Matrix polyacetylenes

MATPAC, Novel Highly Polar Matrix Polyacetylenes [21, 22]... 

The high polar group tolerance of ylide nickel catalysts enables the polymerization of acetylene in polymer solutions not only of low polarity but also of medium and high polarity. These options provide synthetic access to a wide range of novel matrix polyacetylenes (MATPAC). Examples of polymers that may be used as matrix... 

Ostoja Starzewski, K. A., and Bayer, G. M., Polyacetylen in polyacrylnytril-matrix novel soluble matrix polyacetylene by ylide-nickel catalysis, Angew. Chem. Int. Ed. Engl, 30, 961-962 (1991). 

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. 

Impurity and Aperiodicity Effects in Polymers.—The presence of various impurity centres (cations and water in DNA, halogens in polyacetylenes, etc.) contributes basically to the physics of polymeric materials. Many polymers (like proteins or DNA) are, however, by their very nature aperiodic. The inclusion of these effects considerably complicates the electronic structure investigations both from the conceptual and computational points of view. We briefly mentioned earlier the theoretical possibilities of accounting for such effects. Apart from the simplest ones, periodic cluster calculations, virtual crystal approximation, and Dean s method in its simplest form, the application of these theoretical methods [the coherent potential approximation (CPA),103 Dean s method in its SCF form,51 the Hartree-Fock Green s matrix (resolvent) method, etc.] is a tedious work, usually necessitating more computational effort than the periodic calculations... 

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. 

Some of the innovative materials contain PAC in a highly dispersed heterogeneous distribution. Others are homogeneous and soluble. All of them can be processed by conventional techniques such as melt and blow extrusion, fiber spinning, film casting or spin coating. And some of them even provide the necessary matrix stabilization for turning polyacetylene into a useful material. 

The results are consistent with a model of polyacetylene sidechains on the matrix polymer backbone. While the mechanistic origin of the proposed graft reaction is unknown, a CH activation of a bond geminal to the polar substituent could explain the range of polymers accessible by this novel synthetic route. 

A polyacetylene membrane was first applied to mimic a presynaptlc membrane. An Ohmic contact was formed on the back side of a polyacetylene membrane. The potential of the polyacetylene was controlled with a potentlostat. In an acetonitrile solution containing acetyl choline, polyacetylene was found to be electrochemlcally reduced with resulting incorporation of acetyl choline Into the matrix. The polyacetylene membrane was Initially controlled at a potential to Incorporate the neurotransmitter. The neurotransmitter remained entrapped within the membrane matrix when the polyacetylene membrane was kept at a proper potential. Timed release of the neurotransmitter was performed with the polyacetylene membrane. When the polyacetylene membrane was stimulated by an electric pulse, the entrapped acetyl choline was released from the matrix (137). A graphite membrane showed properties similar to the polyacetylene membrane In the timed release of acetyl choline (140). 

A structural model, based on a complex process of stretch induced ordering in the polyacetylene domains, was proposed to account for these observations. Support for this model was obtained using electron microscopic techniques. Low polyacetylene content blends (<20% PA) were found to consist of discrete polyacetylene domains dispersed in a continuous polybutadiene matrix. In the high polyacetylene content blends (>70% PA), both phases were simultaneously continuous, forming an interpenetrating network structure. Blends with intermediate compositions consist of both continuous and isolated domains of polyacetylene distributed throughout the polybutadiene matrix. 

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. 

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