Overview

• Introduction

• Conducting polymers

• Polyaniline (PAni)

• Limitations

• Aim of study

• Elastomers

• Methodology - Discussion

• Synthesis of polyaniline

• Preparation and properties of blends – 1 : EO-EPI Elastomer

• Preparation and properties of blends – 2 : NBR Elastomer

Conclusions

Conducting Polymers

• Conjugated organic macromolecules

• Conduct electricity in the “DOPED” state (i.e. when charged)

POTENTIAL APPLICATIONS

• Electrochromic and electro-luminescent devices

• Anti-corrosion paints & coatings

• Radar absorbing materials

• Printed circuits

• Antistatics

Polyaniline

Why Polyaniline ?

• Monomer inexpensive (aniline)

• High yield polymerisation & low-toxicity polymer

• High thermal and environmental stability

• Good electrical and optical properties

Drawbacks of PAni for industrial applications ?

� Low processability

� Poor mechanical properties

Polyaniline

Conductivity=2.6x10-8 S/cm Conductivity=9.8S/cm

• Electrical properties reversibly controlled via protonation

N

NN

N

n

H

H

N

NN

N

n

H

H

H

H

X X

+ +. .

- -Low pH

High pH

Aim of study

• Synthesis, optimisation and analysis of conducting PAni

• Blending solubilised PAni with elastomers

Conducting rubbers with good electrical & mechanical props.

Elastomer 1

Epichlorohydrin-ethylene oxide

• Similar solubility parameter and H-bonding potential to

polyanilines

• Strong, flexible backbone

• Good oil, fuel and solvent resistance.

• Good heat resistance.

CH2 n

CH

CH2

Cl

OCH2

Om CH

2

Synthesis of Polyaniline

Chemical polymerisation Chemical polymerisation ---- twotwo--step route chosen:step route chosen:

•• Synthesis of Synthesis of PAniPAni Hydrochloride saltHydrochloride salt

•• DeprotonationDeprotonation to prepare to prepare PAniPAni basebase

•• ReprotonationReprotonation (doping) of base with (doping) of base with solubilisingsolubilising

agent, e.g. ionic surfactant or other agent, e.g. ionic surfactant or other sulfonicsulfonic acid acid

NH2

(NH4)2S

2O

8+

N NNN

n

HH

H HCl Cl

++. .

- -

Temp. 0 oC

pH=0-0.5

1 M HCl

Oxidative polymerisation

Polyaniline - HCl

Effect of oxidant/monomer ratio on conductivity of Polyaniline.HCl

(� Optimum value is surprisingly sub-stoichiometric)

0

2

4

6

8

10

12

0 0.25 0.5 0.75 1 1.25 1.5 1.75

Ratio of Oxidant/Monomer

Co

nd

uctivity S

/cm

0.75

Polyaniline Base

N NNN

n

HH

H HCl Cl

++. .

- -

NN NN

n

H

H

Deprotonation of the salt0.5 M

NH4OH

Doping (ReDoping (Re--protonatingprotonating) ) PAniPAni BaseBase

N N

H

N N

Hn

CH3SO

3H

SO3H

C12

H25

SO3H

CH3

SO3H

SOO

O

H

O

(DBSA)

Conductivity and Solubility Parameters

� Only PAni.DBSA gave a reasonable match…

PolymerConductivity

(S.cm-1)

Solubility parameters (J.cm-3)1/2

Epi-EO 2x10-10 19.9

PAni-DBSA 0.6 20.8

PAni-CSA 0.9 22.9

PAni-MeSA 2.7 23.9

PAni-TSA 1.6 24

PAni-NSA 1.5 25

Preparation of Blends

Blends prepared by co-dissolution method

• Polymers (PAni.DBSA & EPI.EO) dissolved in THF

• Solvent evaporated on PTFE sheets to obtain

conducting blend films

PTFE sheet

PAni.DBSA

Blended with

EPI / EO

UV-Vis Analysis of PANI.DBSA BLENDS

� Shows the dispersed polyaniline remains in conductive state

200 300 400 500 600 700 800 900

Wavelength (nm)

