Nucleobase-monofunctionalized supramolecular poly(l-lactide): controlled synthesis, competitive crystallization, and structural organization

Abstract

End-functionalization of oligomers with multiple H-bonding units is a feasible method to prepare supramolecular polymers. Competitive crystallization of H-bonding units and oligomeric blocks can drive supramolecular polymers to form long-range ordered structures. Herein, we report the controlled synthesis, competitive crystallization kinetics, and crystallization-driven structural organization of thymine-monofunctionalized supramolecular poly(L-lactide) (PLLA-Thy). PLLA-Thy having a well-defined end-functionality and controlled molecular weight was synthesized by ring-opening polymerization using hydroxyl-functionalized thymine as the initiator. PLLA-Thy exhibits the double-crystalline nature, in which the PLLA block and the thymine terminal have a similar crystallization temperature (T_c) and melting point (T_m). The crystallizability of the thymine unit was depressed in PLLA-Thy with a long PLLA block. The thymine terminal and PLLA block revealed the competitive and coincident crystallization kinetics in PLLA-Thy with a medium thymine fraction, depending on T_c. Prompt crystallization of the thymine unit drove the lamellar organization of PLLA-Thy in a long range; the subsequent crystallization of the PLLA block segregated between thymine layers depressed the regularity of the lamellar ordering of PLLA-Thy. This work provides important insights into the multi-step crystallization and crystallization-induced structural organization of semicrystalline supramolecular polymers.