Transparency coordination polymers

While the alkali metal salts are water soluble, those of many other metals can be highly polymeric and insoluble in most solvents. These latter compounds are ionic coordination polymers of which a typical formula is [M (R2P02)2l , where M is a divalent metal such as Co, Zn, Be, Cu and R can be various combinations of alkyl and/or aryl groups. Their molecular weight can exceed 50,000 and they resist decomposition at temperatures up to SOO C. Some varieties form long flexible threads, while with suitable choice of R, the side group interactions can further modify the polymer properties. Some varieties which are soluble in organic solvents can produce transparent flexible Aims on evaporation. 

On the other hand, lanthanide ions are well known for their unique optical properties. These properties are extensively used in numerous fields such as laser amplifiers (Adam, 2002 Kuriki et al., 2002) or electroluminescent materials (Kido and Okamoto, 2002) for instance. Coordination polymers could be veiy interesting as far as optical properties are concerned. Indeed they are transparent and the rare earth ions distribution can be perfectly controlled by an appropriate choice of the ligand while in plastic or glasses they are generally statistically dispersed. The prerequisites of such coordination polymers exhibiting optical properties are obviously the following the material must be thermally rather stable, solvent molecules must be avoided and the inter-metallic distances must be carefully adjusted in order to allow the best efficiency for the targeted application. 

Remarkably, the aqueous solutions of the coordination polymers were shown to reversibly transform from transparent to translucent states above certain temperatures. At high temperatures, absorption spectra of coordination polymers were significantly... 

Mixed metal stabilizers are commonly used where more specialized applications (e.g. food contact) or specific properties (e.g. transparency) are requirements. These combinations of metal salts are chosen to balance the ability of their carbot late ligands to replace labile ehlorines on the ehain backbone and the resultant properties of the metal chlorides eventually formed. For example, a combination of barium-zinc stabilizer would be selected so that the chlorides end up as banum chloride, a weak Lewis acid, and the zinc compound coordinates strongly with the labile chlorine on the polymer chain, enabling its displacement. This rather simple stabilization reaction is further enhanced by the inclusion in these mixed metal stabilizers of chelating agents ... 

PMMA modified by inorganic nanoparticles such as Ti02, ZnS Mn, CdSe, CdSe/ZnS, ZnO, and CNTs has led to enhanced optical [16], thermal [149], and electrical properties, as compared to pure polymer. For example, Althues et al. [16] reported an efficient method for generation of completely transparent and strongly luminescent ZnS Mn/PMMA nanocomposites. They used in-situ bulk polymerization of transparent dispersions containing ZnS Mn nanoparticles in a mixture of MMA and AA the effective diameter of nanoparticles in the monomer dispersion was 22 nm. Two factors were responsible for the stability of the ZnS Mn/monomer dispersion, i.e., coordination of AA, which modified the surface of the nanoparticles and led to hydrophobization, and adsorption of ions leading to a surface charge... 

Copolymers of widely different monomers (e.g. Elvamide 8061 Du Pont) are also soluble in alcohols etc. because disorder in the polymer chain disrupts the formation of coordinated hydrogen bonds. Films formed from solutions dried at room temperature are usually opaque white and must be heated to 80°C to ensure transparency. The solutions gel at room temperature, so dissolve only by heating. These nylons suffer from the degradation reactions of the more common nylons. 

FIGURE 1 Dependence of transparency I of gradiently oriented film on h-coordinate (crossed Nichols) (a) Parallel clamps, the film of rectangle form, tension is perpendicular to the clamps, (b) Clamps allocated to the angle of 45° towards each other. Trapezium form Polymer film. The tension occurs in parallel to the base of trapezium, (c and d) Parallel clamps. Trapezium form Polymer fihn. Direction of tension is parallel to the attitude of trapezium. The length of one of free edges of the fihn (12) is more than the distance between clamps 11, and (e) Parallel clamps. Trapezium form Polymer film. Direction of tension is parallel to the attitude of trapezium. Relation 12 / the distance between two clamps are more for one film (case c) than that for another (case d). 

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