Support materials other than polystyrene

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at - 20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects 54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3d ic activity, in view of the current interest in polymer-supported catalysts (51). 

Oxidation of waste plastics, such as polyethylene, polypropylene, polystyrene, poly (alkyl acrylates), and nylon 6,6, with NO/O2 for 16 h at 170°C, led to mixtures of carboxylic acids, for which uses would have to be developed if this method was applied to large volumes of waste plastics.180 Hydrogenation of polyethylene at 150C>C for 10 h over a sil-ica/alumina-supported zirconium hydride catalysts gave a 100% conversion to saturated oligomers.181 Polypropylene gave a 40% conversion to lower alkanes at 190°C for 15 h. It is not clear what use these materials would have, other than serving as a feedstock for a petroleum refinery. 

Another limitation that is specific to the parallel plate electrospinning technique is the collection of extremely thin nanofibers, which have been observed to break because they were unable to sustain the forces of their own weight and of the repulsive charges from other fibers [62]. An electrically resistive substrate inserted into the gap between the plates can provide support to fibers suspended between the plates without influencing fiber quality [62], and may also help to shield any conductive materials below the air gap, which may attract unwanted non-aligned nanofibers. Substrates with bulk resistivity greater than 10 Q cm, such as quartz and polystyrene, are suitable for placement between parallel electrodes, while materials with bulk resistivity of less than 10 Q cm, such as glass, may result in random fiber orientations [67, 68]. 

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