Conducting polymer blends

S.vJ2thetic Metals, 28 (1989) C467 C471

C467

CONDUCTING POLYMER BLENDS

J. LAAKSO, J.-E. OSTERHOLM and P. NYHOLM Neste Oy, Corporate R&D, SF-06850 Kulloo, Finland

ABSTRACT

We r e p o r t the production and properties of electrically conducting polymer blends utilizing the melt-processability p r o p e r t i e s of high m o l e c u l a r weight p o l y ( 3 - o c t y l t h i o p h e n e ) , POT. We have amounts

found t h a t polymer blends produced by mixing a p p r o p r i a t e of POT w i t h a v a r i e t y of t h e r m o p l a s t i c m a t r i x polymers

have e x c e l l e n t

mechanical

yield electrically e x c e e d i n g I S/cm.

properties

conducting

and t h a t

polymer

they can be doped to

blends

with

conductivities

INTRODUCTION

Since the discovery of conducting polymers in 1977 [ I ] , not u n t i l

recently that

in some of the c r i t i c a l

s i g n i f i c a n t breakthroughs

it

was

have been made

properties of conjugated organic polymers

that might open the way of these novel materials to useful technological applications. The most c r i t i c a l properties of conducting

polymers are environmental, high temperature stability and processability. Significant improvements in e n v i r o n m e n t a l s t a b i l i t y and p r o c e s s a b i l i t y , both s o l u t i o n and m e l t - p r o c e s s a b i l i t y , have r e c e n t l y been r e p o r t e d f o r d e r i v a t i v e s of p o l y t h i o p h e n e s [ 2 ] . I t has been observed t h a t in c o n t r a s t to p o l y t h i o p h e n e , PT, and poly(3-methylthiophene), P3MeT, which are n o n - p r o c e s s a b l e , p o l y ( 3 alkylthiophenes), P3ATs ( F i g . I ) , t h a t c o n t a i n long a l k y l c h a i n s , s u b s t i t u t e d at the 3 - p o s i t i o n of the t h i o p h e n e r i n g , are s o l u b l e in common o r g a n i c 0379-6779/89/$3.50

solvents

and m e l t - p r o c e s s a b l e

at c o n v e n i e n t

© Elsevier Sequoia/Printed in Tile Netherlands,

C468

S

S

L~ Fig. I .

Poly(3-octylthiophene)

temperatures

without

decomposition

observed m e l t - p r o c e s s a b i l i t y of

[2].

As a consequence of the

P3ATs i t

is possible to produce

polymer blends using ordinary melt-processing techniques

[2].

In t h i s work we report the production and properties of blends of

POT and a v a r i e t y of matrix polymers such as ethylene vinyl

acetate,

(EVA), ethylene butyl

acrylate, (EBA), polystyrene, (PS)

and polyethylene (PE). We have found that these blends are dopable using well-known doping techniques

to y i e l d e l e c t r i c a l l y conduct-

ing polymer blends. EXPERIMENTAL

POT

used

in

this

w o r k was

prepared

different

chemical polymerization

Osterholm

et

al.

[2].

techniques

As-synthesized

p a r t i a l l y c r y s t a l l i n e solid,

chemically as

using

two

described

POT-powder, which

shows a melting temperature

is

by a

of ca.

160 °C which makes i t very useful to melt-processing with ordinary thermoplastics. We have used a Brabender Plasticorder PLV 151 for melt-mixing of POT and the matrix polymer. such as temperature combination

of

The mixing conditions

and shear rate were chosen according

to the

POT and the matrix polymer used. Films and sheets

of the polymer were made using compression molding at 180-220 °C at 100 bar for 5 min [ 2 ] . Doping of these blends was done by immersion in nitromethane solutions of f e r r i c chloride (0.1 M, washed with dry nitromethane, dried in vacuum) or in s t a t i c vacuum with iodine vapour. RESULTS AND DISCUSSION

In Table I we show the e l e c t r i c a l c o n d u c t i v i t i e s of some selected POT-containing blends doped by iodine and FeCl3. We find

C469 that

the

conductivity

trolled

by

polymer

or

given the

in

varying a

the

the

Table

I

of

are not

blends

a variety

conductivities

them

can the

conveniently

doping

all.

The

time,

rather

indicate

electrically

spanning

from

conductivities

of

less

be the

that

con-

matrix

conductivity

t h e maximum c o n d u c t i v i t i e s

but

of

blends

POT-content,

combination

respective

achieve

of

values

obtainable

it

is

conducting

polymer

blends

than

S/cm to

more

10 -10

in

possible

to with

than

I

S/cm. TABLE i Electrical

Blend

POT c o n t e n t

Although

the

decline

with

able

and

it

i0 20 20 10 10 20 10

a considerable thus

blends.

Using

blends

conductivities in this

this

obtainable

preliminary

Since

the

homogeneity

of

the

dopant

molecules

matrix

polymer

of

this

is

given

EVA/POT

nitromethane. through

the

chemical doping

and

to

it

of

investigated are

easily

should

the

and

be

the

to

matrix

anisotropy

conditions

anticipate

tend

stretch-

possible

POT w i t h i n

electrical

stretching

will

be much h i g h e r

than

reported

are

governed

that

swellable

in

of the

in

carefully electrical

those

reported

of

the

of

the

chosen

blends, film

respectively,

EVA/POT a u n i f o r m is

PE t o w a r d s

i n the case o f

observed. organic PE/POT.

post-doped

of

matrix

a rapid

the

polymer

diffusion

blends

require

solvent.

