Polyacetylene polymer blends

The experimental procedure for the preparation of the-polyacetylene/styrene-diene triblock polymer blend was essentially the same as that of the EPDM/polyacetylene blend. The polyacetylene/styrene-diene triblock polymer was doped with either I2 or FeClg in nitromethane. 

Poly thiophene, PTP, and polypyrrole, PPR, blends with PS and PC were prepared by Wang et al. [1990] by thiophene or pyrrole electrochemical polymerization using electrodes coated with PS or PC hlms. The thiophene or pyrrole diffuses into the fihn and polymerizes in-situ in the film. Threshold conductivity occurs at 18 wt% for both conducting polymers in PS. Lower levels exist for PTP (12 wt%) and PPR (7 wt%) in PC. Miscibility of PPR/PC is attributed to the lower threshold limit as phase separated blends would be expected to have higher values. Previous studies with polyacetylene/PS blends reported threshold conductivity at 16 wt% polyacetylene [Aldissi and Bishop, 1985]. 

There are several approaches to the preparation of multicomponent materials, and the method utilized depends largely on the nature of the conductor used. In the case of polyacetylene blends, in situ polymerization of acetylene into a polymeric matrix has been a successful technique. A film of the matrix polymer is initially swelled in a solution of a typical Ziegler-Natta type initiator and, after washing, the impregnated swollen matrix is exposed to acetylene gas. Polymerization occurs as acetylene diffuses into the membrane. The composite material is then oxidatively doped to form a conductor. Low density polyethylene (136,137) and polybutadiene (138) have both been used in this manner. 

For silica in SBR, a polyacetylene coating gives the lowest filler-filler interaction, a good filler-polymer interaction, and the best dispersion compared to untreated and the other plasma-treated samples. However, for the stress-strain properties, the polythiophene-treated sample gives the best results. This shows the importance of sulfur moieties on the surface of the filler, which form a secondary network in the cured materials. In the blend of S-SBR and EPDM rubbers, the situation is less conclusive. The Payne effect, the bound rubber, and... 

Another approach to blending of polyacetylene with tough polymers is to form graft or block copolymers 280,281). Aldissi282) produced block copolymers by polymerizing acetylene at the ends of chains of anionic polyisoprene after conversion of... 

Suspensions of polyacetylene were prepared as burrs or fibers (46) by using a vanadium catalyst. When the solvent was removed, films of polyacetylene were formed with densities greater than that prepared by the Shirakawa method. These suspensions were mixed with various fillers to yield composite materials. Coatings were prepared by similar techniques. Blends of polypyrrole, polyacetylene, and phthalocyanines with thermoplastics were prepared (47) by using the compounding techniques typically used to disperse colorants and stabilizers in conventional thermoplastics. Materials with useful antistatic properties were obtained with conductivities from 10" to 10" S/cm. The blends were transparent and had colors characteristic of the conducting polymer. For example, plaques containing frans-polyacetylene had the characteristic violet color exhibited by thin films of solid trans-polyacetylene. 

It is possible, however, to blend these intrinsically brittle polymeric conductors with polymers that enhance their mechanical properties. In the case of polyacetylene, this has been accomplished by polymerizing acetylene gas in the presence of a suitable host polymer, (5-7) Since polyacetylene is actually grown in the matrix of the host polymer, and not simply physically dispersed, the resultant morphology of the polyblend (and, hence, the electrical and mechanical properties of the system) can be manipulated by adjusting the reaction conditions. In addition, by proper selection of the blending component, it is possible to further modify the properties of the polyblend by physical means. 

Blending of polyacetylene with polybutadiene provides an avenue for property enhancement as well as new approaches to structural studies. As the composition of the polyacetylene component is increased, an interpenetrating network of the polymer in the polybutadiene matrix evolves from a particulate distribution. The mechanical and electrical properties of these blends are very sensitive to the composition and the nature of the microstructure. The microstructure and the resulting electrical properties can be further influenced by stress induced ordering subsequent to doping. This effect is most dramatic for blends of intermediate composition. The properties of the blend both prior and subsequent to stretching are explained in terms of a proposed structural model. Direct evidence for this model has been provided in this paper based upon scanning and transmission electron microscopy. 

Samples containing more than 2% of sulfur did not pick up any iodine even after a 72-hour period. The completely saturated EPDM portions of the blend seem to prevent any iodine molecules from permeating into the polyacetylene moieties. In order to circumvent this problem, we have doped the blend with iodine prior to the crosslinking procedure. Subsequently, the doped material having a conductivity of 60 ft-1 cm-1 was reacted with sulfur monochloride in a toluene solution for 10 minutes. The color of the solution turned from pale yellow to dark red while the polymer film remained insoluble in the toluene solution. 

Common conductive polymers are polyacetylene, polyphenylene, poly-(phenylene sulfide), polypyrrole, and polyvinylcarbazole (123) (see Electrically CONDUCTIVE POLYMERS). A static-dissipative polymer based on a polyether copolymer has been announced (124). In general, electroconductive polymers have proven to be expensive and difficult to process. In most cases they are blended with another polymer to improve the processibility. Conductive polymers have met with limited commercial success. 

By contrast, the ECP must have conjugated rigid-rod macromolecules. Several such polymers show high electrical conductivity (usually after doping), viz. polyacetylene (PAc), polyaniline (PANI), polypyrrole (PPy), polyparaphenylenes (PPP), or poly-3-octyl thiophene (POT). The resins are expensive, difficult to process, brittle and affected by ambient moisture, thus blending is desirable. For uniaxially stretched fibers the percolation threshold is 1.8 vol%, hence low concentration of ECP (usually 5-6 vol%) provides sufficient phase co-continuity to ascertain conductivity similar to that of copper wires (see Table 1.79). 

Orientation of the polymer chains can be obtained by different methods. Highly oriented films of poly acetylene have been made by performing polymerization in a liquid crystal 11,2]. It has also been shown that it is possible to attain highly oriented films of polyacetylene 13] and poly(p-phenylene vinylene) [4] by stretching their precursors. Kaneto et al. 15] have oriented polythiophene by stretching a film, prepared electrochemically on In-Sn oxide (ITO)-coated poly(ethyleneterephthalate) films. The processability of the recently developed poly(3-alkylthiophenes) [6-8] makes this class of polymers suitable for stretching. Yoshino et al. [9] have shown that it is possible to orient poly(3-alkylthiophene), both as free-standing films and in a blend with an elastomer. 

The technique most widely used in university laboratories is (or has been) the polymerization in situ in the matrix polymer (cf as one of the earliest examples, polyacetylene in LDPE [54]). The disadvantage is that the monomer must be able to diffuse into the matrix, and so must the polymerization agent. Furthermore, there is no possibility of purifying the resulting product, either the resulting polymer, or the blend. Finally, such blends are not processable afterward without losing conductivity. 

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