Polymeric solutions complexity

Often times concentrated polymeric solutions cannot be treated as Newtonian fluids, however, and this tends to offset the simplifications which result from the creeping flow approximation and the fact that the boundaries are well defined. The complex rheological behavior of polymeric solutions and melts requires that nonlinear constitutive equations, such as Eqs. (l)-(5), be used (White and Metzner, 1963) ... 

Palladium dichloride forms polymeric carhonyl complexes when the dry chloride is heated in a stream of carhon monoxide charged with methane vapor. Such complexes include [PdCl2(CO)n] and [PdCl(CO)2]n. The reaction also occurs in aqueous phase resulting in decolorization of the solution. 

A number of mechanisms proposed to explain the stereospecificity in polymerizations involve complexing of the monomer to a metal prior to addition to the chain (2). Kinetic evidence has shown that such a mechanism does occur with n-BuMgBr, n-BujMg and s-BuMgBr in THF-toluene solution. These polymerizations follow an internal zero-order rate equation. Bateup (1,8) proposed that the mechanism is... 

The pre-polymerization solution was analysed by measuring the absorbance of the template and monomers separately. These results were compared to the resulting spectra of a solution containing both the monomer and template. In another example [32] this approach has been used to confirm the interactions between MAA and 4-L-phenylalanylamino-pyridine. A UV-vis spectroscopy study has shown the increase in absorbance of the band corresponding to the template Umax - 245 nm) upon increasing concentration of the functional monomer. The data were also used as an indication of the formation of a 1 2 template monomer complex. The final polymer obtained was highly enantioselective. 

Up to now no rigorous quantitative theory describing the kinetics of homopolymerization even of one monomer is available within the framework of modern theory of polymeric solutions. The theory concerning copolymerization will become more complex since the rate constant of a pair of the macroradical recombination could depend not only on their degrees of polymerization but also on the composition and chemical structure of these macroradicals. 

One can differentiate two main methods for obtaining polymer-polymer complexes 1) formation of complexes from pre-existing chemically and structurally complementary macromolecules 2) polymerization of monomers in the presence of matrix macromolecules introduced in the reaction media. Such matrix polymerization is accompanied by the formation of polymer complexes. In the first case, the chemical reaction proceeds via complex formation by random contacts between reacting chains. Then, these sequences of pairs of connected chains grow. In matrix polymerization, the complex is formed by the mechanism of consecutive addition of monomer along the chain leading to the formation of the so-called zip-up (double-stranded) structure, due to matrix control of polymerization. One can expect that the various mechanisms lead to the formation of complexes with a different structure and properties. Indeed, a difference in the composition and properties of complexes obtained by various methods has been found So, the comparison of complexes poly(methacry-lic acid)-poly(2-N,N-dimethylaminoethyl methacrylate), obtained by mixing of equimolar quantities of components in solution and also by the matrix polymerization of dimethylaminoethyl methacrylate in water in the presence of PMAA, shows a difference in composition. In the first case, the content of acid in the complex is always... 

To what extent do the solution complexes formed between the monomer and the template in solution reflect the architecture of the polymeric binding sites This question is important, since a thorough characterisation of the monomer-template assemblies may assist in deducing the structure of the binding sites in the polymer and thus have a predictive value. 

Niobium occurs in oxidation state (V) in the dissolver solution and does not extract into pure TBP/OK phases to a significant extent. Values of ca. 5x10 have been quoted for Dn6 between 20% TBP/OK and 2 M HNO3. Inextractable polymeric hydroxy complexes of Nb are formed but the presence of silicates or HDBP can lead to some extraction of niobium species. A model for the extraction by HDBP is provided by HELP, which was thought to extract Nb according to equation (159) on the basis of IR studies. HDBP might similarly lead to some synergic extraction of Nb " in TBP/OK but, as mentioned above, free HDBP will not be available in the first process cycle,and in practice problems do not usually arise with niobium. 

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