<s>
Polyacetylene	B-Language
(	O
IUPAC	O
name	O
:	O
polyethyne	B-Language
)	O
usually	O
refers	O
to	O
an	O
organic	O
polymer	O
with	O
the	O
repeating	O
unit	O
.	O
</s>
<s>
This	O
compound	O
is	O
conceptually	O
important	O
,	O
as	O
the	O
discovery	O
of	O
polyacetylene	B-Language
and	O
its	O
high	O
conductivity	O
upon	O
doping	B-Algorithm
helped	O
to	O
launch	O
the	O
field	O
of	O
organic	O
conductive	B-Algorithm
polymers	I-Algorithm
.	O
</s>
<s>
The	O
high	O
electrical	O
conductivity	O
discovered	O
by	O
Hideki	O
Shirakawa	O
,	O
Alan	O
Heeger	O
,	O
and	O
Alan	O
MacDiarmid	O
for	O
this	O
polymer	O
led	O
to	O
intense	O
interest	O
in	O
the	O
use	O
of	O
organic	O
compounds	O
in	O
microelectronics	O
(	O
organic	B-Algorithm
semiconductors	I-Algorithm
)	O
.	O
</s>
<s>
Early	O
work	O
in	O
the	O
field	O
of	O
polyacetylene	B-Language
research	O
was	O
aimed	O
at	O
using	O
doped	O
polymers	O
as	O
easily	O
processable	O
and	O
lightweight	O
"	O
plastic	O
metals	O
"	O
.	O
</s>
<s>
Despite	O
the	O
promise	O
of	O
this	O
polymer	O
in	O
the	O
field	O
of	O
conductive	B-Algorithm
polymers	I-Algorithm
,	O
many	O
of	O
its	O
properties	O
such	O
as	O
instability	O
to	O
air	O
and	O
difficulty	O
with	O
processing	O
have	O
led	O
to	O
avoidance	O
in	O
commercial	O
applications	O
.	O
</s>
<s>
Compounds	O
called	O
polyacetylenes	B-Language
also	O
occur	O
in	O
nature	O
,	O
although	O
in	O
this	O
context	O
the	O
term	O
refers	O
to	O
polyynes	O
,	O
compounds	O
containing	O
multiple	O
acetylene	O
groups	O
(	O
"	O
poly	O
"	O
meaning	O
many	O
)	O
,	O
rather	O
than	O
to	O
chains	O
of	O
olefin	O
groups	O
(	O
"	O
poly	O
"	O
meaning	O
polymerization	O
of	O
)	O
.	O
</s>
<s>
Polyacetylene	B-Language
consists	O
of	O
a	O
long	O
chain	O
of	O
carbon	O
atoms	O
with	O
alternating	O
single	O
and	O
double	O
bonds	O
between	O
them	O
,	O
each	O
with	O
one	O
hydrogen	O
atom	O
.	O
</s>
<s>
The	O
controlled	O
synthesis	O
of	O
each	O
isomer	O
of	O
the	O
polymer	O
,	O
cis-polyacetylene	O
or	O
trans-polyacetylene	O
,	O
can	O
be	O
achieved	O
by	O
changing	O
the	O
temperature	O
at	O
which	O
the	O
reaction	O
is	O
conducted	O
.	O
</s>
<s>
Despite	O
the	O
conjugated	O
nature	O
of	O
the	O
polyacetylene	B-Language
backbone	O
,	O
not	O
all	O
of	O
the	O
carbon	O
–	O
carbon	O
bonds	O
in	O
the	O
material	O
are	O
equal	O
:	O
a	O
distinct	O
single/double	O
alternation	O
exists	O
.	O
</s>
<s>
Substituted	O
polyacetylenes	B-Language
tend	O
to	O
be	O
more	O
rigid	O
than	O
saturated	O
polymers	O
.	O
</s>
<s>
One	O
of	O
the	O
earliest	O
reported	O
acetylene	O
polymers	O
was	O
named	O
Cuprene	B-Language
.	O
</s>
<s>
Linear	O
polyacetylene	B-Language
was	O
first	O
prepared	O
by	O
Giulio	O
Natta	O
in	O
1958	O
.	O
</s>
<s>
The	O
resulting	O
polyacetylene	B-Language
was	O
linear	O
,	O
of	O
high	O
molecular	O
weight	O
,	O
displayed	O
high	O
crystallinity	O
,	O
and	O
had	O
a	O
regular	O
structure	O
.	O
</s>
<s>
X-ray	O
diffraction	O
studies	O
demonstrated	O
that	O
the	O
resulting	O
polyacetylene	B-Language
was	O
trans-polyacetylene	O
.	O
</s>
<s>
After	O
this	O
first	O
reported	O
synthesis	O
,	O
few	O
chemists	O
were	O
interested	O
in	O
