posted on 2021-07-02, 16:35authored byRyan J. Carrazzone, Xiuli Li, Jeffrey C. Foster, Veera Venkata Shravan Uppala, Candace E. Wall, Alan R. Esker, Louis A. Madsen, John B. Matson
Polymeric
micelles coexist in solution with unassembled chains
(unimers). We have investigated the influence of glass transition
temperature (Tg) (i.e., chain mobility)
of the micelle core-forming blocks on micelle–unimer coexistence.
We synthesized a series of seven PEG-b-P(nBA-ran-tBA) amphiphilic
block copolymers [PEG = poly(ethylene glycol), nBA
= n-butyl acrylate, and tBA = tert-butyl acrylate] with similar molecular weights (12
kg/mol). Varying the nBA/tBA molar
ratio enabled the broad modulation of core block Tg 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 Tg from 25 to −46 °C.
Additionally, unimer population at fixed polymer composition (and
thus core Tg) 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 a new dynamical
theory.