Hierarchical Structure of Poly(Ε-Caprolactone) Crystals on its Copolymer Poly(L-Lactide-Co-Ε-Caprolactone) Fibers

Abstract

In crystallization, heterogeneous structures of copolymers are used to form a hierarchical structure of two different polymers, this typically occurs on the surface of block copolymers or blended polymer. While hierarchical structures in block copolymer fibers are well-established and widely utilized, achieving a regular hierarchical structure on random copolymer fibers is both meaningful and challenging. Here, we present a case of forming a hierarchical structure on the surface of the random copolymer poly(L-lactide-co-caprolactone)（PLCL）fibers. The (ε-caprolactone)(CL) polymer chain segments of the random copolymer are released on the surface of the modified copolymer fiber using sodium hydroxide. Subsequently, poly(ε-caprolactone)(PCL) forms a shish kebab-like crystalline structure under the guidance of the CL segments. Here, CL segments act as crystalline precursors to induce the formation of heterogeneous PLCL/PCL shish kebab structures. The variation of CL segments on the fiber changes with modification time, leading to the formation of crystalline lamellae of different sizes, which had been confirmed by characterization techniques such as scanning electron microscope (SEM), 1H NMR, X-ray photoelectron spectra (XPS), differential scanning calorimetry (DSC), etc. The implementation of this heterogeneous structure provides possibilities for the implementation of hierarchical structure in random copolymers.

Keywords: shish-kebab structure, PCL, PLCL, CL segment, surface modification