Carbonates, polymerization

G. M. Jenkins and K. Kawamura, Polymeric Carbons—Carbon Fiber, Glass, and Char., Cambridge University Press, New York, 1976, 178 pp. 

Polymerization. Carbon monoxide forms copolymers with ethylene and suitable vinyl compounds. No large-scale uses for the copolymers or their further reaction products such as polyalcohols and polyamines have been found (75). 

Jenkins, G.M. and Kawamura, K., Polymeric Carbons Carbon t ibre. Class, and Char, Cambridge University Press, Cambridge, 1976. 

It should be emphasized that the electrochemical carbonization proceeds, in contrast to all other common carbonization reactions (pyrolysis), already at the room temperature. This fact elucidates various surprising physicochemical properties of electrochemical carbon, such as extreme chemical reactivity and adsorption capacity, time-dependent electronic conductivity and optical spectra, as well as its very peculiar structure which actually matches the structure of the starting fluorocarbon chain. The electrochemical carbon is, therefore, obtained primarily in the form of linear polymeric carbon chains (polycumulene, polyyne), generally termed carbyne. This can be schematically depicted by the reaction ... 

II2/CO = 2 polymeric carbon with time on stream resulting in deactivation ... 

FIGURE 4.2 Representation of different carbon types on cobalt, (a) Atomic carbon/ surface carbide in a threefold hollow site, (b) CHX species located in threefold hollow sites, (c) Subsurface carbon lying in octahedral positions below the first layer of cobalt, (d) Cobalt carbide (Co2C) with an orthorhombic structure, (e) Polymeric carbon on a cobalt surface, (f) A sheet of graphene lying on a cobalt surface. The darker spheres represent carbon atoms in all the figures. 

Polymeric carbon refers to chains of carbon monomers (surface carbide) that are connected by covalent bonds. It has been shown recently47 that the barrier for C-C coupling on flat surfaces (1.22 eV) is half that for a step site (2.43 eV), and may indicate that the growth of these polymeric species is favored on terraces. Polymeric carbon may also refer to carbon chains that contain hydrogen. In the case of CO hydrogenation on ruthenium catalysts, polymeric carbon has been identified as a less reactive carbon that forms from polymerization of CHX and has an alkyl group structure.48... 

FIGURE 4.8 The correlation between polymeric carbon amount, as determined by TPO, with TOS for 20 wt% Co/A1203 catalysts taken from the slurry bubble column operated at realistic FTS conditions.73... 

From the work reported in literature it can be thus concluded that there will be various forms of carbonaceous species, which vary in reactivity, that exist on the catalyst or support during FTS. Some forms of this carbon are active (atomic surface carbide and CHX species) and even considered as intermediate species in FTS. However, it is also clear that especially during extended runs there may be a build up/transformation to less reactive forms of carbon (e.g., polymeric carbon). The amounts of these species may be small, but depending on their location, they may be responsible for a part of deactivation observed on cobalt-based FTS catalysts. The electronic interaction of carbon with the catalyst surface may also result in decreased activity. 

Co/A1203 catalysts that contain higher amounts of less reactive polymeric carbon not only exhibited enhanced deactivation when tested in FTS when compared to the fresh catalyst, but also showed an increase in selectivity to olefinic products.31 The authors postulated that this was probably due to the reduction in hydrogenation ability of the carbon deposited catalyst to convert primarily formed olefins into the corresponding paraffins. 

During conventional polymerizations of both HEMA and DEGDMA, complications resulting from diffusion limitations to termination and propagation are observed. Features such as autoacceleration, autodeceleration and incomplete conversion of double bonds characterize the rate behavior of these polymerizations. As TED is added to the reacting system, the carbon-DTC radical termination reaction is introduced. Diffusion limitations to carbon-DTC radical combination are lower than those to carbon-carbon radical termination as the DTC radical is smaller and much more mobile than a typical polymeric carbon radical. As a result, the cross-... 

For a review, see F. Diederich, Y. Rubin, Synthetic Approaches Towards Molecular and Polymeric Carbon Allotropes , Angew. Chem Int. Ed, Engl 1992, 31, 1101-1123. 

Y.-Z. An, Y. Rubin, C. Schaller, S. W. McElvany, Synthesis and Characterization of Diethynylmethanobuckmins-terfullerene, a Building Block for Macrocyclic and Polymeric Carbon Allotropes J. Org. Chem. 1994, 59, 2927-2929. 

Feng W, Bai XD, Lian YQ, Liang J, Wang XG, Yoshino K (2003). Well-aligned polyaniline/car-bon-nanotube composite films grown by in-situ aniline polymerization. Carbon 41 1551-1557. 

Despite the highly versatile application prohles of polymers with adjunct sucrose (or other sugar) residues—their major asset is enhanced hydrophUicity as compared to their hydrophobic petroleum-derived counterparts—interest appears to be restricted to biomedical uses. Currently none is produced commercially, as the generation of vinyl-sucroses and their often capricious polymerization have made their use as commodity plastics uneconomical. Another reason is their limited biodegradability only the sugar portion is biodegradable, with a polymeric carbon chain left over. Because biodegradability is a major issue today, " these polyvinylsaccharides are unlikely to become petrochemical substitution options in the near future. 

The structure of CO2-V has been determined by x-ray diffraction [343], and the observed pattern could be reasonably fitted by using a tridymite-type structure (orthorhombic P2 2 2 lattice) shown in Fig. 21. The formation and structure of polymeric carbon dioxide has been smdied by computational methods [344—348] in order to fuUy characterize this novel material however. 

Figure 21. Experimentally (trydimite) and theoretically (a-cristobalite) structures proposed for the polymeric carbon dioxide.

Continuous production of fullerenes was possible by pyrolysis of acetylene vapor in a radio-frequency induction heated cylinder of glassy polymeric carbon having multiple holes through which the gas mixture passes [44]. Fullerene production is seen at temperatures not exceeding 1500 K. The yield of fullerenes, however, generated by this method is less than 1%. A more efficient synthesis (up to 4.1% yield) was carried out in an inductively coupled radio-frequency thermal plasma reactor [45]. 

There may be occasions when it is difficult to decide whether a polymerization is anionic or cationic. The question can readily be resolved by the use of labelled quench agents (77, 78). In particular the use of a doubly labelled methanol (14CH3OT) will yield the information in one experiment. Thus, with anionic polymerization, tritium would combine with the polymer (Reaction 11) while with cationic polymerization, carbon-14 would be combined (Reaction 12). 

---