Conductive Polymer Blends

The incorporation of electrically conductive polymers (doped conjugated polymers) into non-conductive polymers to impart electrical conductivity has been demonstrated in a number of examples. Conjugated polymers shown below are generally non-conductive (semiconductive), but exhibit electrical conductivities often in excess of 1 S/cm with acid dopants, such as mineral acids (e.g., HCl, H2SO4), iodine, or organic acids such as dodecyl benzene sulfonic acid. 

Polythiophene Polypyrrole Polyphenylene Poly(phenylene vinylene) 

With the observation that anionic surfactants (such as dodecyl benzene sulfonic acid) (DBSA) could be employed as dopants for conjugated polymers, Heeger and coworkers [1090-1092] investigated blends containing polyaniline (PANI)-DBSA. This was an important discovery and the organic add doped PANI was thermoplastic and could be melt processed with insu- 

Conductive polymer or carbon black at blend interface 

The percolation of conductivity in carbon black modified blends of waterborne polyester polyurethane and waterborne polyether urethane was determined to be as low as 0.2 vol.% carbon black [1097]. Significant improvements in tensile strength with carbon black addition paralleled the conductivity results. A similar concept employing conductive carbon black in melt processed immiscible polymer blends noted low percolation concentration, due to concentration of carbon black at the interface between the polymer phases [1098, 1099]. At intermediate concentrations of polymer blend components, the interface comprises a continuous network as illustrated in Fig. 4.30. 

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Conducting Polymer Blends, Composites, and Colloids. Incorporation of conducting polymers into multicomponent systems allows the preparation of materials that are electroactive and also possess specific properties contributed by the other components. Dispersion of a conducting polymer into an insulating matrix can be accompHshed as either a miscible or phase-separated blend, a heterogeneous composite, or a coUoidaHy dispersed latex. When the conductor is present in sufftcientiy high composition, electron transport is possible. 

Nam, K. et al., Acid-Base Proton Conducting Polymer Blend Membrane, U.S. Patent Application 2003/0219640, November 27, 2003. 

Conducting polymer blends based upon polyaniline (PANI) are a new class of materials in which the percolation threshold for the onset of electrical conductivity can be reduced to volume fractions well below that required for classical percolation (16% by volume for globular conducting objects dispersed in an insulating matrix in three dimensions) [277,278], The origin of this remarkably low threshold for the onset of electrical conductivity is the self-assembled network morphology of the PANI poly blends, which forms during the course of liquid-liquid phase separation [61],... 

Extrusion of Polymer-1 containing monomer of Polymer-2, followed by post reaction to Polymer 2 (polyimides, electrically conductive polymer blends, reactive blends, e.g., with crosslinked elastomers), etc. 

Most polymers have high electrical resistivity, are inexpensive in comparison to other known insulating materials are heat resistant and sufficiently durable. Owing to their sensitivity to oxidation and solvents, they are frequentiy blended to generate better electrical insulating alloys. In the past two decades, there has been serious elfort to modify the electrical properties of polymers and their blends. The electrically conductive polymers can be broadly categorized as (i) electrostatic dissipating polymeric compositions, and (ii) electrically conductive polymer blends. Utracki has reviewed evolution of these materials [Utracki, 1998]. 

Electrically conducting polymer blends are also produced by blending another conducting polymer e.g., poly-3-octyl thiophene) with a matrix polymer e.g., PP, PVC, PS, PE, EVAc, PVC/ABS etc.) introducing a dopant e.g., iodine) [Kokkonen et al., 1994]. Several strategies were adopted in preparing ECPBs. In one example, polyaniline was blended with dodecylbenzene sulfonic acid, mixed with PS, PE or PP and then melt processed. In another case, polyaniline was mixed with protoning acid metallic salt. The conductive material was melt mixed with PE, PS, PP or ABS [Kama et al, 1994 a b]. 

The subject of polymer blends has been one of the primary areas in polymer science and technology over the past several decades. Judging from publications, patents, major university programs, Ph.D. thesis topics, it continues to maintain significant importance. This will continue, as there are a number of unsolved problems and opportunities. As new areas of interest develop in polymer science, polymer blend technology often becomes an important segment (e.g., electrically conducting polymer blends). 

Scanning electron microscopy (SEM) data for carbon-black compounds and conductive polymer blends [72c], supported by recent transmission electron microscopy (TEM) evaluations [79,80] (shown in Figure 11.39) were made, they also contradict the assumption of a statistical distribution. We find complete dispersion below the critical volume concentration (I) and a sudden stiucture formation ( branched flocculate chains ) at the critical volume concentration. This structural feature remains at higher concentrations. 

Wang H. L., Toppare L., and Fernandez J. E., Conducting polymer blends polythiophene and polypyrrole blends with polystyrene and poly (bisphenol A carbonate). 

M. Wei, J. Lee, B. Kang, and J. Mead, Preparation of core-sheath nanofibers from conducting polymer blends, Macromolec. Rapid Commun., 26, 1127-1132 (2005). 

N. E Colaneri, L. W. Schacklette, EMI Shielding Measurements of Conductive Polymer Blends. IEEE Trans. Instrum. Meas. 1992,41,291-297. 

Parveen Saini (PhD Thesis) Synthesis, Characterization and Evaluation of Conducting Polymer Blends and Composites for Microwave Shielding and Antistatic Application, 2012 (Copyright Indian Institute of Technology, New Delhi, India). 

A. J. Heeger, P. Smith, Y. Cao, Self-Assembled Networks of Conducting Polyaniline in Bulk Polymers A New Class of Conducting Polymer Blends. Macromol. Symp. 1995, 98, 859-859. 

C. Y. Yang, M. Reghu, A. ]. Heeger, Y. Cao, Thermcd Stabihty of Polycuuline Networks in Conducting Polymer Blends. Synth Met 1996,79,27-32. 

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