Macromolecular complex formation aqueous solution

Macromolecular Complex Formation and Polymer Adsorption on Colloidal Particles in Aqueous Solution... 

Macromolecular Complex Formation. The ultimate objective of the studies on complex formation between polymers in aqueous solution is to understand how the PEG chains interact with either the PMAA or PAA chains on the molecular level. For example, we would like to know whether... 

Unmodified poly(ethyleneimine) and poly(vinylpyrrolidinone) have also been used as polymeric ligands for complex formation with Rh(in), Pd(II), Ni(II), Pt(II) etc. aqueous solutions of these complexes catalyzed the hydrogenation of olefins, carbonyls, nitriles, aromatics etc. [94]. The products were separated by ultrafiltration while the water-soluble macromolecular catalysts were retained in the hydrogenation reactor. However, it is very likely, that during the preactivation with H2, nanosize metal particles were formed and the polymer-stabilized metal colloids [64,96] acted as catalysts in the hydrogenation of unsaturated substrates. 

The exchange reactions between salts of polymer adds (bases) and weak polybases (polyadds) in aqueous solutions are accompanied by considerable pH changes and also by the appearance of turbidity, particularly if the components are mixed in equivalent quantities. The copredpitation of polymeric adds and polybases was described first by Fuoss and Sadek This behavior of the mixture of two oppositely charged polyelectrolytes can be explained by the formation of a polyelectrolyte complex, this reaction being accompanied by elimination of a low-molecular weight acid or base. Thus, the exchange reaction between poly(acrylic add) and pdly(4-vinyl-ethylpyridinium bromide) was shown by potentiometry and turbidimetry to result in the precipitation of an insoluble macromolecular product, i.e. the ionic comj ex, and... 

The addition of water-soluble polymers followed by ultrafiltration, named as polyelectrol)de-enhanced ultrafiltration (PEUF), can be efficiently exploited to remove ionic species from aqueous solutions. This process is based on the use of a polyelectrol)de having an opposite charge to that of the target ions and the formation of macromolecular complexes between pollutant ions and polymer due to electrostatic attractions. These complexes are too large to pass through a UF membrane so they are retained in the retentate streams. Examples of separation of both cationic and anionic metal ions by PEUF have been extensively reported (Christian et al., 1995 Tabatabai et al, 1995a Tangvijitsri et al, 2002). 

As far as the excimer decay kinetics of PAA in aqueous media is concerned, de Melo and coworkers [122,130,131] have investigated the time-resolved fluorescence from a series of samples modified with various amounts of pyrene and naphthalene, respectively. Even when the aromatic content was as low as 2mol%, excimer formation was evident in the steady-state spectra. The fluorescence decays were complex irrespective of the label and were best modeled by a triple-exponential function (as in Eq. 2.8) both when emission was sampled in the monomer and excimer regions. In contrast to the distribution of rate constants in the blob model [133,134], the authors favored a scheme that describes the decay kinetics in terms of discrete rate constants. The data were also consistent with previous schemes [124-127] that account for the presence of two distinct types of monomer in addition to that of excimer in macromolecular systems one monomer enjoys kinetic isolation and is unable to form excimers, whereas the second is able to participate in excimer formation within its fluorescence lifetime. The authors [130] concluded from both steady-state and time-resolved data that PAA undergoes a conformational change from a compact form in acidic solution to an open coil at high pH. Furthermore, as the... 

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