Polyacetylenes mechanical properties

Coated materials are evaluated in S-SBR and in 50 50 blends of S-SBR and EPDM rubbers. In blends, the partitioning of fillers and curatives over the phases depends on differences in surface polarity. In S-SBR, polythiophene-modified silica has a strong positive effect on the mechanical properties because of a synergistic reaction of the sulfur-moieties in the polythiophene coating with the sulfur cure system. In S-SBR/EPDM blends, a coating of polyacetylene is most effective because of the chemical similarity of polyacetylene with EPDM. The effect of... 

Polyacetylene-modified sulfur is evaluated as a curative in a 50 50 blend of S-SBR/EPDM. In pure S-SBR, the mechanical properties decrease with the polyacetylene coating due to a reduced release rate of the sulfur out of its shell. The cure and mechanical properties of the S-SBR/EPDM blend are nearly doubled because of improved compatibility. 

This combination of high electrical conductivity and outstanding mechanical properties has been demonstrated for doped polyacetylene [3-6,28-30]. Unfortunately, since doped polyacetylene is not a stable material, the achievement of stable high performance conducting polymers remains an important goal. 

Experimental studies have established that for conducting polymers, the electrical properties and the mechanical properties improve together, in a correlated manner, as the degree of chain extension and chain alignment are improved. Polyacetylene remains the prototype example. 

The correlations between the electrical conductivity and the mechanical properties observed for polyacetylene are general. This correlation has been demonstrated in every case studied [27], and can be understood as a general feature of conducting polymers. 

In fact, for conjugated polymers, E results from a combination of a and tr bonds (the latter being equal to t ) and E,j is dominated by the interchain transfer integral, Thus, the inequalities imply that, quite generally, the conductivity and the mechanical properties will improve in a correlated manner as the degree of chain alignment is Increased. This prediction is in excellent agreement with data obtained from studies of the poly(3-alkylthiophenes), the poly(phenylene vinylenes), poly(thienylene vinylene) and polyacetylene [27]. 

Copolymers with longer polyene segments were found to be insoluble in the reaction solvent (toluene). In these materials, the polyacetylene fraction was crystalline (97). Copolymers with a low acetylene content were composed of a variety of isolated crystalline structures within an amorphous matrix, whereas those containing 50% or more polyacetylene had a morphology that resembled fibrillar polyacetylene. Dried copolymer solutions and suspensions gave blue films with the mechanical properties characteristic of the carrier polymer. No increase in environmental stability was observed. 

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. 

When acetylene gas is polymerized in a solid solution of the Shirakawa catalyst and polybutadiene, a heterogenous blend consisting of a amorphous polybutadiene phase and a crystalline polyacetylene phase is formed. (5) The mechanical and electrical properties of this composite are critically dependent on the composition of the blend components and on their relative arrangement. In our initial Blend paper, (5) for example, we showed that the mechanical properties of PA/PB blends are a function of the blend composition, with low polyacetylene compositions ex-... 

The high level of interest in potential applications of polyacetylene (1), (CH)X, is tempered in many instances by the prospects of intractability and poor physical and mechanical properties. In an attempt to mitigate such undesirable characteristics, we have attempted to prepare copolymers and blends (or composites) in which the electroactive component is (CH)X. 

This section concerns substituted polyacetylene film of formula CH = C[C6H4-o-Si(CH3)3] [111], The characteristics of the polymer are given in Table 5.3. A drop of a polymer solution in toluene at a concentration c = 3 X 10 gcm is deposited either on a mica surface or a lamellar structure. WSE2, then the solvent gently evaporates. As for a thin film, the mechanical properties can be a complex mixture of the rigidity of the film and of the substrate [112], the thickness of the polymer films was about or larger than 15 pm, such that the indentation depth h was always a small fraction of the thickness. 

Electrically conducting blends [29] of polyacetylene containing varying proportions of polybiitadiene (15%, 60% and 85%) were reported to have improved processability and mechanical properties, whereas electrical conductivities of the blends were observed to be 80, 15 and lOohm cm". Conducting blends degraded in air rapidly and blending did not show any... 

Well-known examples are polyliquid crystals [1]/ which have astonishing mechanical properties in the direction of orientation, and polyacetylenes, which when prepared without defects can be mechanically stretched up to 600 % and after doping give "metallic" conductivities of 100,000 S/cm [2]. 

Polyacetylene n. A polymer of acetylene, made with Ziegler-Natta catalysts and usually dark-colored, with the unusual property (for a polymer) of high electrical conductivity, achieved by doping the polymer with about 1% of ionic dopant such as iodine. It may become a useful solar-cell material because its absorption spectrum closely matches the solar spectrum, but mechanical properties and stability are poor. Also, practical processing methods have yet to be developed. 

With regards to the mechanical properties of substituted polyacetylenes, aromatic polymers like poly(diphenylacetylene) derivatives are generally hard and brittle, whereas aliphatic polymers with long alkyl chains like poly(2-octyne) are soft and ductile.Considerations of mechanical properties are especially important when polymer membranes or fibers are required for the specific application. 

A polymeric material that possesses the electronic, magnetic, electrical, and optical properties of a metal while retaining the processibility and mechanical properties usually associated with a conventional organic polymer is called a conducting pol ymer. Since the first demonstration of metallic conductivity in AsF5-doped polyacetylene by MacDiarmid and co-workers in 1977 [1], conducting polymers have become the main part of a larger class of materials commonly known as synthetic metals. 

TABLE 2 Comparison of Mechanical Properties, Stretchability, and Bulk Density of Polyacetylene Films... 

There are also other approaches to polymer stabilization (Aldiss 1989). For example, it was found that the formation of composites of two conducting polymers, one of which is air stable, improves the stability of polymer materials. Experiments carried out with pyrrole/polyacetylene and polyaniline/ polyacetylene composites have shown that the composites appeared to be more stable than doped polyacetylene and possessed mechanical properties similar to polyacetylene. Stabilization can also be achieved chemically by copolymerization. In particular, it was found that copolymerization of acetylene with other monomers such as styrene, isoprene, ethylene, or butadiene was accompanied by the increase of improvement of polymer stability (Aldiss 1989). Crispin et al. (2003) established that... 

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