All-Polylactones Nano-Objects Prepared by a One-Pot Ring-Opening Polymerization-Induced Self-Assembly Process

Ring-opening polymerization (ROP) has been acknowledged as an efficient approach to biodegradable polylactones. Herein, by a sequential ROP of d,l-lactic acid (D,L-LA) and l-lactic acid(L-LA) monomers in toluene, we reported a ROP-induced self-assembly (ROPISA) process. The poly(d, l-lactic acid)-b-poly(l-lactic acid) (PDLLA-b-PLLA)-based all-polylactones nano-objects were prepared in a one-pot manner. The crystalline PLLA served as a core-forming block, and amorphous PDLLA acted as a stabilizer block. The morphologies of the generated nano-objects included spheres and platelets by varying the polymerization parameters. Uniquely, the ROPISA was synergistically driven by crystallization and solubility of the PLLA core. The versatility of the ROPISA process was also demonstrated by the successful preparation of nano-objects with poly(ε-caprolactone) (PCL) or poly(δ-valerolactone) (PVL) as the stabilizer block, and PLLA as the core-forming block. Based on the living and controlled character of ROPISA, in the final polymerization, the living species in the PLLA core could be in situ cross-linked by 4,4′-bioxepanyl-7,7′-dione (BOD) and the nano-objects could be stabilized. The melting temperature (T_m) of the polylactone blocks in the core or shell region was independent and unaffected. Comparing with the unstabilized nano-objects, the thermal stability of stabilized nano-objects can be significantly enhanced.