polyacetylene	B-Language
because	O
the	O
product	O
of	O
Natta	O
's	O
preparation	O
was	O
an	O
insoluble	O
,	O
air	O
sensitive	O
,	O
and	O
infusible	O
black	O
powder	O
.	O
</s>
<s>
The	O
next	O
major	O
development	O
of	O
polyacetylene	B-Language
polymerization	O
was	O
made	O
by	O
Hideki	O
Shirakawa	O
’s	O
group	O
who	O
were	O
able	O
to	O
prepare	O
silvery	O
films	O
of	O
polyacetylene	B-Language
.	O
</s>
<s>
They	O
discovered	O
that	O
the	O
polymerization	O
of	O
polyacetylene	B-Language
could	O
be	O
achieved	O
at	O
the	O
surface	O
of	O
a	O
concentrated	O
solution	O
of	O
the	O
catalyst	O
system	O
of	O
Et3Al	O
and	O
Ti(OBu )	O
4	O
in	O
an	O
inert	O
solvent	O
such	O
as	O
toluene	O
.	O
</s>
<s>
Shirakawa	O
,	O
Heeger	O
,	O
and	O
MacDiarmid	O
collaborated	O
on	O
further	O
development	O
of	O
polyacetylene	B-Language
.	O
</s>
<s>
Upon	O
doping	B-Algorithm
polyacetylene	B-Language
with	O
I2	O
,	O
the	O
conductivity	O
increased	O
seven	O
orders	O
of	O
magnitude	O
.	O
</s>
<s>
These	O
materials	O
exhibited	O
the	O
largest	O
room	O
temperature	O
conductivity	O
observed	O
for	O
a	O
covalent	O
organic	O
polymer	O
,	O
and	O
this	O
seminal	O
report	O
was	O
key	O
in	O
furthering	O
the	O
development	O
of	O
organic	O
conductive	B-Algorithm
polymers	I-Algorithm
.	O
</s>
<s>
Further	O
studies	O
led	O
to	O
improved	O
control	O
of	O
the	O
cis/trans	O
isomer	O
ratio	O
and	O
demonstrated	O
that	O
cis-polyacetylene	O
doping	B-Algorithm
led	O
to	O
higher	O
conductivity	O
than	O
doping	B-Algorithm
of	O
trans-polyacetylene	O
.	O
</s>
<s>
Doping	B-Algorithm
cis-polyacetylene	O
with	O
AsF5	O
further	O
increased	O
the	O
conductivities	O
,	O
bringing	O
them	O
close	O
to	O
that	O
of	O
copper	O
.	O
</s>
<s>
To	O
account	O
for	O
such	O
an	O
increase	O
in	O
conductivity	O
in	O
polyacetylene	B-Language
,	O
J	O
.	O
R	O
.	O
Schrieffer	O
and	O
Heeger	O
considered	O
the	O
existence	O
of	O
topologically	O
protected	O
solitonic	O
defects	O
,	O
their	O
model	O
is	O
now	O
known	O
as	O
the	O
Su	O
–	O
Schrieffer	O
–	O
Heeger	O
model	O
,	O
which	O
has	O
served	O
as	O
model	O
in	O
other	O
contexts	O
to	O
understand	O
topological	O
insulators	O
.	O
</s>
<s>
A	O
variety	O
of	O
methods	O
have	O
been	O
developed	O
to	O
synthesize	O
polyacetylene	B-Language
,	O
from	O
pure	O
acetylene	O
and	O
other	O
monomers	O
.	O
</s>
<s>
By	O
varying	O
the	O
apparatus	O
and	O
catalyst	O
loading	O
,	O
Shirakawa	O
and	O
coworkers	O
were	O
able	O
to	O
synthesize	O
polyacetylene	B-Language
as	O
thin	O
films	O
,	O
rather	O
than	O
insoluble	O
black	O
powders	O
.	O
</s>
<s>
Enkelmann	O
and	O
coworkers	O
further	O
improved	O
polyacetylene	B-Language
synthesis	O
by	O
changing	O
the	O
catalyst	O
to	O
a	O
Co(NO3 )	O
2/NaBH4	O
system	O
,	O
which	O
was	O
stable	O
to	O
both	O
oxygen	O
and	O
water	O
.	O
</s>
<s>
Polyacetylene	B-Language
can	O
also	O
be	O
produced	O
by	O
radiation	O
polymerization	O
of	O
acetylene	O
.	O
</s>
<s>
Glow-discharge	O
radiation	O
,	O
gamma	O
radiation	O
,	O
and	O
ultraviolet	B-Application
irradiation	O
have	O
been	O
used	O
.	O
</s>
<s>
Gas-phase	O
polymerization	O
typically	O
produces	O
irregular	O
cuprene	B-Language
