Strong Variation of Micelle-Unimer Coexistence as a Function of Core Chain Mobility.

Polymeric micelles coexist in solution with unassembled chains (unimers). We have investigated the influence of glass transition temperature ( T g ) (i.e., chain mobility) of the micelle core-forming blocks on micelle-unimer coexistence. We synthesized a series of seven PEG- b -P( n BA- ran-t BA) amphiphilic block copolymers (PEG = poly(ethylene glycol), n BA = n -butyl acrylate, t BA = tert -butyl acrylate) with similar molecular weights (12 kg/mol). Varying the n BA/ t BA molar ratio enabled broad modulation of core block T g with no significant change in core hydrophobicity or micelle size. NMR diffusometry revealed increasing unimer populations from 0% to 54% of total polymer concentration upon decreasing core block T g from 25 to -46 °C. Additionally, unimer population at fixed polymer composition (and thus core T g ) increased with temperature. This study demonstrates the strong influence of core-forming block mobility on polymer self-assembly, providing information toward designing drug delivery systems and suggesting the need for new dynamical theory.