M. Aldissi

Colloidal dispersions of conducting polymers

We have demonstrated that these same conducting polymers may be processed in aqueous media by chemical grafting or the physical adsorption of polymeric surfactants onto the conducting polymer chain/particle. Conditions for obtaining good dispersions have been shown to consist of oxidant/stabilizer compatibility, an appropriate number of active sites for adsorption or grafting of the appropriate surfactant and an appropriate molecular weight for the surfactant to assume sufficient coverage on the conducting core

Preparation and characterization of colloidal dispersions of polypyrrole using poly(2-vinyl pyridine)-based steric stabilizers

Abstract We describe the preparation of novel colloidal dispersions of polypyrrole in aqueous media via a dispersion polymerization route. Particle aggregation is prevented by a steric stabilization mechanism due to the adsorption of a tailor-made poly(2-vinyl pyridine-co-butyl methacrylate) (P2VP-BM) random copolymer onto the sub-micrometre polypyrrole nuclei. The particle morphology is spherical, as evidenced by transmission electron microscopy, and the average particle diameter could be controlled over the range 130–200 nm by varying the initial P2VP-BM concentration. The adsorbed mass of P2VP-BM per unit mass of polypyrrole was estimated indirectly using Fourier transform infrared spectroscopy. Compressed pellet conductivities of the freeze-dried dispersions were in the range 1–2S cm−1, despite the presence of the outer layer of adsorbed, insulating stabilizer surrounding each polypyrrole particle. Spin-coating experiments yielded films of similar conductivity and indicate that these polypyrrole dispersions represent a significant improvement in processability over bulk polypyrrole powders. Finally, the base-induced aggregation behaviour of these polypyrrole dispersions was studied with respect to particle concentration and solution pH. Differences between the present system and the poly(4-vinyl pyridine-co-butyl methacrylate)-stabilized polypyrrole dispersion previously investigated are qualitatively explained.

Poly(vinyl pyridine)-based stabilizers for aqueous polypyrrole latices

Abstract The preparation and characterization of sub-micronic polypyrrole latex particles using polymeric stabilizers based on poly(vinyl pyridine) is described. These novel colloidal dispersions enhance the usually limited processability of the electroactive component, and in addition exhibit usefully high solid-state conductivity (∼ 2 Scm −1 ), despite the presence of the insulating stabilizer component. Furthermore, these latices exhibit reversible base/acid induced flocculation-stabilization behavior. The latter phenomenon is of fundamental interest and is expected to have commercial applications. The latices were characterized by transmission electron microscopy, visible absorption spectroscopy. F.T.I.R. and Raman spectroscopy, microanalysis, and compressed pellet d.c. conductivity. Base-induced particle flocculation was studied as a function of latex particle concentration.

Synthesis and Characterization of Aqueous Colloidal Dispersions of Poly(Vinyl Alcohol)/Polyaniline Particles

Abstract Colloidal polyaniline has been prepared in acidic aqueous media by a modified chemical polymerization of aniline in the presence of a tailor-made polymeric surfactant. The surfactant which acts as a steric stabilizer used in this study is derivatized poly(vinyl alcohol-co-vinyl acetate). This surfactant contains pendant aniline units which participate in the aniline polymerization, resulting in the formation of sterically-stabilized polyaniline particles which have a non-spherical “rice-grain” morphology. It is shown that this novel form of polyaniline is more processable than the bulk powder that is normally obtained from a conventional chemical synthesis. The solid-state conductivity of solution-cast films or compressed pellets of these dispersions is surprisingly high (≃1 S/cm), despite the presence of the insulating outer layer of chemically-grafted stabilizer. We have characterized these polyaniline colloids by a wide range of techniques including electron microscopy, cyclic voltammetry and ...

Polyacetylene block copolymers

Abstract Block copolymers of polystyrene/polyacetylene, polyisoprene/polyacetylene and polyethylene/polyacetylene have been synthesized via an anionic to Ziegler-Natta catalysis in which the molecular weight of the anionic polymer is well controlled. The live chains are reacted with Ti(OBu)4, resulting in an alkylated titanium derivative, which after proper aging initiates the polymerization of acetylene, thereby forming the copolymers. Three different types of copolymers have been synthesized: (1) short anionic chains — non-soluble copolymer films (conducting); (2) medium length anionic chains — soluble copolymers (conducting); (3) long anionic chains — soluble copolymers (insulating).

Synthesis of highly conducting polystyrene-polyacetylene copolymers

Abstract Polystyrene-polyacetylene block copolymers were synthesized, via an anionic-to-Ziegler-Natta catalysis, where the amount of polystyrene in the copolymer is well controlled by controlling the monomer concentration at a fixed anionic catalyst concentration. The iodine doped films of the copolymers exhibit very interesting electrical properties, and their electrical conductivities are in the metallic regime for a ratio of polystyrene copolymer ⩽20% . This can be understood as a percolation phenomena supporting a variable range hopping transport mechanism in metallic polyacetylene.

Particle size distributions of polypyrrole colloids

Abstract We describe a new technique to determine the particle size distributions of sterically stabilized polypyrrole colloids based on a charge-velocity analysis (CVA). The size distributions of polypyrrole colloids prepared with various steric stabilizers have been examined and compared to the particle sizes obtained by conventional transmission electron microscopy techniques. It is shown that the CVA technique is particularly useful for the analysis of larger particle diameters (> 100 nm) and bi- or trimodal size distributions.

Potassium iodate oxidation route to polyaniline: an optimization study

Abstract A study of the bulk polymerization of aniline by potassium iodate in aqueous acidic media is reported. The effect of varying the solution acidity, reaction time and both the relative and absolute reactant concentrations on the polymer yield, chemical composition and compressed pellet conductivity of the polyaniline product was investigated. It is shown that substantial amounts of iodine are incorporated into the polymer, particularly at higher initial oxidant/monomer mole ratios. The chemical nature of the incorporated iodine species is complex but preliminary X-ray photoelectron spectroscopy studies suggest that several species are probably present. Partial removal of this iodine can be achieved by dedoping the polyaniline powders, indicating that at least some of the iodine is present as a dopant anion. The polyaniline powders were also characterized by scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and Raman spectroscopy.

Non-aqueous polypyrrole colloids: Synthesis and characterization

Abstract The preparation of sterically-stabilized polypyrrole colloids via a dispersion polymerization route in non-aqueous media is described for the first time. Pyrrole polymerization was achieved using FeCl 3 as an oxidant/dopant in organic solvents such as methyl acetate, methyl formate and propyl formate. Macroscopic precipitation was prevented by the use of poly(vinyl acetate) as a polymeric surfactant. Various other surfactants were ineffective and consequently resulted in precipitation of polypyrrole. Several techniques were used for characterization of the dispersions including transmission and scanning electron microscopies (TEM and SEM), thermogravimetric analysis (TGA), charge velocity analysis and visible absorption spectroscopy. TEM indicated a polydisperse spherical morphology with a particle diameter in the range 100–300 nm. The compressed pellet conductivities of the dried dispersion were as high as 0.1 S/cm. These dispersions are often compared with bulk and colloidal polypyrrole prepared in aqueous media.

Review of the synthesis of polyacetylene and its stabilization to ambient atmosphere

Abstract Two main topics in the field of polyacetylene are discussed. The first is the polymerization reaction, including the mechanism, the various catalytic systems with their selectivity and activity and the polymer morphology. The second is the polymer stability in ambient conditions, including the oxidation mechanism and the methods that are used or could be used for its stabilization.