBS-b-PA4 chemical structure was determined by combining nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) analysis, while the solid-state structure was investigated by wide-angle X-ray diffraction. In addition, the self-assembly behavior of the copolymer was studied by optical microscopy, NMR spectroscopy, and light scattering experiments using appropriate solvents. Both terminal groups of PBS-b-PA4 were well characterized, and the average molecular weight of PBS-b-PA4 was consistent with the sum of the precursors. The diffraction patterns also confirmed the presence of precursors. Micelle-like colloidal particles with an amide segment core and an ester segment corona were eventually observed in chloroform. Additionally, it was revealed that PBS-b-PA4 formed a birefringent and fluid liquid crystalline phase in 1,1,2,2-tetrachloroethane. Thus, the emulsifying property was demonstrated in an immiscible two-liquid solution, indicating that the PBS-b-PA4 diblock copolymer is effective as an emulsifier at a comparable concentration of 1 g L-1. Furthermore, the amphiphilic behavior of PBS-b-PA4 was attributed to the varying solubilities between the ester and amide segments. Thus, PBS-b-PA4 could be a promising candidate as a compatibilizer for PBS/PA4 resin binary blends.