Properties of SP Networks

These characteristics are illustrated by studies on SP networks formed through the same van Koten type pincer coordination complexes described above. We focus the discussion on SPs formed from poly(4-vinylpyridine) (PVP) that is cross-linked in DMSO by bis(M(ll)-pincer) compounds 4a-d (Fig. 3.5 Yount et al. 2005a, 2005b). The same simple steric effect in the pincer alkylamino ligands is used. 

A comparison with cross-linker 4a proves the underlying dynamics are controlled by metal-ligand dissociation. Ligand exchange kinetics for 4a are substantially faster than for 4b but the association thermodynamics are very similar, and the effect of those kinetics is dramatic. At 5% cross-linker, the dynamic viscosity of lOOmgmL 4a-PVP is only 6.7 Pa s, a factor of 80 less than that of the isostmctural network 4b PVP. Although the association constants are not identical, the effect of the thermodynamics would be to increase the viscosity of 4a PVP relative to 4b PVP, the opposite direction of that observed. The kinetics dominate even the extent of cross-linking 5% 4a PVP is less viscous by a factor of 5 than is 2% 4b PVP. 

Experiments on SP networks formed from multiple types of cross-linkers show that the response to an applied stress occurs through sequential, individual 

Similar effects are observed in the G and for different mixtures of networks (including those with three different cross-linkers). In all cases, the frequency onsets and magnitudes of the transitions are anticipated by the behavior of networks with a single cross-linker. 

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