Synthesis and Reaction of Well-defined Copolymers with Thermally Exchangeable Dynamic Covalent Bonds in the Side Chains

Abstract

Synthesis of well-defined linear copolymers with thermally exchangeable dynamic covalent bonds in their side chains and their structural interconversion system were demonstrated. The well-defined linear polymers with alkoxyamine moieties in their side chains were successfully prepared by the atom transfer radical polymerization (ATRP) method by tuning the reaction conditions. Random copolymer was successfully converted into macroscopic gel due to the cross-linking reaction between complementarily-reactive alkoxyamine units. From the results of gel permeation chromatography - multi-angle laser light scattering (GPC-MALLS) and small angle X-ray scattering (SAXS) measurements, it was made clear that the star-like nanogels are formed as the most stable structure in the diblock copolymer system. The molecular weights of the nanogels at equilibrium are clearly controlled by initial concentrations as well as the composition and molecular weights of the diblock copolymers. The structures of the nanogels were observed by scanning force microscopy (SFM) observation, which revealed that nanogels consisted of both a gel part and branching molecular chains. By controlling the stoichiometric ratio of added alkoxyamine, structural conversion from nanogels to diblock copolymer also proceeded, as the structures of the compounds depend on the equilibrium state.