ma0609578_si_001.pdf (152.52 kB)
Synthesis of Poly(n-butyl acrylate)-block-poly(acrylic acid) Diblock Copolymers by ATRP and Their Micellization in Water
journal contribution
posted on 2007-06-12, 00:00 authored by Olivier Colombani, Markus Ruppel, Frank Schubert, Heiko Zettl, Dmitry V. Pergushov, Axel H. E. MüllerAmphiphilic diblock copolymers, poly(n-butyl acrylate)-block-poly(acrylic acid) (PnBA-PAA), with
narrow molecular weight distribution (PDI ≤ 1.07) were prepared by atom transfer radical polymerization (ATRP)
of n-butyl acrylate and tert-butyl acrylate (tBA), followed by selective acidolysis of the PtBA block. These polymers
possess a soft PnBA hydrophobic block with a constant chain length of 90−100 monomer units and pH- and
ionic strength-sensitive hydrophilic PAA block with DPPAA = 33−300 AA monomer units. They were expected
to form stimuli-responsive micelles. The block copolymers with DPPAA ≥ 100 are directly soluble in water at pH
> 4.7. Pyrene steady-state fluorescence spectroscopy and fluorescence correlation spectroscopy (FCS) studies
indicate the existence of a very low critical micelle concentration (cmc ∼ 10-8 mol/L). The number-average
hydrodynamic radii of the micelles, as determined by FCS, range from 28 to 55 nm, depending on the PAA
block length. FCS data indicate that micellar sizes significantly decrease upon dilution for salt-free systems. This
is attributed to a dynamic, but kinetically controlled, behavior of these self-assembled nanostructures. In saline
solutions the micellar sizes remain constant above the “apparent” cmc (cmc*), which is attributed to slower
dynamics of unimer exchange between micelles.