Preparation of chiral conducting polymer colloids

ELSEVIER

Synthetic

Preparation J.N. Bar&i, Intelligent

Polymer

Research

of Chiral

Metals

84 (1997)

Conducting

PC. Innis, L.A.P. Kane-Maguire,

Laborafo

y,

University

181-182

Polymer I.D. Norris

of Wollongong.,

Colloids

and G. G. Wallace.

Norfkjields

Avenue,

Wollongong

NSW 2522,

Australia

Abstract A novel method for the electrochemical synthesis of chiral conducting polyaniline (PAn) colloids has been developed, via the potentiostatic (+0.9V vs Ag /A&l) olyrnerisation of aniline in the presence of either (lR)-(-)-lo-camphorsulfonic acid ((-)- HCSA) or (lS)-(+)-lo-camphorsu s onic acid ((+)-HCSA). The electrosynthesis was performed under hydrodynamic conditions in an electrochemical flow cell using pol ethylene oxide as a stabiliser. The optical activity of the colloidal polyaniline dispersion was established by circular drc.lT roism (CD) spectroscopy. Visible region CD bands were observed at ca. 420 nm and were attributed to the macroasymmetry of the polyaniline salt chains. Mirror image CD ectra were obtained for colloids grown in the presence of (+)- or (-)-HCSA, suggestmg enantioselectivity during colloidal salt T ormation. Keywords

: Chiral

polyaniline

colloid,

optical

activity,

electropolymerization.

Introduction The preparation of conducting polymer colloids has been shown to rovide an attractive route to overcoming the problems tfl at are associated with processin these materials. It is well known that inherently con 3 ucting polymers are for the most part intractable, being insoluble in common solvents and infusible, making thermal processing im ssible. It has been established that stable conducting po Tymer colloids can be formed via a chemical oxidation m the presence of a steric stabiliser [l-3]. More we have demonstrated that with the use of

We have shown recently that the incorporation of (lR)(-)- or (lS)-(+)-lo-camphorsulfonic acid ((+)- or (-)-HCSA), into polyaniline films induces o tical activity in the conducting olymer backbone [6-8 7. The purpose of the present stu x y was to determine if such optical activity could also be induced into colloidal materials produced electrochemically.

Membrane I

(BDH)

was distilled

before

use. (+)- and (-)-

Polyaniline ((+ - or (-)-HCSA) colloids thesised in a divi ed electrochemical :gwninFiy e 1. The’ cell was divided b membrane Neosepta AMH A-2119, To 03794779/97/$17.00 PI1 SO379-6779(96)03894-5

0 1997

Elsevier

Science

S.A. All

rights

were

s-served

I

I

Cticde

Ana

RESBvdr

Fig. 1. Electrochemical synthesis

Experimental Aniline

prevent mixing of the anode and cathode compartment solutions. The anode consisted of a porous 1.1 cm thick, 2.8 cm disk of 100 PPI reticulated vitreous carbon (RVC) (ERG Materials and Aeros ace Corp) with an approximate surface area of 530 cm Y, The cathode consisted of a 3.8 cm thick, 2.8 cm diameter 100 PPI RVC disk with an approximate surface area of 1825 cm2.

R.?S3VW

flow-through

cell

for

colloid

Electrolyte solutions were pum ed through the RVC electrodes, within their respective ce K compartments, at 160 mL/min using a peristaltic ump. Synthesis was undertaken at +0.9OV vs Ag/AgCl Por a total of 90 minutes with periodic sampling of approximately 100 mL of the anode electrolyte/colloid solution at 30, 60 and 90 min. UVVisible (UV-Vis) spectra and circular dichroism (CD) spectra (Jobin Yvon Dichrograph 6) were taken of the sampled solutions at the time of sampling (time zero) and then at 1, 2, 4 and 24 hrs intervals after sampling. After 24 hrs the colloidal dispersions of polyaniline, collected at 30, 60 and 90 minutes, were coagulated by preparative

182

J.N. Bar&i

et al. /Synthetic

ultracentrifu 8 e (Beckman $timaTM LX!) at 49,000 3v-g; 1.5 hrs and en re-suspen ed m deiomsed water. and CD spectra were taken of these solutions as well as particle size analysis, zeta potential , cyclic voltammetry and colloid yield measurements performed. Results

Metals

84 (1997)

181-182

deviations are due to slightly concentrationson re-suspension.

different

colloid

and discussion

The electropolymerisation processwas monitored using UV-visible spectroscopy since this provides a nondestructive method for following the formation of either doped or undoped polymer, asshown in Figure 2. This data suggestthat a doped polyaniline colloid is obtained, with the “concentration’ increasing as a function of polymerisationtime.

‘.’ Tlil

450 510 Wavelength (nm)

1.0

r k,

0.0 -I 300

I 4w

500

600

Wavelength

700

800

900

(nm)

Fig. 2. UV-Vis spectraof PAn[(+)-HCSA/HCl] colloid growth at time = 5,30,60 & 90mins. CD spectra were also obtained for the samecolloidal samples.Samplesextracted at 30 mins showed no optical activity. On the other hand, samplestaken at 60 and 90 mins displayed increasing optical activity, respectively. Interestingly, theseCD bandsattributed to macromolecular asymmetry m the conducting lymer backbone increased upon standing, as shown in IFlgure 3. It therefore appears that the molecular rearrangementprocessinducin optical activity is much slower than the doping processitseBf. 10

T

630

Fig. 4. CD spectraof (+)- and (-)- HCSA PAn colloids (30,60 and 90min samples)re-suspendedin water.

SO mins 0.6

570

The colloid ield obtained for the re-suspended (+)HCSA samplesrl’ows a linear increasewith synthesistime up to 52 mg/g aniline after 1.5 hours. The yields observed are expressed as mass of colloid recovered after ultracentrifugation per gram of aniline in the electrolyte solution. Colloid particle size analysis (Malvern ZetaMaster PCS) indicated that the dispersion, after ultracentrifugation and re-dispersion in water resulted in particle aggregation, The particle size measured for the aggregate was a proximately 4 urn with a mean zeta potential of - 8 m9 . Conclusions

x

References

111

PI -15 4 330

390

450 510 Wavekngth (nm)

570

630

Fi .3. Ageing CD srtra of the 60 min sampleof PAn[(-)H&A] at 0,l and 2 s after sampling. After 24 hrs, both the PAn(+)-HCSA and PAn.(-)-HCSA enantiomers, were re-suspended in water after ultracentrifu to remove the excess(+)- or (-)-HCSA and their C ectra were recorded (Figure 4). These s ectra show t at the colloidal particles retain their cri lrality in the absence of excess HCSA and are approximate mirror images for each enantiomer. Slight

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