Self-assembly of PEG/dodecyl-graft amphiphilic copolymers in water: consequences of the monomer sequence and chain flexibility on uniform micelles

Abstract

Self-assembly of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl-graft amphiphilic copolymers in water was investigated in detail, by especially focusing on the effects of the monomer sequence and chain flexibility on the size controllability, mobility, and the thermoresponse of micelles. For this, we designed and synthesized PEG/dodecyl graft copolymers with different sequence distributions, backbones, compositions, and chain lengths via controlled or free radical copolymerization: acrylate random, methacrylate/acrylate gradient and bidirectional gradient, and methacrylate random block. Acrylate-based amphiphilic random copolymers produced uniform micelles in water, whose size was determined just by the composition. The flexible acrylate-based micelles had higher mobility of graft PEG and in-core dodecyl units than methacrylate counterparts yet effectively maintained uniform and compact size (∼10 nm) up to a high concentration. Additionally, the sequence distribution critically affected the size controllability of micelles. Gradient or random block copolymers with highly biased and/or locally accumulated hydrophobic monomer segments provided micelles with different sizes and/or broad size distributions. Thus, it was revealed that the random, statistical, and non-biased sequence distribution of hydrophilic and hydrophobic monomers is a key factor to efficiently induce composition-dependent precision self-assembly of PEG/dodecyl-graft copolymers into uniform size micelles in water.