,	O
whereas	O
liquid-phase	O
polymerization	O
,	O
conducted	O
at	O
−78°C	O
produces	O
linear	O
cis-polyacetylene	O
,	O
and	O
solid-phase	O
polymerization	O
,	O
conducted	O
at	O
still	O
lower	O
temperature	O
,	O
produces	O
trans-polyacetylene	O
.	O
</s>
<s>
Polyacetylene	B-Language
can	O
be	O
synthesized	O
by	O
ring-opening	O
metathesis	O
polymerisation	O
(	O
ROMP	O
)	O
from	O
cyclooctatetraene	O
,	O
a	O
material	O
easier	O
to	O
handle	O
than	O
the	O
acetylene	O
monomer	O
.	O
</s>
<s>
Robert	O
Grubbs	O
and	O
coworkers	O
synthesized	O
a	O
variety	O
of	O
polyacetylene	B-Language
derivatives	O
with	O
linear	O
and	O
branched	O
alkyl	O
chains	O
.	O
</s>
<s>
They	O
obtained	O
soluble	O
and	O
conductive	B-Algorithm
polymers	I-Algorithm
with	O
sec-butyl	O
and	O
neopentyl	O
groups	O
,	O
because	O
the	O
methylene	O
(	O
CH2	O
)	O
unit	O
directly	O
connected	O
to	O
the	O
polymer	O
reduces	O
steric	O
crowding	O
and	O
prevents	O
twisting	O
.	O
</s>
<s>
Polyacetylene	B-Language
can	O
also	O
be	O
synthesized	O
from	O
precursor	O
polymers	O
.	O
</s>
<s>
This	O
method	O
enables	O
processing	O
of	O
the	O
polymer	O
before	O
conversion	O
to	O
insoluble	O
polyacetylene	B-Language
.	O
</s>
<s>
Short	O
,	O
irregular	O
segments	O
of	O
polyacetylene	B-Language
can	O
be	O
obtained	O
by	O
dehydrohalogenation	O
of	O
poly(vinyl chloride )	O
.	O
</s>
<s>
Thermal	O
conversion	O
of	O
precursor	O
polymers	O
is	O
a	O
more	O
effective	O
method	O
for	O
synthesizing	O
long	O
polyacetylene	B-Language
chains	O
.	O
</s>
<s>
When	O
polyacetylene	B-Language
films	O
are	O
exposed	O
to	O
vapors	O
of	O
electron-accepting	O
compounds	O
(	O
p-type	O
dopants	O
)	O
,	O
the	O
electrical	O
conductivity	O
of	O
the	O
material	O
increases	O
by	O
orders	O
of	O
magnitude	O
over	O
the	O
undoped	O
material	O
.	O
</s>
<s>
The	O
conductivity	O
of	O
these	O
polymers	O
is	O
believed	O
to	O
be	O
a	O
result	O
of	O
the	O
creation	O
of	O
charge-transfer	B-Algorithm
complexes	I-Algorithm
between	O
the	O
polymer	O
and	O
halogen	O
.	O
</s>
<s>
Charge	B-Algorithm
transfer	I-Algorithm
occurs	O
from	O
the	O
polymer	O
to	O
the	O
acceptor	O
compound	O
;	O
the	O
polyacetylene	B-Language
chain	O
acts	O
as	O
a	O
cation	O
and	O
the	O
acceptor	O
as	O
an	O
anion	O
.	O
</s>
<s>
Polyacetylene	B-Language
doped	O
with	O
(	O
p-type	O
)	O
dopants	O
retain	O
their	O
high	O
conductivity	O
even	O
after	O
exposure	O
to	O
air	O
for	O
several	O
days	O
.	O
</s>
<s>
Electron-donating	O
(	O
n-type	O
)	O
dopants	O
can	O
also	O
be	O
used	O
to	O
create	O
conductive	O
polyacetylene	B-Language
.	O
</s>
<s>
n-Type	O
dopants	O
for	O
polyacetylene	B-Language
include	O
lithium	O
,	O
sodium	O
,	O
and	O
potassium	O
.	O
</s>
<s>
As	O
with	O
p-type	O
dopants	O
,	O
charge-transfer	B-Algorithm
complexes	I-Algorithm
are	O
created	O
,	O
where	O
the	O
polymer	O
backbone	O
is	O
anionic	O
and	O
the	O
donor	O
is	O
cationic	O
.	O
</s>
<s>
Polyacetylene	B-Language
chains	O
doped	O
with	O
n-type	O
dopants	O
are	O
extremely	O
sensitive	O
to	O
air	O
and	O
moisture	O
.	O
</s>
<s>
Polyacetylene	B-Language
can	O
also	O
be	O
doped	O
electrochemically	O
.	O
</s>
<s>
The	O
