Protonation Of Polyaniline With Lightly Sulfonated Polystyrene (Page 2 of 2) in pdf

104

Y. Fu, R.A. Weiss/SyntheticMetals 84 (1997) 103-104

increased

and correspondingly,

the intensity

of the quinoid

absorption peak at 640 nm decreased.

A very clear isosebestic

point at 730 nm was observed,

which

implies

that sulfonic

acid

groups

directly

protonate

the imine

nitrogen

and

transform the quinoid

units into semiquinoid

units as shown

below (01 y< 1):

This

conversion

between

quinoid

and semiquinoid

units is

reversible

and quantitative.

The amount

of sulfonic

acid

required

to reach the maximum

doping level was greater than

the theoretical

0.5 equivalent.

This reduction

of effective

protonation

of quinoid

rings of PAN1 may be due either to

conformation

hindrance

of the polymeric

sulfonic acid groups

or to solvent effects, or both.

go’

2 0.

s 0.

Wavelength (nm)

Fig. 2. UV-Vis

absorption

spectra of PAN1 base at different

concentration

of HSPS in NMP, concentration

of PAN1 is kept

constant

at 0.06

mM,

(a) [-S03H]/[AN]

= 0.0; (b) [-

S03H]/[AN]

= 1.1; (c) [-S03H]/[AN]

= 2.1; (d) [-SOgH]/[AN]

3.2.

The protonation

of PAN1 base with HSPS was also run in

NMP solution

to assess the solvent effect on doping behavior.

Fig. 2 shows the UV-Vis

absorption

spectra of different molar

ratios of HSPS/PANI

in NMP solution.

The absorption

peaks

for PAN1 base were blue shifted in NMP compared to those in

DMSO.

As the [HSPS]/[PANI]

ratio

increased,

a new

absorption

peak at 830 nm was observed due to the transition

from semiquinoid

rings.

Fig. 2 clearly shows that doping of

PAN1

by HSPS

in NMP

solution

does occur,

but the

protonation

is less effective than in DMSO,

and the acid

concentration

has to be more than doubled to reach the same

amount of doping level.

The semiquinoid

absorption

intensity

is proportional

the concentration

of the protonated

state of PANI, and the the

quinoid

absorption

intensity

is proportional

to the concen-

tration of the neutral state of PANI.

The ratios of absorption

intensity

of the protonated

states and the neutral

states

(Asemiquinoid/Aquinoid)

are plotted against the concentration

ratio of the sulfonic acid group and the aniline repeat unit,

2.5

1.5

0.5

1.5

2.5

3.5

[-S03H] / [AN]

Fig. 3. Protonation

of PAN1 base with HSPS as function of

[-S03H]/ [AN] ratios in DMSO and NMP.

[-S03H]/[AN],

in DMSO and NMP solutions in Fig. 3. When

[-SO3H]/[AN]

is less than 0.5,

Asemiquinoid/Aquinoid

essentially

zero in both solvents.

This indicates

that no

significant

amount of the protonated

state of PAN1 exists at

low [-SOgH]/[AN]

ratios.

Once the [-S03H]/[AN]

ratio is

above 0.5,

the Ascmiquinoid/Aquinoid

ratio

in DMSO

increases dramatically,

while the Asemiquinoid/Aquinoid

ratio

in NMP increases

at a much slower

rate.

The prevalent

hydrogen bonding between the carbonyl group of NMP and the

sulfonic

acid significantly

retards the protonation

of PAN1

base, because hydrogen bonding may reduce the available free

acid groups. We recently also observed undoping of PANI-CSA

in NMP solution

during dilution

with the color change from

green to blue. The transition

from an insulating

form to a

metalic

conductive

form of PANI

is evidenced

by a steep

increase

in the concentration

of protonated

material.

similar observation

for the effect of HCl concentration

on the

protonation

of PAN1 film was also reported by Wan [9].

Acknowledgment

We gratefully

acknowledge

financial

support

for this

work by Connecticut

Innovations,

Inc.

References

[ 11 E. M. Genies, A. Boyle, M. Lapkowski

and C. Tsintavis,

Syrtth. Met., 36 (1990),

139.

[2]

F. Lux, Polymer,

35 (1994), 2915.

[3]

Y. Cao, P. Smith and A. J. heeger, Synth. Mef., 48

(1992),

91.

[4] M. Angelopoulos

and N. Patel, Polym. Muter. Sci. Eng.,

71 (1994), 222.

[S] A. G. Macdiarmid,

J. Chiang, M. Halpern, W. Huang, S.

Mu, N. L. D. Somasiri, W. Wu and S. I. Yaniger, Mol.

Cryst. Liq. Cryyst., 121 (1985),

173.

[6] G. E. Asturias, A. G. MacDiarmid,

R. P. McCall and A. J.

Epstein, Synth. Met., 29 (1989), E157.

[7] H. S. Makowski,

R. D. Lundberg and G. H. Singhal, U.S.

Pat. 3,870,841,

(1975).

[X] K. Tzou and V. Gregory, Synth. Met., 53 (1993), 365.

[9] M. Wan, J. Polym. Sci., Polym. Chern. Ed., 30 (1992),

543.

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