Langmuir 1995,11, 4222-4224
4222
Synthesis of Colloidal Polypyrrole Particles Using Reactive Polymeric Stabilizers M. R. Simmons, P. A. Chaloner, and S. P. Armes* School of Chemistry and Molecular Sciences, University of Sussex, Falmer, Brighton, B N l 9QJ, U.K. Received July 17, 1995@ We describe, for the first time, the use of tailor-made reactive polymeric stabilizers for the synthesis of polypyrrole colloids. Using a poly(2-(dimethylamino)ethylmethacrylate-stat-3-vinylthiophene) stabilizer, the polypyrrole particles had diameters of approximately 100n m , contained 19wt % stabilizer, and exhibited solid-state conductivities as high as 4 S cm-l.
Introduction Polypyrrole is a relatively air-stable organic conducting polymer which suffers from poor processability. Since 1986 numerous workers have described the synthesis of sterically stabilized polypyrrole particles via dispersion polymerization, usually in aqueous These dispersions are significantly more processable than conventional polypyrrole bulk powders or films. The various polymeric stabilizers used to prevent macroscopic precipitation have generally been commercially available, and there have been relatively few attempts made to design tailor-made stabilizer^.^-^ In all cases the stabilizer is merely physically adsorbed onto the surface of the polypyrrole particles. In contrast, a wide range ofreactive copolymer stabilizers ( u s u a l l y containingpendant aniline g r o u p s ) have been reported for the preparation of polyaniline ~ o l l o i d s . ~In~this - ~ ~report we describe, for the first time, the synthesis of polypyrrole particles using tailormade reactive copolymer stabilizers based on poly(2(dimethylaminolethy1 methacrylate).
* To whom correspondence should be addressed. Abstract published in Advance ACS Abstracts, November 1, 1995. (1)See, for example, the Proceedings of the 1992 International Conference on Synthetic Metals (ICSM '92),Synth. Met. 1993,55-57. (2)Bjorklund, R. B.; Liedberg, B. J . Chem. SOC.,Chem. Commun. 1986,1293. (3)Armes, S.P.; Vincent, B. J . Chem. Soc., Chem. Commun. 1987, 288. Armes, S. P.; Miller, J. F.; Vincent, B. J . Colloid Interface Sci. 1987,118,410. (4)(a) Cawdery, N.; Obey, T. M.; Vincent, B. J. Chem. Soc., Chem. Commun. 1988,1189. (b) Epron, F.; Henry, F.; Sagnes, 0.Makromol. Chem., Mucromol. Symp. 1990,35136,527.(c) Odegard, R.;Skotheim, T. A.; Lee, H. S. J . Electrochem. Soc. 1991,138,2930.(d) Digar, M. L.; Bhattacharyya, S. N.; Mandal, B. M. J. Chem. Soc., Chem. Commun. 1992,18. (5)(a) Armes, S.P.; Aldissi, M.; Agnew, S. F. Synth. Met. 1989,28, 837. (b)Armes, S.P.; Aldissi, M.; Idzorek, G. C.; Keaton, P. W.; Rowton, L. J.; Stradling, G.; Collopy, M. T.; McColl, D. B. J . Colloid Interface Sci. 1991,141,119. (6)(a)Armes, S.P.;Aldissi,M.Synth.Met. 1990,37,137.(b)Beaman, M.; Armes, S. P. Colloid Polym. Sci. 1993,271(l),70. (7)Armes, S.P.;Aldissi, M. Polymer 1990,31, 569. ( 8 ) Beadle, P. M.; Rowan, L.; Mykytiuk, J.;Billingham, N. C.; Armes, S. P. Polymer 1993,34, 1561. (9)Arca, E.; Cao, T.; Webber, S. E.; Munk, P. Polym. Prepr. (Am. Chem. SOC.,Diu. Polym. Chem.) 1994,35 (11,334. (10)Armes, S.P.; Aldissi, M. J . Chem. Soc., Chem. Commun. 1989, @
88.
(11)Vincent, B.; Waterson, J. J . Chem. SOC.,Chem. Commun. 1990, 683. Aldissi, M.; Agnew, S. F.; Gottesfeld, S. Langmuir (12)Armes, S.P.; 1990,6, 1745. (13)(a)Liu, J.-M.;Yang,S.C . J . Chem. Soc., Chem. Commun. 1991, 1529. (b)Gospodinova, N.; Mokreva, P.; Terlemezyan, L. J.Chem. Soc., Chem. Commun. 1992,923. ( c ) Gospodinova, N.; Terlemezyan, L.; Mokreva, P.; Stejskal, J.; Kratochvil, P. Eur. Polym. J . 1993,29,1305. (d) Stejskal, J.; Kratochvil, P.; Gospodinova, N.; Terlemezyan, L.; Mokreva, P. Polym. Int. 1993,32,401. (14)DeArmitt, C.; Armes, S. P. J . Colloid Interface Sci. 1992,150, 134.