2 where we show d o p a n t

case o f

m thick

choice

doping,

interior

Fig.

here

by t h e

solution

their

PE/POT

achieved

that

they

we

Using

is in

inertness is

is

In t h e 150

blends

10 .5 10 .3 10 .2 10 .4

type

blends

doping

technique.

of

I 6.0 1.0 3.7 1.0

the

optical

10 .4 10 - I

study.

polymer

and d o p i n g the

both

controlled

of

of

orientation

creating

(S/cm)

8.0 3.0

POT-content,

therefore,

achieve

selected

strength

increasing

appears,

Conductivity

iodine iodine FeCI 3 iodine FeCI 3 FeCI 3 FeCI 3

tensile

polymer the

Dopant

(~)

EVA/POT EVA/POT EVA/POT EBA/POT EBA/POT PE/POT PS/POT

to

some POT b l e n d s

of that

An example

profile

analysis

doped

by

dopant

distribution

In c o n t r a s t , solvents,

only

FeCI 3 due to

in the

a surface

C470

The

percolation

processed

polymer

dispersability combination

blends

of of

threshold

molecular

between

conductivities containing possible which

of

EVA/POT, the

observed

course,

weight

these

types

largely

of

depend

distributions

(which

percolation % of

threshold

POT.

We

however,

right

influences In the

has r e p r o d u c i b l y

have,

melt

on the

polymer used and thus

the blend components are i m p o r t a n t .

5-10 2-3

produce

would

properties

of

in

been

observed

in the range of ]0 .6 to 10 .4 S/cm in EVA/POT blends

only to

will,

POT and the m a t r i x

the m e l t - v i s c o s i t y ) case of

achievable

be

% of blends

important

POT which with both

very what

indicate low

that

it

percolation

comes

to

the

should

be

thresholds mechanical

of the doped blends and to the economics.

SO11

e.O

H ] CROIIETERS

~.~. 8

I00

rz

0.0

MICROMETERS

3000.0

Fig. 2. SEM curves of FeCI 3 doped EVA/POT (upper curve) blends.

and PE/POT

C471

Investigations port

[4]

on e l e c t r i c a l

as w e l l

these types of e l e c t r i c a l l y elsewhere. currently

properties

as on e n v i r o n m e n t a l

Optimization

conducting

as w e l l

[3]

and charge

and thermal

trans-

stability

[5]

of

polymer blends are r e p o r t e d

as u p - s c a l i n g

of

the

blends

are

in p r o g r e s s .

CONCLUSIONS

We have shown t h a t a wide

variety

blends doped

melt-processable

matrix

polymers

with

excellent

mechanical

using

different

doping

conducting span

of

the

P3ATs can be d i s p e r s e d

in

the

molten

properties.

techniques

These

thus

polymer blends whose c o n d u c t i v i t y entire

conductivity

believe

that

further

development of

important

this

concept

range will

from

be

conducting

of

state blends

giving

vital

can be

electrically to m e t a l s .

importance

into

in

give

can be c o n t r o l l e d

insulators

polymers

to

to

to We the

many c o m m e r c i a l l y

applications.

ACKNOWLEDGEMENTS

We are indebted to Chem. Eng. Viveca L6nnberg, Mononen and Lab. Tech. assisting

Sari

Lab. ~ech.

in the polymer s y n t h e s i s and blends p r e p a r a t i o n .

acknowledge

Analytical samples.

Pirjo

K a r j a l a i n e n of Neste Corporate R&D f o r

Department,

analyzing

our

This

work

(Finland)

and Nordisk I n d u s t r i f o n d

Neste

Corporate

was supported

in

We also R&D

part

for

by TEKES

(Norway).

REFERENCES

1. C. K. Chiang,

C. R. F i n c h e r ,

H. Shirakawa, Lett.,

E. J.

39 (1977)

Louis

Jr.,

and A.

Y. W. Park, A. J. G. MacDiarmid,

Heeger,

Phys.

Rev.

1098.

2. J . - E . Osterholm, J. Laakso, P. Nyholm, H. I s o t a l o , H. Stubb, O. Ingan~s and W.R. Salaneck, and r e f e r e n c e s t h e r e i n , Synth. Met., 28 (1989) C435 (these P r o c e e d i n g s ) . 3.

4.

H. I s o t a l o , H. Stubb, P. Y l i - L a h t i , P. K u i v a l a i n e n , J . - E . Osterholm and J. Laakso, Synth. M e t . , 28 (1989) C461 (these Proceedings). H. I s o t a l o , J.

Laakso,

nen and P. Y l i - L a h t i , 5. J . - O .

Nilsson,

Salaneck, J . - E .

J.-E.

~sterholm,

H. Stubb,

P. K u i v a l a i -

to be p u b l i s h e d .

G. Gustafsson, O. Ingan~s, ~sterholm and J.

C445 (these P r o c e e d i n g s ) .

K. Uvdahl, W.R.

Laakso, Synth.

Met.,

28 (1989)