Polymerization acetylenes

Catalysis research by Reppe et al. (1948) and Natta et al. (1958) initiated the search for a new material polyacetylene. It stimulated tremendous research effort worldwide, especially over the past two decades. Unhke contemporary developments for polyethylene and polypropylene, polyacetylene has yet to become a useful product. 

The original material (subsequently called URPAC) is accessible in various morphologies with a large number of Ziegler-Natta type and other transition metal catalysts. It has been studied in detail with spectroscopic and other physicochemical methods. Quantum theoretical model calculations have provided insights into the energetics of conjugated double bond systems. 

Material science interest focuses on potential applications of its specific electronic and band structure. Metal-like conductivities, semiconductor properties, photoconductivity and the nonlinear optical features of URPAC samples suggest devices for electromagnetic shielding, energy storage, microelectronics, optoelectronic and optooptical communication or optical computing. 

However, URPAC is a black, insoluble, infusible material which cannot be processed. The 3-dimensional crosslinking not only hinders the analytical polymer characterization. In addition, owing to the resulting lack of synthetic/catalytic 

Clearly, novel concepts for catalysts, changing the property profile, had to be developed to overcome these drawbacks. 

Tang and co-workers used leucine-functionalized phenyl acetylene derivatives for the construction of amphiphilic helical polymers, which were envisioned to be both semi-conducting and biocompatible, leading to diverse applications such as biosensors [36]. The polymerization was performed with a rhodium catalyst and resulted in high molecular weight polymers, particularly for polyacetylene la (1.5 10 g/mol). Interestingly, only the polymers in which the stereo-center was closely located to the helical backbone (la and lb) showed a CD signal and were optically active (Fig. 6). 

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Polymerization and GycliZation. Acetylene polymerizes at elevated temperatures and pressures which do not exceed the explosive decomposition point. Beyond this point, acetylene explosively decomposes to carbon and hydrogen. At 600—700°C and atmospheric pressure, benzene and other aromatics are formed from acetylene on heavy-metal catalysts. 

From the earliest days of radiation chemistry it has been known that acetylene polymerizes to a cuprene-like ( alprene ) solid (5, 6,25,28). The characteristics of the polymerization—e.g., lack of effect of temperature, doso rate, and pressure on polymer yield and negligible effect of radical scavengers—led Lind (24) to postulate an ion cluster mechanism. 

Anticipating the discussion on acetylene polymerization [98], extensively reported in Section IV, a value of n = 0.6 has been found, which implies a linear diffusion-controlled growth where the molecular librational and translational oscillations control the approach of the monomers to the active sites (chain terminations). 

Similarly, the addition of Ag in Pd-Ag alloy catalysts with Ag on the surface changes the selectivity in acetylene polymerization. 

Systematic studies of acetylene polymerization were conducted in the laboratories of the duPont Co and the results are described in numerous papers (see Ref 3). Studies of acetylenic polymers from the point of view of their utilization in solid rocket propeliancs has been conducted by Reaction Motors (see Ref 10). Polymerization under press is described in Ref 4 and some industrial products obtained by polymerizing acetylene are listed in Ref 5... 

Piganiol, New Industrial Acetylene Polymerization Derivatives," BuliFr 9,749-58 (1942) CA 38,3248( 1944) 6)N. Shimi zuya T.Kimura, JapanP 175,984(1948) CA... 

Disubstituted acetylenes, polymerization, 11, 566 Disubstituted ferrocenes, properties, 12, 227 a,a -Disubstituted olefins, ethylene co-polymerization,... 

Monoaromatic acetylenes, polymerization, 11, 566—568 Monoaryloxo complexes, with mono-Cp Ti(IV), 4, 474 Mono(benzamidinate) complexes, in ethylene polymerization, 4, 1139-1141... 

Synthesis of Cyclic Polymers Using Acetylene Polymerization. 143... 

Masuda, T., Acetylene Polymerization , in Catalysis in Precision Polymerisation, John Wiley Sons, Chichester-New York, 1997, pp. 67-97. 

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