Chemistry Reference
In-Depth Information
steric factors introduced by the substituents that force the double bonds in the polymeric chains to
twist out of coplanarity [
67
]. A family of substituted polyacetylenes were prepared [
68
] that were
actually formed from ethynylpyridines by a polymerization reaction that takes place spontaneously
by a quaternization process:
+
R
X
N
N
N
X
X
R
R
where X is a bromine or an iodine.
Like other substituted polyacetylenes, these materials are fairly stable in air and are soluble in
polar solvents, also in water. The conductivity of these polymers is improved over previously
reported substituted polyacetylenes to within the range of semiconductors.
Preparation of a highly conductive polyacetylene was achieved when Ziegler-Natta catalyst was
used by Shirakawa in aged silicone oil at 150
C. It is believed that this reaction results in formation of
polymers with less defects in the structures. The conductivity of these materials, when doped, actually
approaches that of copper [
62
].
Considerable progress has been achieved in development of catalyst systems for living polymeri-
zation of various substituted acetylenes during the last 10 or 15 years [
69
]. Nowadays, there are
available single-component catalysts based on stable carbene complexes and multicomponent
catalysts based on MoOCl
4
and WOCl
4
, both operating in metathesis mode, as well as Rh(diene)
complexes operating in the Ziegler-Natta mode.
For instance, a living polymerization of phenyl acetylene and the synthesis of an end-
functionalized poly(phenyl acetylene) by using Rh-based catalyst systems, [RhCI(nbd)]
2
/Ar
2
C
¼
C
¼
(Ph)Li/PPh
3
(Ar
Ph, 4-Me
2
-NC
6
H
4
), was reported [
70
]. Also, use of (triphenyl vinyl)lithium that
has functional groups, such as the dimethylamino groups, results in formation of end-functionalized
poly(phenyl acetylene)s, which quantitatively contained functional groups at the initiating chain end.
The polymerization of phenyl acetylene by a catalyst prepared from [RhCl(norbornadiene)]
2
,
Ph
2
C
¼
C(Ph)Li, and PPh
3
proceeds smoothly in benzene to give quantitatively a yellow polymer
with the number average molecular weight of 5,400 and the polydispersity ratio of 1.14. The reaction
can be illustrated as follows:
PPh
3
[RhCl (nbd)]
2
/
Ph
2
C=C (Ph) Li /
PPh
3
PPh
3
nHC
CPh
Ph
Ph
Rh
Rh
Ph
Ph
n
Ph
Ph
Ph
Masuda and colleagues reported [
71
] that they synthesized poly(anthryacetylenes)-bearing oligo
oxyethylene units by using a transition metal catalyst, WC1
6
, in 30 and 34% yields. The polymers
were black solids. These polymers are soluble in chloroform, tetrahydrofuran, acetone, etc., but
insoluble in alcohols, aliphatic hydrocarbons, etc. The UV-VS spectra of the polymers showed
absorption maxima and band edges at around 570 and 750 nm, respectively, indicating that the
polymer chains possess highly extended conjugation. These polymers exhibited blue emission
