Biomedical Engineering Reference
In-Depth Information
Fig. 2
Three-dimensional macromolecular structure of
hb
-P
66
simulated by Materials Stu-
dio program.
Inset
:Chemicalstructureof
hb
-P
66
(
upper panel
)andsimplifiedillustration
of the two-dimensional geometric structure of
hb
-P
66
(
lower panel
)
10
5
)inhighisolation
yields (up to 99.7%) [88, 92-98]. 1-Alkynes (V-VIII) are generally better
comonomers than 1-arylacetylenes (IX-XI) when the molecular weights of
the
hb
-PAsareconcerned.Thisisprobablyduetotwoeffects.First,the
long alkyl chains may confer higher solubility on the propagating species,
therefore enabling their continued, further growth into bigger polymers. The
second might be associated with an electronic effect. The electron-donating
alkyl groups make the triple bonds of 1-alkynes electronically richer, which
are likely to favorably interact with the electron-poorer aromatic diynes [99],
hence promoting the formation of high molecular weight
hb
-PAs.
As a nice example, a “true”
hb
-PP without any substituent groups
(or a “pure”, all-aromatic plastic) was readily synthesized by the copoly-
cyclotrimerization of diethynylbenzene (
38
) with phenylacetylene (IX)
(Scheme 26). Whilst its cousin of linear PPP becomes insoluble and in-
tractable when the molecular weight of PPP reaches just a few thousands, the
highly branched and irregular molecular structure of
hb
-P(
38
-X) hampers
strong
arylenes with high molecular weights (
M
w
up to
∼
1.8
×
stacking of the aromatic rings, making the polymer completely
soluble in common organic solvents.
π
-
π
