Biomedical Engineering Reference
In-Depth Information
Scheme 29
Proposed mechanism for 1,3,5-regioselective polycyclotrimerization of aryl
ethynyl ketone [102, 103]
much simpler, in comparison to their
hb
-PA congeners. The presence of three
basic structures of a hyperbranched polymer, viz.,
D
,
L
and
T
unites, was
readily verified by the number of reacted acetylene triple bonds in the re-
peat unit (Scheme 30). Because of the structural flexibility of the monomers,
especially
71
-
76
, the polymer branches can also be terminated by an addi-
tional dimerization end-capping reaction, in which two alkyne groups of the
same diyne molecule react with a ketoenamine to form a new benzene ring.
The end group resulting from this back-biting reaction is called “cyclophanic
terminal” (
T
c
). From their corresponding resonance peaks in the
1
HNMR
spectra, DB values of 78-100% were estimated. These values are much higher
than those of the “conventional” hyperbranched polymers, which are com-
monly in the neighborhood of 50% [107].
