Stepwise Crystallization and Induced Microphase Separation in Nucleobase-Monofunctionalized Supramolecular Poly(ε-caprolactone)

End functionalization of homopolymers by noncovalent binding units is a straightforward approach to prepare supramolecular polymers with a broad application scope as stimuli-responsive functional materials. Crystallization and microphase separation of end groups and polymer blocks can lead to the formation of short- and long-range ordered structures in end-functionalized supramolecular polymers. Herein, we report the controlled synthesis, stepwise crystallization kinetics, and crystallization-induced microphase separation and structural evolution of a novel end-functionalized supramolecular polymer, thymine-monofunctionalized poly(ε-caprolactone) (PCL-Thy). PCL-Thy with high end functionality and adjustable composition was synthesized by ring-opening polymerization using hydroxyl-functionalized thymine as the initiator. PCL-Thy showed a double-crystalline nature; its thymine units and PCL blocks crystallized and melted in a stepwise manner in the cooling and subsequent heating processes. The crystallization of thymine units from the melt resulted in an ordered and aligned thymine stack, which further drove the microphase separation and long-range lamellar organization of the PCL-Thy. The subsequent crystallization of PCL blocks occurred in a confined manner between the pre-existing thymine lamellae and slightly decreased the regularity of lamellar ordering. The PCL chains, which crystallized between the thymine lamellae, transformed from nonfolded to single-folded crystals upon increasing the PCL block length. This work offers important insights into crystallization-induced microphase separation and hierarchical ordering in double-crystalline supramolecular polymers.