Biomedical Engineering Reference
In-Depth Information
Scheme 28
1,3,5-Regioselective polycyclotrimerization of aroylarylenes
lyst, however, furnished soluble polymers in much shorter reaction times and
higher yields: for example,
hb
-P
71
(6) and
hb
-P
73
(4) were obtained in virtu-
ally quantitative yields after 24 hreaction.
As proven by the spectroscopic analyses, the aroyldiynes were regioselec-
tively polycyclotrimerized into
hb
-PAAs by piperidine. This regioselectivity
stems from the ionic mechanism of the base-catalyzed polycyclotrimer-
ization reaction [106]. Piperidine may have reacted with an aroylethynyl
group in a Michael addition mode to form a ketoenamine (
a
), which
further reacts with two more aroylethynyl groups to give a dihydroben-
zene (
d
; Scheme 29). The piperidine moiety of
d
is removed by its re-
action with another aroylethynyl group and aromatization gives a 1,3,5-
trisubstituted benzene ring
e
. Repeats of this cycle result in the formation of
an
hb
-PAA [105].
Again, with the help of spectral analyses, the hyperbranched structures of
the poly(aroylarylene)s were confirmed. Thanks to the 1,3,5-regioselectivity
of the cyclotrimerization reaction, the NMR spectra of the
hb
-PAAs were
