Templating the crystallization of semicrystalline block polymers: from double crystalline to pentacrystalline spherulites

Semicrystalline polymers with well-defined multiple crystallizable blocks provide opportunities to develop materials with hierarchical structures and customized properties, but they also pose challenges for understanding their crystallization and morphology. In this invited lecture, we present the crystallization from a miscible (or weakly segregated) melt of a pentablock quintopolymer composed of five potentially crystallizable and biocompatible blocks: polyethylene (PE), poly(ethylene oxide) (PEO), poly(ε-caprolactone) (PCL), poly(L-lactide) (PLLA), and polyglycolide (PGA). The composition had to be tuned to allow for the crystallization of all five blocks. Using Differential Scanning Calorimetry, synchrotron Fourier Transform Infrared Spectroscopy, synchrotron in situ Wide-angle and Small-angle X-Ray Scattering, Transmission Electron Microscopy, and Polarized Light Optical Microscopy, we demonstrate that upon cooling from the melt, all covalently linked blocks crystallize in a well-defined sequence: PGA > PLLA > PE > PCL > PEO. The first block to crystallize templates the predominant spherulitic structure. Thus, during crystallization, unprecedentedly well-developed pentacrystalline positive spherulites were produced templated by PGA. In the tetra, tri-, and di-block precursors, different spherulites are generated, composed of four, three, and two lamellar crystals within the templated spherulites. This unprecedented level of self-assembly reveals the potential of complex block polymers to design multifunctional crystalline materials.