Biomedical Engineering Reference
In-Depth Information
Scheme 17
Synthesis of hyperbranched polymer through diyne polycyclotrimerization
A few research groups had looked into the possibility of utilizing the
alkyne cyclization for polymer synthesis in the early 1970s and late 1980s [59-
63]. But as summarized by Sergeyev et al. in a symposium review article [59]
at that time, the resultant homopolymers “are infusible and insoluble in
conventional organic solvents” and “are difficult to reprocess into manufac-
tured articles”. The interest in the alkyne homopolycyclotrimerization had
therefore subsided, with almost nobody revisiting the subject over the past
decades, because the insolubility of the homopolymers of the diynes rendered
their structural characterization a difficult proposition and their intractabil-
ity made them almost useless in terms of finding practical applications as
plastic materials.
2.4.1
Hyperbranched Poly(alkylenephenylene)s
We have studied homopolycyclotrimerizations of aliphatic terminal diynes
with various alkylene spacer lengths catalyzed by tantalum and niobium
halides or by binary mixtures of the metal halides and tetraphenyltin
(Scheme 18) [64-66]. Under optimized conditions, completely soluble diyne
homopolymers with high molecular weights (
M
w
up to
10
6
)andpre-
∼
1.4
×
