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 ( ) (i.e., chain mobility) of the micelle core-forming blocks on micelle-unimer coexistence. We synthesized a series of seven PEG--P(BA-BA) amphiphilic block copolymers (PEG = poly(ethylene glycol), BA = -butyl acrylate, BA = -butyl acrylate) with similar molecular weights (12 kg/mol). Varying the BA/BA molar ratio enabled broad modulation of core block 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 from 25 to -46 °C. Additionally, unimer population at fixed polymer composition (and thus core ) 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.