Ab

so

rban

ce

Pani Base Pani-DBSA 20% Pani-DBSA

773nm

628nm

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

0 10 20 30 40 50 60

Weight fraction of PAni-DBSA

Lo

g e

lectr

ica

l co

nd

ucti

vit

y (σ

)

Conductivity of Pani.DBSA Blends

� Percolation threshold apparently <1vol.%

(Some elongated particles present, as well as larger “globules”)

(a) Before percolation

(b) After percolation

(c) Totally connected

1%

GLASS TRANSITION OF PANI-DBSA BLENDS

� also indicate that the PAni.DBSA dissolves in the elastomer

Blends Blends PANIPANI--DBSA DBSA

Content (wt%)Content (wt%)Tg Tg oCC

EpiEpi--EOEO 00 --4040

PAniPAni--DBSA/EpiDBSA/Epi--EOEO 1010 --3737

PAniPAni--DBSA/EpiDBSA/Epi--EOEO 2020 --3636

PAniPAni--DBSA/EpiDBSA/Epi--EOEO 2525 --3535

PAniPAni--DBSA/EpiDBSA/Epi--EOEO 33.333.3 --3333

PAniPAni--DBSA/EpiDBSA/Epi--EOEO 5050 --2323

TGA analysis of PANI-DBSA BLENDS… reveals a compositional trend in the high-T degradation event

0

20

40

60

80

100

0 100 200 300 400 500 600

Temperature / oC

We

igh

t %

100% Pani-DBSA 100% Rubber 10% Pani-DBSA 20% Pani-DBSA 33.3% Pani-DBSA 50% Pani-DBSA

300-370oC

290-355oC

280-335oC

270-320oC

200-400oC

10% Pani-DBSA 20.0% Pani-DBSA

50.0% Pani-DBSA

Blend Morphology : Optical Microscopy (200x)�Reveals PAni-rich and PAni-poor regions on the µm scale

(both contribute to bulk conductivity)

33.3% Pani-DBSA

Summary

• Increasing oxidant ratio � higher concentration radical cations

shorter polymer chain � lower conductivity

• Increased pH � decrease level of protonation � lower

conductivity

• PAni-DBSA has good compatibility with Epi-EO elastomer

• Level of conductivity of the blends can be modified according to

desired application

• Percolation threshold of blends ~1% w/w

• UV-visible spectrometry shows PAni-DBSA remains in the

doped form upon blending with Epi-EO copolymer.

INTRODUCTION

� Elastomer-intrinsically conducting polymer blends were prepared by:

� Solution mixing, i.e. by using a shared solvent

� Mechanical mixing, using an internal mixer

� Criteria for selection of main components:

� High chemical attack resistance (elastomer).

� Good solubility and miscibility with selected partner-polymer (for elastomer and conductive polymer).

� Good thermal stability (both polymers).

� Good electrical conductivity (conductive polymer).

� Both polymers were blended by using solution mixing, with chloroform as the shared solvent

� NBR (with 48 wt% acrylonitrile content) and PAni.DBSA were chosen as the elastomer and conducting polymer respectively

Solubility Parameter Values

� Calculated by using Equation 1 and molar attraction constant s

calculated by Hoy.

Equation 1 : δp = (ρ x ΣFi) / Mo

where δp = solubility parameter for polymer , ρ = density of polymer , Σfi = sum of group molar attraction constants of

polymer repeat unit & Mo = formula weight of the polymer repeat unit

Polymer Solubility Parameter Value (J.cm-3)1/2

NBR

(48 wt% ACN content)

PAni.DBSA

20.8

20.8

FT-IR Spectroscopy

� Spectra of blend films resemble a superposition of spectra for NBR and PAni.DBSA but a few notable peak shifts provide evidence of molecular-scale interaction between the two polymers

Pure material/

blend (wt%

NBR:wt% PAni.DBSA)

Peak assignment (cm-1). Indication of peak intensity: W, weak; M, medium

=N-H

stretching

S=O

stretching

-CΞN

stretching

PAni.DBSA

NBR

Blends

90:10

50:50

3447W

-

3411W

3437W

1030M

-

1081W

1029W

-

2237M

2237W

2236W

DSC Analysis

� Samples of pure NBR, pure PAni.DBSA and their blends (with 10, 20, 30, 40 and 50 wt% of added PAni.DBSA) analyzed by DSC (-30oC to 400oC, heating rate 20oC/min).

