Cluster phases

As the ion content of an ionomer increases, the proportion of the cluster phase to the multiplet-containing... 

Figure 1 (tan 5)max versus ion content for the multiplet phase and the cluster phase of Na-SPS ionomers. 

Studies of PMMA-based ionomers also demonstrate the influence of thermal treatment on deformation modes (16). For Na salts of PMMA-based ionomers of 6 and 12 mol% that were cast from DMF, only crazes were observed on straining. However, after an additional heat treatment (48 h at 160°C), which also removes any DMF solvent that is present, shear deformation zones are induced. Hence, the ionic cluster phase, which was destroyed by the polar solvent, has been restored by the heat treatment. 

The mechanical properties of ionomers are generally superior to those of the homopolymer or copolymer from which the ionomer has been synthesized. This is particularly so when the ion content is near to or above the critical value at which the ionic cluster phase becomes dominant over the multiplet-containing matrix phase. The greater strength and stability of such ionomers is a result of efficient ionic-type crosslinking and an enhanced entanglement strand density. 

A German saying goes You can t stand upright on one leg only . Looking at the achievements of John D. Corbett it is clear that his scientific body stands solidly on two legs Solid-state Zinfl compounds and centered cluster phases of early transition metals. 

Within the family of interstitially centered cluster phases the zirconium halides comprise a special field of materials, because it has been developed solely by J. D. Corbett and coworkers. This is truly Corbetts chemistry . 

Of course, the chemistry of zirconium cluster phases has been well described and reviewed in the literature [1-4]. Apart from a very few examples, mostly in the binary halides, almost all reduced zirconium halides contain octahedra of zirconium atoms centred on an interstitial atom Z. Several possible and experimentally realized Z include H, Be-N, K, Al-P, and the transition metals Mn-Ni. All these compounds have the general formula Ax"[(Zr6Z)Xi2X[J], with a " = alkali or alkaline earth metal cation, X=C1 Br or I, X =inner edge-bridging halide [5], X =outer exo-bonded halide, and 0[Pg.61]

Mixed-Chloride-lodide Zirconium Cluster Phases with a 6 12-Metal Halide Ratio 63 5.3... 

This structure type evidently requires the simultaneous existence of two differently sized halide types, and thus exists only in mixed hahde systems. Recent investigations revealed this cubic stracture also for cluster phases with other interstitial atoms, i.e., the cation-free Si-centered [(Zr6Si)Cli2-xl2+x] [28]. 

Fig. 5.17 View of the structure of the orthorhombic mixed-halide cluster phase Cs2[ Zr6B)CbT.98l3.02] showing the two types of cluster chains (thermal ellipsoids with 50% probability). Cs cations and inner halides are omitted for clarity.

Mixed Chloride-Iodide Zirconium Cluster Phases with a 6 18 Metal Halide Ratio -Products from Solid-state Reactions... 

A systematic study of this class of compounds did not start until twenty years later and led to the preparation of a series of M3Q7X4 (M = Mo, W Q = S, Se and X = C1, Br) inorganic polymers by high-temperature reactions (ca. 350 °C) of the elements in a sealed tube [10-14]. The interest on these cluster phases was mainly motivated by their excellent role as synthons for the preparation of molecular M3Q7 and M3Q4 cluster complexes, as will be presented in this section. 

The nature of the clustered phase is not well understood. One possible interpretation is that a cluster is composed of a relaxed divacancy whose inner surface is dressed with hydrogens however there is no direct NMR data which supports this identification (Reimer and Petrich, 1988). Alternatively, it has been suggested that the broad component of the NMR spectrum arises from hydrogen atoms lined up alone microtubular structural defects (Chenevas-Paule and Bourret, 1983). 

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