Coordination crosslinks

The connection between polymer chemistry and ceramic science is found in the ways in which linear macromolecules can be converted into giant ultrastructure systems, in which the whole solid material comprises one giant molecule. This transformation can be accomplished in two ways—first by the formation of covalent, ionic, or coordinate crosslinks between polymer chains, and second, by the introduction of crystalline order. In the second approach, strong van der Waals forces within the crystalline domains confer rigidity and strength not unlike that found when covalent crosslinks are present. 

Coordination crosslinks were proposed, but not necessarily defined, by Agnew... 

Figure 4 Molecular model of nickel acetate dihydrate coordinated to two pyridine sidegroups in P4VP illustrating the concept of coordination crosslinks. This model is adopted from the geometry of nickel acetate tetrahydrate, based on its crystal structure. It is proposed that pyridine sidegroups in the polymer displace weak-base waters of hydration in the coordination sphere of the divalent nickel cation.

A simple coordination-interaction model is formulated that accounts for the disruption of coordination crosslinks and includes LFSEs for model complexes in the glassy and molten states. Both metal complexes have the same local symmetry (i.e., pseudo-octahedral) above and below die glass-transition temperature ... 

When ifickel coordinates to two pyridine ligands, there is no guarantee that these ligands reside on different macromolecular chains, producing effective crosslinks. Intramolecular loops form if both ligands originate from the same chain, and Tg should not increase much, if at aU, due to ineffective crosslinks. Hence p accounts for the fraction of effective intermolecular coordination crosslinks. 

The complex on the left side of the previous reaction simulates coordination crosslinks, where ligands in the sidegroup of the polymer occupy apical or equatorial sites in the first shell, and the complex on the right side represents a coordination pendant group. Typical models for the polymer in the previous dissociation reaction are as follows... 

The interaction of nanoparticles or clusters with traditional polymers improves the physicomechanical properties and performance of composites. Properties improve because particles form ionic and coordination crosslinks, restricting the mobility of polymer chains or their segments. Other cohesional and adhesional interactions also further restrict mobility. 

It should be noted extra-coordination processes are also important in controlling the properties of metallopolymers. Thus mechanical parameters and performance of many metal-containing polymers are determined by the ability of the metals to form ionic or coordination crosslinks (i.e., additional interchain interaction), and to exhibit cohesion and adhesion properties. Formally, unit variability in these cases is determined by the presence of metals in the chain with different coordination numbers. The incorporation of cluster-containing Os3-monomers into a polystyrene or poly(acrylonitrile) chain results in a mutual thermal stabilization of both the polymers and the clusters incorporated into the chains. These effects are observed only in cases where the cluster monomers are chemically bound to the polymeric chain. The influence of the chain may be manifested as the transfer of energy from the rotation-vibration degrees of freedom of the cluster to the translational degrees of freedom of the polymer chain segments at elevated temperatures. 

Gao ZQ, Binyamin G, Kim HH, Calabrese Barton S, Zhang YC, Heller A. Electrodeposition of redox polymers and co-electrodeposition of enzymes by coordinative crosslinking. Angew Chem Int Ed 2002 41 810-813. 

Heller A, Gao Z, Dequaire M. Electrodeposition of redox polymers and co-electro-deposition of enzymes by coordinative crosslinking. WIPO Pub No. 20030168338, 2003 (to TheraSense, Inc.). 

---