Ionicity Phillips

With the exception of LDPE, polyolefins like other polyethylenes and polypropylene, which represent the largest amount of vinyl-type polymers produced in the world, are neither synthesized by radical nor by classical ionic polymerisation processes. Different types of polymerisation catalysts are in use for these purposes. The Cr-based Phillips catalyst, Ziegler-Natta type catalysts, metallocene or other more recently discovered catalysts, including late transition metal catalysts, are all characterized by their propagation step where the olefin monomer inserts into a carbon-transition metal link. ... 

At present, the most widely used definition of fractional ionic character in solid state chemistry is that of Phillips (1970), based on a spectroscopic approach. Phillips defined fractional ionic character as... 

Jin, C.-M., Ye, C., Phillips, B.S., Zabinski, J.S., Liu, X., Liu, W., and Shreeve, J.M., Polyethylene glycol functionalized dicationic ionic liquids with alkyl or poly-fluoroalkyl substituents as high temperature lubricants,. Mater. Chem., 16, 1529-1535, 2006. 

Phillips (1973a) has proposed a new scale of ionicity for AB-type crystals based on the assumption that the average band gap. Eg, of these crystals consists of both covalent and ionic contributions as expressed by Eg = + Ef, where and , are the... 

The parameter is obtained by relating the static dielectric constant to Eg and taking in such crystals to be proportional to a - where a is the lattice constant. Phillips parameters for a few crystals are listed in Table 1.4. Phillips has shown that all crystals with a/ below the critical value of0.785 possess the tetrahedral diamond (or wurtzite) structure when f > 0.785, six-fold coordination (rocksalt structure) is favoured. Pauling s ionicity scale also makes such structural predictions, but Phillips scale is more universal. Accordingly, MgS (f = 0.786) shows a borderline behaviour. Cohesive energies of tetrahedrally coordinated semiconductors have been calculated making use... 

Table 1.4. Phillips Pauling ionicity parameters for some A B crystals...

Figure 1.4 Actual structures of alkali halides compared with the predictions of the ionic model. The figure is divided into three regions by lines corresponding to rjr = 0.414 and 0.732. The regions correspond to four-, six- and eight-coordinated structures. Filled circles denote six-coordinated structures, open circle, six- or eight-coordinated structure and filled squares, eight-coordinated structures. Note that the predictions of the ionic model do not entirely correspond with the actual structures of alkali halides (Following Phillips, 1973f>).

A not unrelated definition of a for sp-valent octet AB compounds has been given by Phillips and Van Vechten (1969). These octet compounds such as NaCl and ZnS have eight valence s and p electrons per AB unit Phillips and Van Vechten assumed that the average energy gap E% of these semiconducting or insulating compounds is made up of covalent and ionic contributions, Ec and E respectively, that are related via eqn (3.20) by... 

Thus as we go across the isoelectronic series Ge - GaAs -> ZnSe - CuBr, the degree of ionicity increases from 0 -> 0.32 -> 0.56 - 0.71 as expected. A noteable achievement of the Phillips-Van Vechten ionicity scale was that it also allowed an excellent structural ordering of the sp-valent octet compounds. As shown in Fig. 3.4, the structure map ( c, E ) separates all those... 

Fig. 3.4 The Phiilips-Van Vechten structure map ( c, ) for the sp-valent octet AB compounds. The four-fold coordinated zinc blende and wurtzite structure types are separated from the six-fold coordinated NaCI structure type by the straight line corresponding to the degree of ionicity a = 0.785. (After Phillips and Van Vechten (1969).)...

There is a small break in slope after gadolinium in some plotted ionic radii, notably for octahe-drally coordinated cations, attributed to crystal field effects on electrons in the 4/orbitals. This is discussed in Phillips Williams (1966, vol. 2, p. 106). 

Pioneering work in fibroin wet spinning can be traced back to 1930s. After that, little work has been done until the late 1980s, when more research was done to investigate the spinning dope systems, and structure and properties of the artificial fibroin silk. The composition of the dope is very important to the properties of the final fiber. Several kinds of solvents, such as LiBr—EtOH, Ca(NOo,)2—MeOH, formic acid, HFIP, hexafluoro acetone (HFA), and so on, are used to prepare the spinning dope (Table 4). Very recently, an ionic liquid was used as dope solvent (Phillips et al., 2005). 

Gupta, M.K., Khokhar, S.K., Phillips, D.M., Sowards, L.A., Drummy, L.F., Kadakia, M.P., and Naik, R.R. "Patterned silk films cast from ionic liquid solubilized fibroin as scaffolds for cell growth". Langmuir 23(3), 1315-1319 (2007). 

Phillips, D.M., Drummy, L.F., Naik, R.R., Trulove, P.C., De Long, H.C., and Mantz, R.A. "Silk regeneration with ionic liquids". Abstracts of Papers of the American Chemical Society... 

Fig. 2. Plots testing simple ionic model equations for diatomic molecules in the gas phase, ionic crystals and the hydration of ions. The slopes of the lines coincide with those of the simple theory, see Phillips and Williams. U is the binding energy from free gas ions.

Phillips and Williams (16) have proposed a general method of noting thermodynamic evidence for deviation from the ionic model presuming the latter to be closely followed by all IA and IIA cations. 

Evangelou, V. P. and R. E. Phillips. 1984. Ionic composition of pyritic coal spoil leachate. Interactions and effect on saturated hydraulic conductivity. Reclam. Reveg. Res. 3 65-76. 

Modifications have recently been proposed for the Dimersol and the Phillips processes by Institut Frangais du Petrol and Sasol Technologies, respectively, based on the use of an ionic liquid such as imidazolium tetra-chloroaluminate (Figure 17), which is liquid at room temperature and an excellent solvent for the organometallic catalyst. 

The ionic liquid can, for example, be added to the butene effluent from the Dimersol process to obtain octenes by butene dimerization the octene can be carbonylated (Section 4.6) and hydrogenated to wo-nonanol, used to make phthalate plasticizers. In the case of the Phillips trimerization process the use of an ionic liquid allows an easy separation of the trimers and the catalyst for recycling (see also reviews to Section 5.5). However, the industrial use as solvents of ionic liquids, containing halide species (especially anions such as Bp4, PFg, or AlCU ) has the disadvantage that they readily break down to give HX, which can adversely affect the reaction. New types of non-halide containing ionic liquids are being actively researched. 

We may note in passing that the dependence upon covalcncy from the Harrison-Phillips model, a,. — 0.5, does not look very similar to the present a, but does give a reasonable account of experiment. In fact, both arc approximately linear in p over the range of values of that occur. As we have noted about ionicity theories, a finding of linear plots is not compelling evidence for the validity of a model, particularly if a scale parameter is available. 

In addition to the reinterpretation of Pauling s rules developed by Burdett and McLarnan (1984), there have been a number of other studies related to various aspects of these standard rules. Due to the substantial number of errors in classifying AB compounds in terms of ionic radius ratio (e.g., Phillips, 1970 Tossell, 1980b), there have been numerous attempts to create structure maps that have two atomic quantities as coordinates and that can provide a unique separation of the different structure types. Such atom quantities may be related primarily to size or energy or to some combination of the two. Some of the most important such approaches are those of Mooser and Pearson (1959), Phillips (1970), and Simons and Bloch (1973). 

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