Polyelectrolyte polycation

A similar example is the formation of nonstoichiometric interpolymeric complexes between mutually complementary polyelectrolytes — polycation and polyanion [69,70], They behave like true polymer networks and are capable of swelling the interpolymeric complexes between PAAc and polyethylene piperazine swells, for instance, 16-18 times [70], Also advantageous in this case is the possibility to carry out this type of crosslinking in open systems, such as soil. 

Although the general picture can be drawn, several problems must be solved that arise from the interaction of polyelectrolytes (polycation and polyanion) with ions (MV2+ and EDTA). These interactions bring about changes in polymer chain configuration. This effect is manifested by the... 

FIGURE 4.8 Dipping methods using two different polyelectrolyte (polycation and polyanion) solutions to produce (a) single-sided and (b) double-sided modified membranes. 

Meisel etal. [18-20] were the first to investigate how the addition of a polyelectrolyte affects photoinduced ET reactions. They found that charge separation was enhanced as a result of the retardation of the back ET when poly(vinyl sulfate) was added to an aqueous reaction system consisting of tris(2,2 -bipyridine)ruthenium(II) chloride (cationic photoactive chromophore) and neutral electron acceptors [21]. More recently, Sassoon and Rabani [22] observed that the addition of polybrene (a polycation) had a significant effect on separating the photoinduced ET products in an aqueous solution containing cir-dicyano-bis(2,2 -bipyridine)ruthenium(II) (photoactive donor) and potassium hexacyano-ferrate(III) (acceptor). These findings are ascribable to the electrostatic potential of the added polyelectrolytes. 

The pioneering work on amphiphilic polyelectrolytes goes back to 1951, when Strauss et al. [25] first synthesized amphiphilic polycations by quaternization of poly(2-vinylpyridine) with n-dodecyl bromide. They revealed that the long alkyl side chains attached to partially quaternized poly(vinylpyridine)s tended to aggregate in aqueous solution so that the polymers assumed a compact conformation when the mole fraction of the hydrophobic side chains exceeded a certain critical value. Thus, Strauss et al. became the first to show experimentally the intramolecular micellation of amphiphilic polymers and the existence of a critical content of hydrophobic residues which may be compared to the critical micelle concentration of ordinary surfactants. They called such amphiphilic polyelectrolytes polysoaps [25],... 

Sassoon and Rabani [79] also prepared a two polymer system in which a chromophore was covalently bound to one polyelectrolyte and a donor or acceptor was electrostatically held by the other polyelectrolyte, and showed that its back ET underwent a similar retardation effect. They employed 26 as a photosensitizer, MV2+ as a mediator, and ferricyanide as an acceptor electrostatically bound to the added polycation (polybrene). 

As a polycation, chitosan spontaneously forms macromolecular complexes upon reaction with anionic polyelectrolytes. These complexes are generally water-insoluble and form hydrogels [90,91]. A variety of polyelectrolytes can be obtained by changing the chemical structure of component polymers, such as molecular weight, flexibility, fimctional group structure, charge density, hydrophilicity and hydrophobicity, stereoregularity, and compatibility, as... 

The penetration of ions from the subphase into the shell of spread particles is a general phenomenon and can be used to modify and functionalize the particle surface. For example, metal ions, such as Ba and Fe, or cationic polyelectrolytes, such as the polycation of polyallylamine, can be adsorbed at anionic particles, while anionic water-soluble dyes, such as phthalocyanine tetrasulfonic acid and 1.4-diketo-3.6-diphenylpyrrolo[3.4-c]pyrrole-4, 4 -disulfonic acid (DPPS) [157], can be adsorbed at cationic particles. However, since only a monolayer of the dye is adsorbed, a deep coloration of the particles is not obtained unless a dye with very high absorption coefficient is used [156],... 

Nonhomogenous distribution of charge inside fully condensed DNA/polycation particles has been discussed earlier, in Section lll.F.l. Since it takes only 0.9 equivalents of positive charges to condense DNA in aqueous environment, there should be an excess of positive charge on the surface of completely condensed DNA/polycation particles. This fact opens the opportunity to form multilayered structures based on alternations of polyelectrolytes of opposite charge. Details of this approach of DNA/polyion self-assembly are discussed in Section III.F.9. 

Solutions of polyelectrolytes contain polyions and the free (individual) counterions. The dissociation of a polyacid or its salt yields polyanions, and that of a polybase or its salt yields polycations, in addition to the simple counterions. The polyampholytes are amphoteric their dissociation yields polyions that have anionic and cationic functions in the same ion and often are called zwitterions (as in the case of amino acids having HjN and COO groups in the same molecule). Such an amphoter will behave as a base toward a stronger acid and as an acid toward a stronger base its solution properties (particularly its effective charge) will be pH dependent, and an isoelectric point (pH value) exists where anionic and cationic dissociation is balanced so that the polyion s charges add up to zero net charge (and solubility is minimal). 

The evaluation of each individual polyelectrolyte and binary polyanion-polycation pairs has followed the protocol described in Fig. 1. 

Typically, a binary system was selected as the base component of the recipe and the addition of polyelectrolytes to either side (core or receiving bath) was tested to evaluate the change in the capsule properties. The 33 successful multicomponent membrane systems are presented in Table 1. The components of the core material side (21 different chemical compositions) are listed in the first column, while the receiving bath components (20 different chemical compositions) are listed in the second column. With the exception of xanthan and CMC, the first polymer listed on the core side are gelling polymers which form beads with the appropriate ionotropic cation (salt). CMC can also be gelled by ions (alum), although they are considered to be non-compatible for cellular applications. The cations were tested both sequentially, usually with ionotropic cation first, and simultaneously. Walled capsules with adequate mechanical properties were often obtained through the simultaneous application of two polycations. Such a... 

Analysis by XPS after incorporation of the linear or dendritic cationic polymers showed an increase in the atom % N consistent with incorporation of an N-rich polycation. The polyvalent interactions between the cationic polyelectrolytes and the poly(sodium acrylate)graftson PE were stable to Soxhlet extraction with 95% ethanol, repeated acid/base treatment, and soaking or sonication in isopropanol and THE However, in these cases, simple acid treatment did not release the cationic polymer as was the case with PAA/Au grafts even though grafting in both cases was reportedly ionic and not covalent. 

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