The
polymersomes were prepared using poly(ethylene glycol)-polystyrene
(PEG-PS) block copolymers with azide functionality in the side chain,
which self-assembled in water in well-defined vesicles. A bisoxazoline
ligand 17 with two
alkyne moieties was used to stabilize the polymer membrane via a
crosslinking reaction and which simultaneously introduced binding sites
for the metal catalyst Cu(I) (Figure 2a-2b). In order to achieve a high
catalyst loading the cross-linked polymersomes were incubated twice with
Cu(I) (Cu(I)-PLs, detailed synthetic procedure, and characterization are
given in the supporting information), leading to a Cu(I) content of
0.035 mol/L. The polymersome morphology (Figure 2c-2d), copper
distribution (Figure 2e), and oxidation state were determined (Figure
2f). Due to the presence of Cu(I), the polymersomes were visualized as
dark spheres.
Figure 2. (a), (b) Schematic representation of block copolymer
structures and cross-linked Cu(I) polymersomes (Cu(I)-PLs). (c) TEM
picture of Cu(I)-PLs after first loading with Cu(I); (d) TEM picture of
Cu(I)-PLs after second Cu(I) loading. (e) Copper distribution in the
membrane of Cu(I)-PLs (indicated in pink), derived by SEM-EDX
measurements. (f) XPS analysis on Cu(I)-PLs, to confirm the oxidation
state of Cu(I).
Firstly, after preliminary stability tests of Cu(I)-PLs under different
conditions (in the supporting information), the CuAAC reaction was
optimized in batch using the Cu(I)-PLs with the synthesized
2,6-difluorobenzyl azide and the 2 alkynes (R2, 2M) at
65 oC, and compared with CuI powder and the
homogeneous CuI-ligand complex (Cu(I): 0.05M, Table 2).
Table 2. Optimization of the batch reaction conditions.