� DSC thermograms of all blends show some degree of temperature shifting for their thermal processes (based on the onset value of endotherm or exotherm)

� Blends with 10 to 30% PAni.DBSA showed largest shifts. Other evidence showed good miscibility for these blends

DC Electrical Conductivity

� 100 µm films of pure NBR, pure PAni.DBSA and their blends were cast onto glass slides for this purpose

� Electrical conductivity measured by van der Pauw 4-probe technique, except for films with low conductivity (<10-7 S/cm) which were measured by using a 2-probe technique

� Apparently two stages of conductivity percolation, with thresholds < 1 vol.% and ~16 vol.% of PAni.DBSA

Electrical Conductivity of NBR-

PAni.DBSA Blends as a Function of

PAni.DBSA Content(� 2 stages of percolation apparent)

-16

-14

-12

-10

-8

-6

-4

-2

0

0 10 20 30 40 50

PAni.DBSA loading (wt%)

Lo

g c

on

du

cti

vit

y (

S/c

m)

Optical Microscopy

� All blends studied by optical microscopy (200 x magnification) and images captured digitally

� As before, the observed bright green regions are well-blended regions of both components (rich in NBR). TEM

reveals nano-sized particles & in these regions.

� The dark green regions (rich in PAni.DBSA) are large

particles or agglomerates of PAni. DBSA

Optical Micrographs for Blends: (a) with 5 wt% of

Added PAni.DBSA and (b) with 40 wt% of Added

PAni.DBSA

(a) (b)

125 µm125 µm

Thermal Mixing/Cross-

Linking of NBR Blends

� Polymers blended in an internal mixer

(Brabender)

� Cross-linked by dicumyl peroxide

� Vulcanisation studied by MDR

� Samples characterised as for solvent-cast

blends

� Anisotropic mechanical & electrical

properties (i.e. parallel & perpendicular to

flow) also measured

Mean Glass Transition Temperatures (Tg) for

Peroxide-Vulcanised NBR and NBR-PAni.DBSA

Blends

Composition

(wt% NBR : wt% PAni.DBSA*)

Glass transition temperature (Tg), oC

Vulcanised NBR (48.2 wt% ACN)

Vulcanised blends

90:10

80:20

70:30

60:40

50:50

-10

-7

-7

-5

-8

-8

Tensile Strength of Blends vs.

Composition� PAni gives some initial reinforcement,

then weakens the rubber

1

1

11.5

12

12.5

13

13.5

14

0 10

2030 40 50

Added PAni.DBSA (wt%)

Te

Tensile

str

ength

(M

Pa)

Test pieces parallel to flow direction

Test pieces perpendicular to flow direction

Electrical Conductivity

� Un-strained samples: surprisingly little effect of

thermal treatment or cross-linking

-16

-14

-12

-10

-8

-6

-4

-2

0

0 10 20 30 40 50

Added PAni.DBSA (wt%)

Lo

g C

on

du

cti

vit

y (

S.c

m-1

)

-16

-14

-12

-10

-8

-6

-4

-2

0

0 10 20 30 40 50

Added PAni.DBSA (wt%)

Lo

g C

on

du

cti

vit

y (

S.c

m-1

)

Non-vulcanised Peroxide-Vulcanised

Electrical Conductivity:

Effect of Strain - 1

� 10% Pani.DBSA Blend - 3rd cycle

(shows little fatigue)

-5.53

-5.525

-5.52

-5.515

-5.51

-5.505

-5.5

-5.495

-5.49

0 20 40 60 80 100

Elongation in Length (%)

Lo

g C

on

du

cti

vit

y (

S.c

m-1

)

Loading Unloading

-5.542

-5.54

-5.538

-5.536

-5.534

-5.532

-5.53

-5.528

-5.526

0 20 40 60 80 100

Elongation in Length (%)L

og

Co

nd

uc

tiv

ity

(S

.cm

-1)

