Biomedical Engineering Reference
In-Depth Information
gel point by simply pouring the reaction mixture into acidified methanol.
Soluble, high molecular weight
hb
-PYs of triynes like
17
and
19
,whoseCu-
catalyzed homopolycoupling proceeded very fast, could be obtained by their
copolycoupling with monoynes such as I.
In the polycoupling reactions, the formation of the diyne units proceeded
via a Glaser-Hay oxidative coupling route [35-38]. Despite its wide applica-
tions in the preparation of small molecules and linear polymers containing
diyne moieties, its mechanism remains unclear [38-40]. It has been proposed
that a dimeric copper acetylide complex is involved, whose collapse leads to
the formation of the diyne product (Scheme 9).
Scheme 9
Acetylene activation via
-complexation with copper(I) and proposed mechan-
ism for the formation of diacetylene bond via cuprated alkyne dimers
π
Because of the one-step polymerization procedure, hyperbranched poly-
mers often contain not only
D
and
T
but also
L
repeating units. This can
be expressed by DB, which is an important structural parameter of hyper-
branched polymers. DB is estimated as the sum of the
D
and
T
units divided
by the sum of all the three structural units, that is,
D
,
T
and
L
[41]. By
definition, a linear polymer has no dendritic units and its DB is zero, while
a perfect dendrimer has no linear units and its DB is thus unity. Frey has
pointed out that DB statistically approaches 0.5 in the case of polymerization
of AB
2
monomers, provided that all the functional groups possess the same
reactivity [42]. The structures of the
hb
-PYs could be analyzed by spectro-
scopic methods such as NMR and FTIR. The DB value of the phosphorous-
containing polymer
hb
-P
21
, for example, was estimated to be 53%fromits
31
P NMR chemical shifts (Chart 1).
The spectroscopic analyses revealed that both the homo- and copolyynes
contained terminal triple bonds, which offers a nice opportunity to decorate