0743-746319512411-4222$09.00/0
It is well-known that alkyl substitution ofthe thiophene ring system lowers its oxidation potential with respect to electrochemical p~lymerization.'~Furthermore, the oxidation potentials of 2,2'-bithiopheneand pyrrole are quite similar: recently it has been shown that copolymerizing these two comonomers can give a "hybrid" conducting copolymer.16 Thus there appears to be good literature evidencethat polymerized, alkyl-substituted( b i l t h i o p h e n e groups should be effective graft sites for the in situ polymerization of pyrrole. Work by both Fernandez and co-workers and Stankeet al. suggeststhat pendant pyrrolic groups should also be ~uitab1e.l~ However, in our experience such pyrrolic groups seem to be rather prone to aerial oxidation; their use will be discussed in a future publication.18 Experimental Section The copolymer stabilizers were synthesized via the free-radical copolymerization of 2-(dimethylamino)ethyl methacrylate with 2-vinylthiophene, 3-vinylthiophene, 5-vinyl-2,2'-vinylbithiophene, or 2,Y-bithienylmethyl methacrylate (each of these (bi)thiophenebased monomers w a s synthesized according to known literature procedure^^^^^^) using AIBN in toluene at 70 "C. The comonomer feed ratio w a s typically 1O:l in favor of t h e 2-(dimethylamino)ethyl methacrylate comonomer. The resulting copolymers were purified by precipitation into n-hexane. The dried copolymers contained 7-15 mol % (bi)thiophene-based comonomer as assessed by IH NMR spectroscopy and C H N S elemental microanalyses. GPC analyses indicated polydispersities of 1.52.5 and M, values of 10 000-32 000 (PMMA standards, THF eluent, R I detector). The polypyrrole colloids were synthesized as follows (seeFigure 1):pyrrole (1.00 m L ) w a s added to an aged (0-30 m i n at room temperature), stirred aqueous solution (100 mL) containing the reactive copolymer stabilizer (1.00 g) and FeC13 oxidant (5.80 g). The solution turned black within a few seconds and w a s stirred at room temperature for at least 16 h. The resulting black dispersion w a s centrifuged at 40 000 r p m for 1-2 h , t h e colored s u p e r n a t a n t w a s carefully decanted, and the black sediment w a s redispersed in water using an ultrasonics bath. This centrifugation-redispersion cycle w a s repeated twice to ensure the complete (15)Waltman, R. J.; Diaz,A. F.;Bargon, J.J.Electrochem.Soc. 1984, 131 (6),1452. (16)(a) Peters, E.M.; Van Dyke, J. D. J . Polym. Sci., Polym. Chem. 1991,29,1379. (b) Liang, Q.Y.; Neoh, K. G.; Kang, E. T.; Tan, K. L.; Wong, H. K. Eur. Polym. J . 1992,28(7),755. (17)(a) Finzi, C.; Fernandez, J . E.; Randazzo, M.; Toppare, L. Macromolecules 1992,25, 245. (b) Stanke, D.; Hallensleben, M. L.; Toppare, L. Synth. Met. 1992,72 (11,89. (18)Simmons, M.; Chaloner, P. A.; Armes, S. P. Manuscript in preparation. (19)(a)Trumbo, D. L. J . Polym. Sci., Polym. Chem. 1988,26,3127. (b) Trumbo, D. L. J . Polym. Sci., Polym. Chem. 1991,29,603. (20)(a) Trumbo, D. L. Polym. Bull. 1988, 19, 217. (b) Wei, Y.; Hariharan, R.; Bakthavatchalam, R. J. Chem. SOC., Chem. Commun. 1993,1160.
