Thermal behaviors of intrinsic polyaniline and its derivatives

ELSEVIER

Synthetic Metals

Thermal

behaviors

X. -II.

Wang,

69 (1995) 263-264

polyaniline

of intrinsic

Y. -H.

Geng,

Wang,

L. -X.

Polymer Physics Laboratory, Chemistry, Academia Sinica,

and its derivatives

X. -B.

Changchun Changchun

Jing+ and F. -S.

*

Wang

Institute of Applied 130022, P. R. China

Abstract Thermal properties of polyaniline (PAn) , polytoluidine (POT > and polyanisidine (PAS > were examined niques. The weight-uptake of POT at 200-3OO’C was observed and carefully discussed.

1. INTRODUCTION Preliminary study on thermal stability of polyaniline has been done[‘]. This paper will focus on thermal decomposition, thermal crosslinking and thermal oxidation of PAn, POT and PAS. 2. EXPERIMENTAL PAn, POT and PAS were synthesized according to the previously described procedure f”. PAn was fractionated into 3 (NMP) , fractions by extracting with N -methylpyrrolidinone dimethylformamide(DMF) and tetrahydrofuran(THF) consecutively. 3. RESULTS

* Project supported by

the National Natural Science corrcspondencc should bc addrcsscd

Foundation

of China

0319-6779/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI

is well below the onset temperature of decomposition of PAn (see Table 1). Therefore, this exothermal effect is not due to decomposition. When PAn was treated at 220°C for I5 minutes and its DSC curve was reccorded, the exothermal peak disappeared. Thus we attribute this peak to crosslinking of PAn molecules. Y. Wei et al. also found this crosslinking reaction at 25O’C for PAn filmc3’, this difference may be attributed to NMP contained in the film. In fact, after heating at 22O’C, PAn is not soluble any longer. The crosslinking is responsible for the low weight loss at 500’C of PAn (Table l), because crosslinking usually improves thermal stability. 30

AND DISCUSSION

3. 1. Thermal decomposition and thermal crosslinking Thermogravimetric analysis were carried out on various PAn fractions, POT and PAS of different molecular weight under nitrogen atmosphere. The onset temperature T, of decomposition and weight loss percentage are listed in Table I. Obviously, T, of PAn fractions increases greatly with increasing molecular weight. But the weight loss percentage at 500°C of PAn fractions has no appreciable difference. It is approximately 15%. Molecular weight dependence is not obvious. The T, of POT and PAS display similar molecular weight dependence, and generally speaking, POT and PAS have lower T, than PAn if they have similar molecular weight. POT and PAS give much higher weight loss at 500’C. Therefore, the thermal stability of PAn and derivatives is dependent of the molecular weight and the substitution of the benzene ring. This is understandable if the intermolecular interaction is taken into consideration, because low molecular weight and ring substitution always lead to weaker intermolecular interaction. DSC curve of common PAn powder is shown in Fig. 1. It shows an exothermal peak centered at 220’C. This temperature

i- To whom

by TG and DSC tech-

0379-6779(94)02442-Z

0 50

100

200

300

TEMPERATURE( Fig.

1 DSC

curves

of R-PAn(-

400

500

?? c) * -_),C-PAn(-_)

and P-

PAn(----_)powdcr

In order to examine the reaction of PAn crosslinking ,DSC curves of common PAn (C -PAn) , completely reduced -PAn (R-PAn) and pernigraniline-like PAn(P-PAn) were shown in Fig. 1. R-PAn dose not give appreciable exothermal peak and the exothermal peak of P-PAn is centered at 270-C. indicating that the crosslinking is closely related to the oxidation degree of PAn. Therefore, it can be concluded that thermal crosslinking of PAn takes place on the quinoid units.

264

X.-H.

Table 1 Molecular

weight and thermal PAn(1)

Mw/l@

properties

PAn(2)

126

M./lo3 T,,‘C Weight loss-at 500-c %

Wang et al. I Synthetic Metals 69 (1995) 263-264

of intrinsic PAn(3)

58

BAn PAS (1)

PAS (2)

POT (1)

POT (2)

64

20

102

21

17

22

12

6

10

5

14

5

432

390

232

250

196

340

290

67

68

36

42

13. 6

14. 4

15. 4

3

60’ -

F

a i=

60 -

p

s

40 20 so

40 t 201 50

‘\ ,

I

I

100

200

300

\

I 400

, 100

I 200

500

I 300

1 400

8 500

TEMPERATUREi ‘0

TEMPERATURE( ‘cl

Fig. 3 TGcurvcs (-

Fig. 2 TG curves of (-->,

POT

powder

prcparcd

* -->

and Oz(-

Nz(---)

at 20-C

un&r

noting

in its TG curve in air (see Fig. 2). IR spectrum the existence hours.

In addition,

copolymer

decreases

copolymer. oxidation weight

of carboxyl

weight

uptake

clearly indicates

group after it is treated

at 260% for 2

reduction

of toluidine

unit

in the

Thus the weight uptake may be due to the thermal of CH3 group to COOH group.

The disappearance

uptake under NZ atmosphere(crosslinking

pens instead

of thermal

temperature

under oxygencsee

provide further

evidence

oxidation)

and weight

reaction uptake

TG curve of POT-02

for the conclusion.

Fig. 3 shows

(POT -11,

??

??

->,POT-2

powder under air atmosphere.

of hap-

uptake

TG curves

p -phenylenediol

(POT - 3).

pared

temperature

at

lower

depends

greatly

of POT prepared

common POT treated

phenylenediol

the weight uptake of the aniline-toluidine with

POT(-_),POT-l(-

We find that the weight

atmoaphcre.

that POT displays

of common

and POT-3(---_)

air defect.

It is worthwhile

* ->

POT after treated

at - 1O’C

with vitamin C(POT -2)

It is well known has

less

chain

the decrease

defects,

uptake

REFERENCES 1. V. G.Kulkarni

et al. , Synth.

Met. , 30(1989)321.

2. L. Wang et al. , Acta Polymerica 3. Y. Wei et al. , Polymer,

Sinica,

33(1992)314.

of

that weight uptake

is closely related to radical type chain defect.

to low

in Fig. 2)

p -

POT treat-

of weight

by them really indicates

or

that POT pre-

and vitamin C are radical scavengers,

ed by them has less defect,

on chain

3(1989)264.