Loading Unloading

Strain parallel to flow (milling) direction

Strain perpendicular to flow

Electrical Conductivity:

Effect of Strain - 2

� 30% Pani.DBSA-NBR Blend (3rd cycle again)

-2.6

-2.55

-2.5

-2.45

-2.4

-2.35

-2.3

0 20 40 60 80 100

Elongation in Length (%)

Lo

g C

on

du

cti

vit

y (

S.c

m-1

)

Loading Unloading

-2.568

-2.566

-2.564

-2.562

-2.56

-2.558

-2.556

0 20 40 60 80 100

Elongation in Length (%)L

og

Co

nd

uc

tiv

ity

(S

.cm

-1)

Loading Unloading

Strain parallel to flow direction

Strain perpendicular to flow

CONCLUSION

� Polyaniline-nitrile rubber blends with reasonable miscibility and useful electrical properties have been prepared. (Miscibility between both polymers could be further improved by using a coupling agent.)

� Intermolecular interactions revealed by IR peaks and DSC transition temperatures shifts

� Two stages of conductivity percolation threshold observed. The earlier one corresponds to the well-blended phase and the later one to the separated phase.

� Thermal blends: conducting polymer appears to have both reinforcing or plasticising effects on NBR

� Conductivity of strained samples is anisotropic; samples strained in the flow direction show a repeatable increase in conductivity under tension.

� Mechanism still under analysis .

Acknowledgements

PEO-ECH Blends:

• Dr Zaid Abbas

• Dr. S. Barton

• Dr Ahmed Farid (London Metropolitan University)

NBR and ENR Blends:

�Malaysian Rubber Board

�Dr. Stuart Cook (TARRC,Hertford)

�Dr. Huda Morgan

�Dr. Andrew Tinker (Director of R&D, TARRC)

�Dr K-C Yong (on study leave from MRB)

Some Relevant Publications

1. The Effects of Composition and Processing Variables on the Properties of Thermoplastic Polyaniline Blends and Composites. H Morgan, PJS Foot and NW Brooks, J Mater. Sci. 36, 5369-77 (2001).

2. The Electronic Properties of Metal-Complexed Poly(3-Alkylthiophene) Films. PJS Foot, M Miah, V Montgomery and I Youngs, Mater. Res. Bull. 37, 2055-66 (2002).

3. Thermal Doping of Polyaniline by Sulfonic Acids. D Poussin, H Morgan and PJS Foot, Polymer International 52, 433-38 (2003).

4. Synthesis and properties of a novel thiophene conducting copolymer with mesogenic groups attached parallel to the polymer backbone. J W Brown, G J Lambe, P J S Foot and J A Clipson. Macromol. Rapid Commun. 25, 1000 (2004).

5. Synthesis of Liquid Crystalline Conducting Polymers for Laser Alignment. J W Brown, P J S Foot, L Gabaston, P Ibison and A Prevost. Macromolecular Chemistry & Physics 205, 1823 (2004).

6. Conductive Poly(Butadiene-co-Acrylonitrile)-Polyaniline Dodecylbenzenesulfonate [NBR-PAniDBSA] Blends prepared in Solution. K C Yong, P J S Foot, S J Cook and A J Tinker, European Polymer J. 42, 1716-27 (2006)

7. Conductive Polyaniline/Poly (Epichlorohydrin-co-Ethylene Oxide) Blends Prepared in Solution. Z K Abbas, S J Barton, P J S Foot and H Morgan. Polymers and Polymer Composites 15, 1-8 (2007).

8. Electrically-Conductive Epoxidised Natural Rubber-Polyaniline DBSA Blends. KC Yong, PJS Foot, H Morgan, S Cook, A Tinker, M Ahmad, J Rubb. Res. 11, 59-77 (2008).

9. Synthesis and Characterisation of Polyaniline/Montmorillonite Nanocomposites. A Shakoor, T Z Rizvi and P J S Foot, Polym. Polym. Comp. 17 (6), 347-52 (2009).

10. Properties of Thermally-Mixed Poly(Butadiene-co-Acrylonitrile)-PolyanilineDodecylbenzenesulfonate Blends. Submitted to J. Appl. Polym. Sci.