Protonation Of Polyaniline With Lightly Sulfonated Polystyrene printable pdf download

ELSEVIER

Synthetic

Metals

84 (1997)

103-104

Protonation of polyaniline with lightly sulfonated polystyrene

Yueping Fu, R. A. Weiss

Polymer Science Program and Department

of Chemical Engineering

UniversiQ

of Connecticut,

Storrs, CT 06269-3136,

UsA

Abstract

Protonation

of polyaniline

base with lightly sulfonated polystyrene in polar solvents such as dimethyl

sulfoxide

(DMSO)

and

N-methyl

pyrrolidone

(NMP)

was investigated

by UV-Vis

absorption

spectroscopy.

The isosbestic

point clearly

shows that

quinoid

unit and semiquinoid

unit are in equilibrium

and is a function

of the sulfonic

acid concentration.

The protonation

polyaniline

is retarded in NMP compared to DMSO due to prevalent hydrogen bonding.

keywords:

Polyaniline,

sulfonated

polystyrene,

UV-Vis

absorption

1. Introduction

Polyaniline

(PANI)

has very promising

industrial

appli-

cations because of its good environmental

stability and facile

synthesis

[I, 21. Polyaniline

doped

with

organic

protonic

acids [3], and polymeric

acid [4] shows improved

solubility

and processibility.

We are interested in preparing

conductive polymer blends

with improved

processability

and better controlled

conduc-

tivity.

Theoretically,

the conductivity

of polyaniline

can be

varied from lo-lo

to 10 S/cm as a function of doping level. In

reality, the conductivity

of polyaniline

increases dramatically

at low doping level and levels off at ca. 10% doping [.5]. Here,

lightly

sulfonated

polystyrene

(HSPS)

was chosen

as the

polymer

matrix,

because the randomly

placed sulfonic

acid

groups on the polystyrene

chains behave as a dilute acid.

will

protonate

the imine nitrogen

sites of polyaniline,

while

possibly

retaining

the processability

of polystyrene.

This

molecular

protonation

should promote

compatibility

between

polyaniline

and

polystyrene

within

the

blends,

and

simultaneously

transform

the insulating

polyaniline

base

form to the metallic

conducting

form, thereby rendering

the

blends conductive.

The use of polymeric

dopants may signi-

ficantly improve

the stability of the resulting

polymer blends,

because small molecule

dopants

tend to migrate

out of the

polymer

matrix.

In this paper, we present direct evidence of doping PAN1

through

protonation

by sulfonic

acid groups of lightly

sulfo-

nated polystyrene

in solutions

and its dependence

on the

solvent environment.

Experimental

PANI was synthesized

by the oxidative

polymerization

of aniline

1.0

aqueous

HCl

with

ammonium

peroxydisulfate

(APS) as oxidant, as described previously

[6].

Polystyrene

(M, = 100,000, M,

= 280,000) was sulfonated to

5.3 mol % in dichloroethane

at 50 OC with

acetyl sulfate

following

the procedure

of Makowski

et al [7].

PANI/HSPS

solutions

with

different

molar ratios were

prepared

by mixing

appropriate

volumes of two solutions,

mM PAN1 base (based on the approximate

aniline

repeat unit

-CgHqNH-

) in DMSO or NMP and 10 mM HSPS (based on

0379-6779/97/%17.00

0 1997

Elswier

Science

S.A. All

rights

reserved

PII SO3794779(96)03857-X

styrene unit) in the same solvent, to give a clear solution,

keeping the concentration

of PANI constant at 0.06 mM. UV-

Vis absorbance spectra were recorded on Perkin-Elmer

Lambda

6 UV/VIS

spectrophotometer.

3. Results

and

discussion

The UV-Vis

absorption

spectra of different

ratios

PANI/HSPS

in DMSO solution are shown in Fig. 1. The PANI

base has two absorption

peaks at 335 nm and 640 nm.

The

absorption

peak at 335 nm is due to the rc-TC* transition

benzenoid

rings, while the absorption

peak at 640 nm is due

to the X-Z*

transition

of quinoid rings on the PAN1 chain.

“I

‘II

-I’

I”

“I

‘*.

I-’

“I

0.5

g 0.4

0.3

JJ 0.2

0.1

0.0

300

400

500

600

700

800

900

Wavelength

(nm)

Fig. 1. UV-Vis

absorption

spectra of PANI base at different

concentration

of HSPS in DMSO,

concentration

of PAN1 is

kept constant at 0.06 mM, (a) [-S03H]/[AN]

= 0.0;

(b) [-S03H]/[AN]

= 0.75; (c) [-S03H]/[AN]

= 1.1

When PAN1 base solution was mixed with HSPS in DMSO

solution,

a clear green solution

resulted.

This indicates

that

the HSPS can induce solubility

of the polyaniline

salt in the

same way as an organic

acid dopant.

The UV-Vis

spectra

showed a new absorption peak at 820 nm due to protonation

the imine sites of PANI.

This absorption

peak originates

from

the polaron

band transition,

which is also observed by proto-

nation with organic acid in solution

[8]. As the molar ratio of

HSPS to PAN1 increased,

the intensity

of the 820 nm peak

Protonation Of Polyaniline With Lightly Sulfonated Polystyrene

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