Synthesis of Multiblock Copolymer Composed of Biodegradable Poly(butylene succinate) and Poly(2-pyrrolidone): Impact of Each Block Length on the Mechanical Properties

A series of multiblock copolymers comprising a systematic combination of biomass-originated and biodegradable poly(butylene succinate) (PBS) and poly(2-pyrrolidone) (PA4) units is synthesized with various mean degrees of polymerization (mDP) of each unit. Despite the inherent immiscibility of PBS and PA4, multiblock structure allows to mix the two components in the solution-cast films from solution. The mechanical properties of the cast films are highly dependent on the mDP of each unit, as demonstrated by tensile tests. The film of the copolymer with the lowest mDP of each unit (PBS: 17, PA4: 10) is transparent and exhibits extremely high elongation at break (> 400%) and high tensile stress (39.5 MPa) with strain hardening. The films with 50% or higher crystallinity are brittle and opaque, while a decrease in crystallinity can result in higher elongation, as revealed by wide-angle X-ray diffraction measurements.