10.1002/anie.201905089
Angewandte Chemie International Edition
COMMUNICATION
reduce the interfacial tension, thus promoting unimer exchange.
The block copolymers P(S-co-AA)-b-PAA[10b,c,d] and P(nBA-stat-
AA)-b-PAA[10e] are two examples. Here, during the self-assembly
of PEG45-b-P(DEAEMA36-co-TPEMA6) and their CO2/Ar-driven
shape transformation, we have implemented effectively both
strategies. PEG45-b-P(DEAEMA36-co-TPEMA6) was first self-
assembled into vesicles in a dynamic way using THF or dioxane
as the co-solvent in the nanoprecipitation process. The final
vesicles dispersed in water after dialysis were, however, frozen.
Then, bubbling CO2 into the polymersome dispersion in water
induced the protonation of the amine groups in DEAEMA36,
which is equivalent to the introduction of some hydrophilic units
in the hydrophobic block. Consequently, the interfacial tension
decreased again, the aggregates “de-froze”, and the polymer
self-assemblies started to re-organize dynamically. After the
hydrophobic-hydrophilic transition of DEAEMA36, the core-
forming block became smaller because its main composition
was TPE-containing segments TPEMA6 and the amphiphilic
block copolymer initially ready for vesicle formation tended then
to form micelles with higher interfacial curvature. This was
actually observed by cryo-EM as shown in Figure 4c. It is
accepted in general that for flexible and amorphous copolymers
when the hydrophilic/hydrophobic weight ratio changes from low
value (e.g. 30/70) to high value (e.g. 45/55), the shape of self-
assembly changes from vesicles to spherical micelles.[12] Very
interestingly this process was reversible here. Upon the
subsequent Ar bubbling, an inverse hydrophilic-hydrophobic
transition of protonated DEAEMA36 took place and the core-
forming block became bigger again because its composition
included both TPEMA6 and DEAEMA36. The amphiphilic block
copolymer was again ready for vesicle formation. Upon the
increase of the degree of DEAEMA36 deprotonation during Ar
bubbling process, the hydrophilic/hydrophobic ratio decreased
gradually. Therefore, the dynamic re-organization included a
series of transformations: from spherical micelles to cylindrical
micelles, from cylindrical micelles to bilayer sheets and from
bilayer sheets to vesicles. If the whole process kept dynamic, we
would eventually find only polymer vesicles. But, giant and small
vesicles together with a few intermediate morphologies like
sheets and spherical and cylindrical micelles were observed
after 40 min of Ar bubbling where the conductivity and the pH
value of the solution reached steady level (Figure 4d and Figure
S16). This can be explained as follows. Upon Ar bubbling, the
deprotonation advanced with time and the interfacial tension
between hydrophobic block and the solvent increased gradually.
Consequently, the system became less and less dynamic and
intermediates shapes were “frozen”. The presence of a few of
frozen states could also explain why the conductivity and the pH
value could nearly return to the initial values, but not completely.
In fact, a few of protonated DEAEMA units might be confined in
the hydrophobic cores and their deprotonation became difficult
or impossible at the end.
DEAEMA/TPEMA contents and hydrophilic/total copolymer
ratios (17% to 30%) self-assembled into AIE polymersomes in
water using the nanoprecipitation method with THF and dioxane
as co-solvent, respectively. The PEG45-b-P(DEAEMA36-co-
TPEMA6) polymersomes were studied as an example for their
CO2/Ar-driven shape transformation. A reversible polymersome-
micelle transition was actually observed: polymer vesicles were
transformed to small spherical micelles upon CO2 bubbling; upon
subsequent Ar bubbling micelles returned to vesicular structures
coexisting with
a few intermediate morphologies. These
fluorescent polymersomes that can be opened by CO2-stimulus
may have potential applications in the design of CO2-related bio-
sensors and in the controlled drug delivery with in situ bio-
distribution tracing.
Acknowledgements
This work was financially supported by the French National
Research Agency (ANR-16-CE29-0028). Dapeng Zhang and
Yujiao Fan gratefully acknowledge China Scholarship Council
for funding their PhD scholarship.
Keywords: Polymersomes • carbon dioxide • aggregation-
induced emission • block copolymers • shape transformation
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In summary, novel CO2 responsive amphiphilic PEG-b-
P(DEAEMA-co-TPEMA) block copolymers with unspecified
(probably random) distribution of monomers DEAEMA and
TPEMA in the hydrophobic block have been prepared by RAFT
polymerization. The copolymers possess AIE property because
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