ARTICLE IN PRESS
JID: CCLET
[m5G;August 14, 2021;9:50]
Z. Lu, B. Guo, Y. Zhao et al.
Chinese Chemical Letters xxx (xxxx) xxx
Scheme 3. The process of P3 package QD and the fluorescence spectra of P3 (blue line), QD (black line) and P3-QD (red line).
and 1570 cm l correspond to -C=C- and -C=N- stretching, respec-
−
is introduced to investigate the inner structure of the particles
(Figs. 3a-d). Surprisingly, the obtained particles are not micelles
but vesicles, whose thickness are around 10 nm and diameters
are in the range of 130-750 nm. This is the first example of the
self-assemble of non-amphiphilic cyclic polymer to form vesicle. To
prove the self-assemble of P3 during reprecipitation process, quan-
tum dots (QD) and P3 are dissolved by DMF and then precipitated
in methanol (Scheme 3). In this process, the self-assemble of P3
generates vesicles contained QD inside. The obtained white solid
(named P3-QD) is washed with abundant methanol to remove any
dissociative QD. Then, the fluorescence spectra of P3, QD and P3-
QD are characterized and shown in Scheme 3. P3 shows broad
emission band in the range of 380-700 nm. Two sharp peaks are
detected in 416 and 339 nm, respectively. QD presents a strong
emission band in the range of 520-800 nm, and the strongest
emission peak locates at 582 nm. P3-QD presents almost the same
emission band, proving the incorporation of QD in P3 vesicles dur-
ing the reprecipitation process.
tively [50].
A conclusion could be drawn by the above-mentioned results is
that neither diazo group nor alkyne group is the chain end group
of the obtained polypyrazoles. Therefore, quadrupole time-of-flight
LC/MS (LC-QTOF-MS) was introduced to analyze the detail struc-
ture of polypyrazoles and P3 was chosen as the study object. The
polymerization of M3 was carried out in 2 h to obtain P3 with low
Mn. The LC-QTOF-MS spectrum of P3 with m/z from 1300 to 1900
is shown in Fig. 2. Regular repeating patterns spaced by m/z 124.03
are recorded, which is in agreement with the mass weight of M3
(
m/z 124.03), as well as the repeat unit of P3. The main m/z peaks
+
in the range of 1380 to 1770 can be sorted as [Na + P3] series,
which match quite well with the following mass formulae:
m/z = 22.9898 + 124.03m, m = 11 − 14;
where m means the number of the repeat unit of P3. Importantly,
no molecular weight of the end groups is found, which proves P3
is a cyclic polymer.
It is worthwhile to ensure how the self-assemble of P3 occur
during the reprecipitation. In that case, we repeat the reprecipi-
tation process again. The difference compared to previous exper-
iment is the additional of trace amount of TFA in methanol (The
pH of methanol is 6.5). The FT-IR is used to check the obtained
polymer (P3) and the spectrum is shown in Fig. S7 (Supporting
information). Comparing to the P3 obtained by pure methanol, it
The thermal properties of the obtained polypyrazoles were ex-
amined by differential scanning calorimetry (DSC) and thermo-
gravimetric analysis (TGA). Fig. S3 (Supporting information) shows
the DSC curves of the obtained polymers, and glass transition tem-
peratures (Tg) between 42.3 °C and 55 °C were observed (Table S2
in Supporting informaiton). Comparing to the linear polypyrazoles,
the Tg of the cyclic polypyrazoles sharply decreases [40]. The TGA
curves (Fig. S4 in Supporting information) of the polypyrazoles in-
dicated that all the obtained polymers were thermally stable, los-
ing merely 5% of their weights at temperatures higher than 181
−1
is found that a new and intense band around 1785 cm
arises,
which causes by the partially broken of hydrogen bond formed by
the N-H and ester group on the main chain of P3. It is proved that
the broken of hydrogen bond induce the partial increasement in
wavenumber [51]. Besides, TEM is used to further confirm the hy-
pothesis. As shown in Fig. 3e, the vesicle structure of P3 is de-
stroyed in presence of TFA. These results suggest that the forma-
tion of vesicle is induced by the hydrogen bond formed by the N-H
and ester group of polypyrazoles.
°
C (Table S2). The degradation of the obtained polymers was di-
vided into two main stages when they are heated under nitrogen
from room temperature to 600 °C, as evidenced by the derivative
thermogravimetric (DTG) analysis (Fig. S4). The UV-vis absorption
spectra of diluted solution of P3 in DMSO are also shown (Fig. S5
in Supporting information). Remarkable absorption bands in the
range of 260-400 nm are presented, which belong to the π-π tran-
sition and n-π transition [40].
After the crude products are purified by reprecipitation with
DMF/methanol, scanning electron microscopy (SEM) is used to
investigate the morphologies of the produced polymers (P1-P4),
where particles with wrinkle surface and diameters of 100-220
nm are observed (Fig. S6 in Supporting information). Then, TEM
In summary, one-step synthesis of polypyrazole by the 1,3-
diploar cycloaddition of AB type monomers that contain diazo and
alkyne groups is carried out, which provides a convenient pro-
cess to obtain cyclic polymer without any catalyst and solvent.
The successfully synthesis of cyclic polypyrazoles is proved by the
results of 1H NMR, 13C NMR, FT-IR, and LC-QTOF-MS. Further-
more, the polypyrazoles self-assemble into vesicles with diameter
in the range of 130-750 nm during the reprecipitation process with
5