Carbon-Hydrogen-Type Polymers

In addition, carbon-hydrogen bonds are present, particularly in carbonaceous materials obtained by carbonizing polymers at low temperatures, typically <1000 °C. Detailed discussions on the types of surface groups and their surface concentrations are presented by Boehm (14] and Rivin [15],... 

The hydrogenation of unsaturated polymers and copolymers in the presence of a catalyst offers a potentially useful method for improving and optimizing the mechanical and chemical resistance properties of diene type polymers and copolymers. Several studies have been published describing results of physical and chemical testing of saturated diene polymers such as polybutadiene and nitrile-butadiene rubber (1-5). These reports indicate that one of the ways to overcome the weaknesses of diene polymers, especially nitrile-butadiene rubber vulcanizate, is by the hydrogenation of carbon-carbon double bonds without the transformation of other functional unsaturation such as nitrile or styrene. 

As we will see, some anomalies in the isotopic composition of carbon, hydrogen and oxygen can be explained on the basis of this assumption, and we will start the discussion with the deuterium-rich matter in carbonaceous chondrites. This deuterium-rich matter is essentially present as complex macromolecules 70 73 96 97). The carbon in these samples is essentially normal 76,98). For some polymer-type fractions, the deuterium content is up to 32 times higher than the galactic value (D/H 2 x 10s in the number of atoms per cubic centimeter). High deuterium enrichments are known in interstellar molecules and the mechanism of this enrichment is fully understood. For an excellent review dealing with interstellar chemistry, see the paper by Winnewisser 99) and the previously mentioned book by Duley and Williams 13). 

Fluorocarbon polymers are the most resistant to this type of degradation because the carbon-fluoride bond is extremely stable, with an energy on the order of 116 kcal/mole, compared to carbon-hydrogen bond energies of 91-98 kcal/mole (3., ). Fluorocarbons are, however, extremely expensive because the monomers are more complicated to synthesize and more dangerous to handle. The polymers cost on the order of 10-20 per pound compared with the most widely used hydrocarbon polymers which can be 1-5 per pound. 

The concept of SI L catalyst has been developed quickly in the last decade. Holderich et al. [4] added acidic chloroaluminate ILs to various types of supports, and the catalytic activities of the immobilized ILs were found to be higher than those of the conventional catalysts under the same conditions. Inspired by this work, SIL catalysts have been widely used in the coupling reactions for olefin hydroformylation [5], olefin metathesis [6], Heck reactions [7], and hydroamination [8], and so on. SIL catalytic systems have also been reported for some other reactions, such as water-gas shift reaction [9], dihydroxylation of olefins [10], and hydrogenation [1 Ij. The solid supports used include magnetic NPs [12], mesoporous molecular sieves [13], soluble organic ions [14], noncovalently solid-phase [15], IL-functionalized carbon nanotubes [16], polymer cocktail [17], and so on. 

Carbon NMR in solution is the method of choice for many types of material characterisation. While the sensitivity is much lower than for protons (Table 3.1), synthetic polymers are often soluble at concentrations as high as 5-20 wt%, so C-NMR spectra with a high signal-to-noise ratio can be acquired in a few hours. One major advantage of carbon NMR is that the chemical shifts are dispersed over 200 ppm rather than the 10 ppm typically observed for protons [1]. In addition, C-NMR is frequently used to study polymer molecular dynamics because the relaxation is predominantly due to carbon-hydrogen dipolar interactions with directly bonded protons. The C-H distances are fixed by the bond lengths, so the relaxation times can be used to measure the rotational correlation times directly (eqn (3.4)). 

---