Uni-molecular nanoparticles of poly(2-oxazoline) showing tunable thermoresponsive behaviors

Herein, cylindrical molecular bottlebrushes grafted with poly(2-oxazoline) (POx) as a shaped tunable uni-molecular nanoparticle were synthesized via the grafting-onto approach. First, poly(glycidyl methacrylate) (PGMA) backbones with azide pendant units were prepared via reversible addition fragmentation transfer (RAFT) polymerization followed by post-modification. The degree of polymerization (DP) of the backbones was tuned in a range from 20 to 800. Alkynyl-terminated POx side chains were synthesized by living cationic ring opening polymerization (LCROP) of 2-ethyl-2-oxazoline (EtOx) and 2-methyl-2-oxazoline (MeOx), respectively. The DP of side chains was varied between 20 and 100. Then, the copper-catalyzed azide-alkynyl cycloaddition (CuAAC) click chemistry was conducted with a feed ratio of [alkynyl]:[azide] = 1.2:1 to yield a series of brushes. Depending on the DP of side chains, the grafting density ranged between 47 and 85%. The resulting brushlike nanoparticles exhibited shapes of sphere, rod and worm. Aqueous solutions of PEtOx brushes demonstrated a thermoresponsive behavior as a function of the length of backbones and side chains. Surprisingly, it was found that the lower critical solution temperature of PEtOx brushes increased with a length increase of backbones. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017