All-Polylactones\nNano-Objects Prepared by a One-Pot\nRing-Opening Polymerization-Induced Self-Assembly Process

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