Solvent-polymer complex, formation

There is eertainly strong experimental evidenee for the existenee of radieal-solvent eom-plexes. For instanee, Russelk and eo-workers eolleeted experimental evidenee for radi-eal-eomplex formation in studies of the photoehlorination of 2,3 -dimethylbutane in various solvents. In this work, different produets were obtained in aliphatie and aromatie solvents, and this was attributed to formation of a jr-eomplex between the Cl atom and the aromatie solvent. Complex formation was eonfirmed by flash photolysis. Complex formation was also proposed to explain experimental results for the addition of triehloromethane radieal to 3-phenylpropene and to 4-phenyl-1-butene and for hydrogen abstraetion of the t-butoxy radieal from 2,3-dimethylbutane. Furthermore, eomplexes between nitroxide radieals and a large number of aromatie solvents have been deteeted. Evidenee for eomplexes between polymer radieals and solvent moleeules was eolleeted by Flatada et al., in an analysis of initiator fragments from the polymerization of MMA-d with AIBN and BPO initiators. They diseovered that the ratio of disproportionation to eombination depended on the solvent, and interpreted this as evidenee for the formation of a polymer radieal-solvent eomplex that suppresses the disproportionation reaetion. 

In the absence of interaction between polymer and surfactant there are three contributions in the relative viscosity of the solutions those from the polymer, the surfactant micelles and the surfactant monomers, respectively. The contribution of surfactant monomers is negligible, but that of micelles may be relatively significant, especially in case of low molecular mass polymers. In order to interpret the conformational change of the polymer during complex formation, a consequent choice of the reference medium is of primary importance. Referring to polymer-free surfactant solution is unsuitable, because the surfactant solution has a different composition as a solvent with and without polymer. In a 25 mmoLkg" aqueous NaDS solution the micelles result in a 4% increase in... 

The formation mechanism of structure of the crosslinked copolymer in the presence of solvents described on the basis of the Flory-Huggins theory of polymer solutions has been considered by Dusek [1,2]. In accordance with the proposed thermodynamic model [3], the main factors affecting phase separation in the course of heterophase crosslinking polymerization are the thermodynamic quality of the solvent determined by Huggins constant x for the polymer-solvent system and the quantity of the crosslinking agent introduced (polyvinyl comonomers). The theory makes it possible to determine the critical degree of copolymerization at which phase separation takes place. The study of this phenomenon is complex also because the comonomers act as diluents. 

For example, the same dimer complex which contains two molar equivalents of ethanol, underwent photoreaction to give a higher molecular weight polymer (M = 12 000). The formation of such inclusion complexes with the solvent is rather generally observed with similar types of dimers formed with alcohols and some other solvents and, consequently, this enhances photopolymerizability. Such complex formation with a solvent may be one of the promising techniques that can be used for diolehn compounds in order to obtain polymers with high molecular weights. 

Special care has to be taken if the polymer is only soluble in a solvent mixture or if a certain property, e.g., a definite value of the second virial coefficient, needs to be adjusted by adding another solvent. In this case the analysis is complicated due to the different refractive indices of the solvent components [32]. In case of a binary solvent mixture we find, that formally Equation (42) is still valid. The refractive index increment needs to be replaced by an increment accounting for a complex formation of the polymer and the solvent mixture, when one of the solvents adsorbs preferentially on the polymer. Instead of measuring the true molar mass Mw the apparent molar mass Mapp is measured. How large the difference is depends on the difference between the refractive index increments ([dn/dc) — (dn/dc)A>0. (dn/dc)fl is the increment determined in the mixed solvents in osmotic equilibrium, while (dn/dc)A0 is determined for infinite dilution of the polymer in solvent A. For clarity we omitted the fixed parameters such as temperature, T, and pressure, p. 

The main classes of plasticizers for polymeric ISEs are defined by now and comprise lipophilic esters and ethers [90], The regular plasticizer content in polymeric membranes is up to 66% and its influence on the membrane properties cannot be neglected. Compatibility with the membrane polymer is an obvious prerequisite, but other plasticizer parameters must be taken into account, with polarity and lipophilicity as the most important ones. The nature of the plasticizer influences sensor selectivity and detection limits, but often the reasons are not straightforward. The specific solvation of ions by the plasticizer may influence the apparent ion-ionophore complex formation constants, as these may vary in different matrices. Ion-pair formation constants also depend on the solvent polarity, but in polymeric membranes such correlations are rather qualitative. Insufficient plasticizer lipophilicity may cause its leaching, which is especially undesired for in-vivo measurements, for microelectrodes and sensors working under flow conditions. Extension of plasticizer alkyl chains in order to enhance lipophilicity is only a partial problem solution, as it may lead to membrane component incompatibility. The concept of plasticizer-free membranes with active compounds, covalently attached to the polymer, has been intensively studied in recent years [91]. 

Anionic polymerization Initiated by electron transfer (e.g., sodium-naphthalene and styrene In THF) usually produces two-ended living polymers. Such species belong to a class of compounds called bolaform electrolytes (27) In which two Ions or Ion pairs are linked together by a chain of atoms. Depending on chain length, counterion end solvent, Intramolecular Ionic Interactions can occur which in turn may affect the dissociation of the ion pairs Into free ions or the llgand-lon pair complex formation constants. 

Generally, two different procedures have been adopted for preparation of MIPs. They involve either covalent or non-covalent complex formation of a template and complementary monomers with apt functional groups. [19]. Co-polymerization of this complex with a cross-linking monomer in a porogenic solvent solution, followed by removal of the template, results in formation of the porous polymer material with recognition sites complementary in size and shape to molecules of the target compound that can next be determined as an analyte. 

Poly(acrylhydroxamic acid)-Cu(II) complex has a high catalytic activity in the decomposition reaction of hydrogen peroxide. From the comparison of complex formation constants (stabilization constants) both in the polymer and the low molecular weight molecule, it was considered that the high activity is owed to a partly dissociated or a solvent coordinated moiety (104,105). Poly(methacryloylacetone)-Cu(II) complex is also investigated (108). 

While considering the rate-enhancing effect of bromobenzene in MMA polymerization initiated by AIBN, Henrici-Olive and Olive (19) noted that the effect can be explained as the consequence of electron donor—acceptor complex formation between polymer radicals and monomer or solvent molecules. Based on this view, these authors have shown that in polymerization in active solvents (which enhance the rate), the degree of polymerization Pn appears as a linear function of M2/Rp with... 

Proton-accepting polymers and proton-donating polymers typically interact with each other in aqueous medium and organic solvents almost stoichiometri-cally. This complex formation is affected by temperature, polymer structure, polymer concentration, solvent and other interaction forces, e.g. hydrophobic interactions. In general, the ratio [proton-accepting polymer units]/[proton-donating polymer units] in mol/1 of the complex is almost unity in dilute solu-... 

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