Co-assembly Towards Janus Micelles - Self Organized Nanostructures of Amphiphilic Block Copolymers - page 169

Fig. 6 2D 1 H NMR NOESY contour plot of a 1:1 mixture of PAA 42 - b -PAAm 417 and P2MVP 42 - b -
PEO 446 in D 2 O at 1 mM NaNO 3 . The circles indicate where cross-peaks would appear

in case of close contact between PAAm and PEO chains. Adapted from [ 16 ]

( f + = 0 . 50 )

(Figs. 4 b and 6 ) [ 15 , 16 , 61 ]. We then extended our experimental studies with two
additional pairs of neutral polymers, to assess whether other types of chain segrega-
tion may also be observed experimentally.
Poly( N -methyl-2-vinyl pyridinium iodide)- block -poly(ethylene oxide), P2MVP 38
- b -PEO 211

and poly(acrylic acid)- block -poly(isopropyl acrylamide), PAA 55 - b -

PNIPAAm 88 , were mixed under stoichiometric conditions ( f + = 5, pH 7.7, 1 mM

NaNO 3 ) at room temperature [ 17 ]. Spherical micelles were obtained with a hydro-
dynamic radius of about 14 nm and a micellar mass of roughly 380 kg mol − 1 ,i.e.
each micelle contains

0 .

11 PAA 55 - b -PNIPAAm 88
copolymers. The micelles consist of a mixed PAA/P2MVP core and PEO/PNIPAAm
corona, as deduced from the presence of cross-peaks between PEO and PNIPAAm
protons in the NOESY contour plots (Fig. 4 a ). Interestingly, we are able to tune
the solvency of the PNIPAAm chains with temperature: the polymer has a lower
critical solution temperature (LCST) of about 32 ◦ C. Hence, at room temperature,
the present experimental system corresponds to an A-B/C-D mixture with two
charged monomers A and C, and two neutral hydrophilic monomers B and D
(denoted system II in Sect. 1 ) , and conversely, to an A-B/C-D mixture with two
charged monomers A and C, one neutral hydrophobic monomer B, and one neutral
hydrophilic monomer D (denoted system III). Hence, at elevated temperatures,
i.e. above the LCST, we expect a structural rearrangement into a three-layered

∼ 16 P2MVP 38 - b -PEO 211 and ∼