conductivity	O
of	O
polyacetylene	B-Language
depends	O
on	O
structure	O
and	O
doping	B-Algorithm
.	O
</s>
<s>
Undoped	O
trans-polyacetylene	O
films	O
have	O
a	O
conductivity	O
of	O
4.4	O
×10−5	O
Ω−1cm−1	O
,	O
while	O
cis-polyacetylene	O
has	O
a	O
lower	O
conductivity	O
of	O
1.7	O
×10−9	O
Ω−1cm−1	O
.	O
</s>
<s>
Doping	B-Algorithm
with	O
bromine	O
causes	O
an	O
increase	O
in	O
conductivity	O
to	O
0.5	O
Ω−1cm−1	O
,	O
while	O
a	O
higher	O
conductivity	O
of	O
38	O
Ω−1cm−1	O
is	O
obtained	O
through	O
doping	B-Algorithm
with	O
iodine	O
.	O
</s>
<s>
Doping	B-Algorithm
of	O
either	O
cis	O
-	O
or	O
trans-polyacetylene	O
leads	O
to	O
an	O
increase	O
in	O
their	O
conductivities	O
by	O
at	O
least	O
six	O
orders	O
of	O
magnitude	O
.	O
</s>
<s>
Doped	O
cis-polyacetylene	O
films	O
usually	O
have	O
conductivities	O
two	O
or	O
three	O
times	O
greater	O
than	O
doped	O
trans-polyacetylene	O
even	O
though	O
the	O
parent	O
film	O
has	O
lower	O
conductivity	O
.	O
</s>
<s>
The	O
structure	O
of	O
polyacetylene	B-Language
films	O
have	O
been	O
examined	O
by	O
both	O
infrared	O
spectroscopy	O
and	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
and	O
found	O
that	O
the	O
structure	O
depends	O
on	O
synthetic	O
conditions	O
.	O
</s>
<s>
Films	O
of	O
cis-polyacetylene	O
are	O
very	O
flexible	O
and	O
can	O
be	O
readily	O
stretched	O
,	O
while	O
trans-polyacetylene	O
is	O
much	O
more	O
brittle	O
.	O
</s>
<s>
The	O
synthesis	O
and	O
processing	O
of	O
polyacetylene	B-Language
films	O
affects	O
the	O
properties	O
.	O
</s>
<s>
Polyacetylene	B-Language
has	O
a	O
bulk	O
density	O
of	O
0.4g/cm3	O
,	O
while	O
density	O
of	O
the	O
foam	O
is	O
significantly	O
lower	O
,	O
at	O
0.02	O
–	O
0.04g/cm3	O
.	O
</s>
<s>
The	O
insolubility	O
of	O
polyacetylene	B-Language
makes	O
it	O
difficult	O
to	O
characterize	O
this	O
material	O
and	O
to	O
determine	O
the	O
extent	O
of	O
cross-linking	O
in	O
the	O
material	O
.	O
</s>
<s>
For	O
applications	O
,	O
polyacetylenes	B-Language
suffer	O
from	O
many	O
drawbacks	O
.	O
</s>
<s>
While	O
both	O
cis	O
and	O
trans-polyacetylene	O
show	O
high	O
thermal	O
stability	O
,	O
exposure	O
to	O
air	O
causes	O
a	O
large	O
decrease	O
in	O
the	O
flexibility	O
and	O
conductivity	O
.	O
</s>
<s>
When	O
polyacetylene	B-Language
is	O
exposed	O
to	O
air	O
,	O
oxidation	O
of	O
the	O
backbone	O
by	O
O2	O
occurs	O
.	O
</s>
<s>
Polyacetylene	B-Language
has	O
no	O
commercial	O
applications	O
,	O
although	O
the	O
discovery	O
of	O
polyacetylene	B-Language
as	O
a	O
conductive	O
organic	O
polymer	O
led	O
to	O
many	O
developments	O
in	O
materials	O
science	O
.	O
</s>
<s>
Conducting	B-Algorithm
polymers	I-Algorithm
are	O
of	O
interest	O
for	O
solution-processing	O
for	O
film-forming	O
conductive	B-Algorithm
polymers	I-Algorithm
.	O
</s>
<s>
Therefore	O
,	O
attention	O
has	O
shifted	O
to	O
other	O
conductive	B-Algorithm
polymers	I-Algorithm
for	O
application	O
purposes	O
including	O
polythiophene	B-Algorithm
and	O
polyaniline	B-Algorithm
.	O
</s>
<s>
Molecular	B-Algorithm
electronics	I-Algorithm
could	O
also	O
be	O
a	O
potential	O
application	O
of	O
conductive	O
polyacetylene	B-Language
.	O
</s>
