Macroanions

For the anionic models, the detailed studies on their interactions with poly-and mononucleotides have not yet been carried out. However, we may say that the interactions of bases between the models and polynucleotides would be faint because of the strong electrostatic repulsive forces between the macroanions. 

The integral molar concentration of unassociated macroanions is A. The total cummulative molar... 

Steady State Population Density Distributions. Representative experimental population density distri-butions are presented by Figure 1 for two different levels of media viscosity. An excellent degree of theoretical (Equation 8) / experimental correlation is observed. Inasmuch as the slope of population density distribution at a specific degree of polymerization is proportional to the rate of propagation for that size macroanion, propagation rates are also observed to be independent of molecular weight. 

Fig. 11. (P6017N)7 cyclic macroanion forming the structural skeleton of... 

Qualitatively, the dipole-dipole interactions between the macro-molecular chains and the halide salt compensate for the lattice energy of the halide crystal and tend to decrease the interactions existing in the glass between the oxide macroanions. This decrease is probably the reason for the significant drop in the glass transition temperature resulting from the addition of a halide salt (Reggiani et al, 1978). Furthermore this type of reaction is consistent with the fact that dissolution of a halide salt in a vitreous solvent requires the existence of ionic bonds provided by a network modifier. 

No formal termination is given in structure 5.42 because in the absence of contaminants the product is a stable macroanion. Szwarz named such stable active species living polymers. These macroanions or macrocarbanions have been used to produce block copolymers such as Kraton. Kraton is an ABA block copolymer of styrene (A) and butadiene (B) (structure 5.43). Termination is brought about by addition of water, ethanol, carbon dioxide, or oxygen. 

Hving polymers Macroanions or macrocarbanions. macroions Charged polymer molecules. 

The most widely used chain reaction block copolymers are those prepared by the addition of a new monomer to a macroanion. AB and ABA block copolymers called Soprene and Kraton, respectively, are produced by the addition of butadiene to styryl macroanions or macrocarbanions (Equation 7.32). This copolymer is normally hydrogenated (Equation 7.33). 

Mora and coworkers201 studied the in vivo interaction, in mice, of toxic levels of cationic macromolecules with the carboxyl and sulfate derivatives of polyglucose. Toxic levels of polymyxin, protamine, streptomycin, and neomycin could be counteracted, if the synthetic macroanions were injected five to ten minutes after administration of the proteins. Subcutaneous administration of the anionic polyglucoses prior to intra-peri toneal injection of toxic levels of basic proteins afforded protection to the mice, and also demonstrated that the animals could survive, even when the two injections were by different routes. 

It appears that a combination of polymeric ions with difunctional initiators should be of some advantage over the transformation processes described above [241]. We have found that the combination of a macroanion with a dicationic initiator and of a macrocation with a dianionic initiator proceeds with high efficiency [242]. Macroions can therefore be transformed by difunctional initiators... 

An anionic active centre can be transformed to a radical centre by peroxy-alkyl halides [244] or by molecular oxygen [245], It appears, however, that the most elegant way so far was found by the British workers [246,247], They make use of the decomposition of unstable alkylsilver compounds generated from alkyllead salts and silver halides. The transformation thus proceeds in two steps. In the first step, a suitable Pb-containing end group is formed on the macroanion... 

This kind of transformation is mentioned in the patent literature [250]. After mixing with RLi or ROLi, 1-alkenes polymerizing on ZN catalysts yield macroanions of the poly(l-alkene). In the presence of a suitable monomer, a block copolymer is formed... 

The eliminated H+ terminates the attacking centre. In addition to the indicated reaction, the macroanions also attack completed chains so that isomerization and cross-linking result [50]. 

The compound consists of macroanionic chains (empirical formula [ZrP20ioH3] ), separated by NH4 cations. The octahedral Zr atoms are bridged with PO4 and HPO4 groups via Zr-O-P-O-Zr linkages. Thus each ZrOe octahedron shares four PO4 tetrahedra with each of its neighbors on either corner. 

Anionic polymerizations are generally much faster than free-radical reactions although the A p values are of the same order of magnitude for addition reactions of radicals and solvated anionic ion pairs (free macroanions react much faster). The concentration of radicals in free-radical polymerizations is usually about 10 -10 M while that of propagating ion pairs is 10 -10 M. As a result, anionic polymerizations are lO -lO times as fast as free-radical reactions at the same temperature. 

A variation of the sequential monomer addition technique described in Section 9.2.6(i) is used to make styrene-diene-styrene iriblock thermoplastic rubbers. Styrene is polymerized first, using butyl lithium initiator in a nonpolar solvent. Then, a mixture of styrene and the diene is added to the living polystyryl macroanion. The diene will polymerize first, because styrene anions initiate diene polymerization much faster than the reverse process. After the diene monomer is consumed, polystyrene forms the third block. The combination of Li initiation and a nonpolar solvent produces a high cis-1,4 content in the central polydiene block, as required for thermoplastic elastomer behavior. 

Two typra of methods were u d in the cationic polymerization of hetraocycles to determine the concentration of the Rowing species. The first type is based on methods used in free-radical polymerization (radical trapping) and in anionic polymerization when the macroanions are quantitatively converted into the stable end groups whose concentrations can then be measured. 

Other possible physiological functions of hyaluronic acid may be associated with its macroanionic nature. Aldrich (A4), for example, observed that Ca++ was strongly associated with a hyaluronic acid-protein complex, and was not readily displaced by high concentrations of univalent cations. A possible role for hyaluronic acid in regulating the concentrations of Na+ and K+ in nerve fibers has also been suggested (Al). 

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