0 1995 American Chemical Society
Letters
Langmuir, Vol. 11, No.11, 1995 4223
Water-solu hle rcactivc stabiliscr containing pcndant (hi)thiophcnc groups
(I)
Adti 0xid;int
1
Activation of pcndant thiophcnc graft sitcs
Results and Discussion Each of the three reactive copolymers containing 3-vinylthiophene, 5-vinyl-2,Y-bithiopheneor 2,2’-bithienylmethyl methacrylate pendant groups proved to be effective steric stabilizers for polypyrrole. On the other hand, the 2-vinylthiophene-based copolymer failed to prevent macroscopicprecipitation. The reason(s) for this unexpected anomaly are unknown at present. A typical transmission electron micrograph of the polypyrrole colloids is shown in Figure 2. The polypyrrole particles have a relatively monodisperse, spherical morphology, and the number-average particle diameter is approximately 100 nm. At higher magnifications there is some evidence for internal structure within these particles. Infrared spectroscopic studies on the dried colloids (KBr disk) revealed a strong polypyrrole signature, with an additional small carbonyl peak a t ca. 1720 cm-l due to the grafted copolymer stabilizer. The nitrogen microanalytical contents for the poly(2-(dimethylamino)ethyl methacrylate-stat-3-vinylthiophene)stabilizer, the resulting polypyrrole colloid, and a polypyrrole bulk powder prepared in the absence of this stabilizer were 8.27%, 14.84%, and 16.39%, respectively. Thus we estimate a stabilizer content of 19 wt % for this particular polypyrrole colloid. Room temperature solid-state conductivities of pressed pellets made from the dried dispersions were in the range 0.1-4 S cm-l. Preliminary visible absorption experiments provide some evidence for the postulated stabilizer-grafting mechanism. Evolution of an absorbance peak (Amm = 686 nm) is observed in aged poly(2-(dimethy1amino)ethyl methacrylate-stat-2,2’-bithienylmethyl methacrylate) stabilizer-oxidantsolutions (same reagent concentrationsbut in the absence of pyrrole monomer) which we attribute to the oxidative activation of the pendant bithiophene groups. Thus we believe that these oxidized bithiophene groups act as initiation sites for the in situ pyrrole polymerization, inevitably leading to stabilizer grafting onto the growing polypyrrole particles. We emphasize that no peak at 686 nm was observed for poly(2-(dimethylamino)ethyl methacrylate) homopolymer-oxidant solutions in our control experiments. Furthermore, subsequent addition of pyr1*6bp8
(ii) Add I’yrrolc
In situ polymcrisation
Stcrically-stabilised polypyrrole particles
Chcmically-grafted stcric stahiliser
Figure 1. Schematic representation of the synthesis of polypyrrole colloidsvia aqueous dispersion polymerization using statistical copolymer stabilizers which contain reactive (bi)thiophene groups. removal of inorganic by-products and excess, nongraRed copolymer stabilizer.
Figure 2. A typical transmission electron micrograph of polypyrrole particles synthesized using poly(2-(dimethylamino)ethyl methacrylate-stat-3-vinylthiophene) as a reactive copolymer stabilizer.
4224 Langmuir, Vol. 11, No. 11, 1995 role monomer to these latter solutions resulted only in quantitative precipitation of the conducting polymer, with no discernible colloid formation. We conclude that, for this particular stabilizer, the pendant (bilthiophene graft sites are essential for effective steric stabilization of the polypyrrole particles. Although we have focused on poly(2-(dimethylamino)ethyl methacrylate)-basedstabilizers in the present study, we believe that the “reactivestabilizer’’ route to polypyrrole colloids described here is very general. In principle, this new approach should allow polypyrrole colloids to be synthesized using polymeric stabilizers based on a much wider range of comonomers than presently used ( e g . , (methlacrylamide, 4-styrenesulfonic acid, (meth)acrylic acid, etc.1. Our preliminary experiments have confirmed that carboxylated polypyrrole particles can also be synthesized using the reactive stabilizer route if the pyrrole monomer is replaced with pyrrole-3-acetic acid. Potential applications for such dispersions include their use as novel marker particles for immunodiagnostic a ~ s a y s . ~ Here l-~~ the ability to incorporate functionality into the tailor-made
Letters stabilizers ( e g g amine ., or carboxylicacid groups as specific binding sites for the biological molecules of interest) is likely to be beneficial in minimizing the ubiquitous nonspecific binding effects which normally plague such assays. Furthermore, chemical grafting of the functional steric stabilizer to the surface of the polypyrrole particles should lead to more robust assays.
Acknowledgment. M.S. wishes to thank the EPSRC for a Ph.D. studentship. We thank Synthetic Chemicals Ltd. for CASE support. LA950590S (21) Tarcha, P.J.;Misun, D.; Wong, M.; Donovan, J. J. In Polymer Latexes: Preparation, Characterization and Applications; Daniels, E. S., Sudol, E. D., El-Aassar, M. S. Eds.; ACS Symposium Series 492; American Chemical Society: Washington, DC, 1992; Vol. 22, p 347. (22) Kawaguchi, H.Microspheres for Diagnosis and Bioseparation. In Polymer Materials for Bioanalysis and Bioseparation; Tsuruta, T., Hayashi, T., Kataoka, K., Ishihara, K., Kimura, Y., Eds.; CRC Press: London, 1993; p 294. (23) (a)Armes, S.P.; Maeda, S. Polym. P r e p . (Am. Chem. SOC., Diu. Polym. Chem.) 1994,35 (11,217. (b)Maeda, S.;Corradi, R.; Armes, S. P. Macromolecules 1995,28, 2905.
