Non-stoichiometric Polyelectrolyte Complexes Research Articles

Behaviour of non-stoichiometric polyelectrolyte complexes in aqueous salt solutions

A study was made of the behaviour of dilute solutions of non-stoichiometric polyelectrolyte complexes in the presence of low molecular weight electrolytes in a wide range of concentration variation of these electrolytes. Using a number of systems it was shown that with an increase in the ionic strength of the solution a reduction was observed in the dimensions of polycomplex particles and second virial coefficients of their solutions. The molecular weight of polycomplex particles remained unchanged. On reaching a given salt concentration in the solution of the non-stoichiometric polycomplex, phase separation took place with a stoichiometric complex in the concentrated phase. It was shown that the ionic strength of the solution where particles of the polycomplex become insoluble is determined by a number of factors, first of all the chemical structure of individual polyelectrolytes forming the polycomplex and its composition. A study was made of the effect of the type of low molecular weight anion and cation on phase separation in solutions of polycomplexes. The behaviour of these solutions was examined using ionic strength I > 0·4 and it was shown that the complex breaks down to individual polyelectrolytes under these conditions; the system becomes single phase in the meantime. A system is proposed and described for physical and chemical conversions of particles of the polyelectrolyte complex in dilute solutions of low molecular weight salts.

Association and dissociation processes in solutions of non-stoichiometric polyelectrolyte complexes

A study was made of association and dissociation processes in solutions of nonstoichiometric water soluble poly-complexes. It was shown that the formation of associated particles in solutions of these poly-complexes is a general feature of these macromolecular compounds, which is independent of the type of polyelectrolyte contained in the poly-complex in excess. Association of particles of non-stoichiometric poly-complexes is due to intermolecular segregation of hydrophobic units consisting of double sequences of pairs of polyelectrolyte units forming salt bonds. The degree of association of non-stoichiometric poly-complexes is first of all determined by the ratio of hydrophobic and hydrophilic sequences of ionized polyelectrolyte groups contained in excess in the poly-complex, which do not form salt bonds (units) and secondly, by the state of hydrophilic units determined by interaction of ionized groups contained in excess in the poly-complex with low molecular weight counterious.

The structure of non-stoichiometric, water soluble polyelectrolyte complexes

Aqueous solutions of non-stoichiometric polyelectrolyte complexes (NSPELC), i.e. those in which one of the components is present as excess, have been examined. The NSPELC which are water soluble must be regarded as a new class of ionic polymers having a collection of fixed macromolecular characteristics, such as their mol. wt., particle size, and composition. The NSPELC particle can be visualized as a molecule of a specific block copolymer consisting of hydrophobic (a sequence of polyelectrolyte chain units forming a salt bond) and hydrophilic (sequence of ionized groups of the PEL present as excess but not forming salt bonds) blocks. The differing solubilities of these blocks in the solutions of the investigated polycomplexes cause their intramolecular seggregation, which stabilizes some conformation in the particle to be more compact than that of the individual polyelectrolytes (PEL).

Non-stoichiometric polyelectrolyte complexes: New, water soluble macromolecular compounds

Non-stoichiometri cpolyelectrolyte complexes (NSPELC) consisting of completely interacted polyelectrolyte pairs bearing opposite charges are examined. These are soluble in aqueous media, due to the presence of a sufficient number of free, ionized chain units which have not formed salt bonds between the chain, as a property. All the polyelectrolyte pairs are formed in the same way; it consists of mixing the two fully ionized compounds in the necessary proportions in the presence of a low mol. wt. salt. Where one of the components is present in excess and is a weak polyelectrolyte, water soluble NSPELC can be produced by titrating the incomplete reaction product with an acid or alkali until all the main chain units of the part present as excess are completely ionized. The molecular characteristics of the particles of such polyelectrolyte complexes (PELC) have been found to be independent of the synthesis method used. Proof of this is that the complex is present at an equilibrium.