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The rheological behavior of semidilute galactomannan solutions in the presence of borax has been studied. The effects of polymer and borate concentrations, ionic strength, pH, and temperature are investigated and discussed. The shape of the viscoelastic functions of galactomannan–borax gels is similar to that for semidilute or concentrated polymer solutions. In 1 M NaCl, electrostatic effects are screened and the characteristic moduli of the gels appear to be determined by the number of interchain crosslinks. The elastic plateau modulus varies linearly with the free borate concentration and with the 2.6 power of the galactomannan concentration. Time–temperature type superposition is applicable if a vertical shift is introduced to account for the exothermic nature of the complexation reactions. Moreover, it seems possible to control the gel reversibility and the lifetime of crosslinks by changing the complexation kinetics via the pH.

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We have studied the complexation of ions in polymer solutions and argue that when complexation leads to the formation of intramolecular cross-links (2:1 complexes) the usual law of mass action scheme adequate for small molecules must be revised. This limits the use of potentiometric methods in studying polymer-ion complexation. UB NMR spectroscopy on a suitably chosen borate-polyhydroxy compound (poly(glyceryl methacrylate)) system enables us to determine the concentration of free borate 1:1 and 2:1 complexes in a saline solution and to compare with a model system. The concentration of 1:1 complexes seems to be proportional to the free ligand concentrations, as for small molecule complexation. However, the formation of 2:1 complexes from 1:1 complexes (dicomplexation step) in dilute polymer solutions seems to be essentially independent of the global ligand concentration, contrary to the situation in model systems. Only when interchain 2:1 complexes are formed (in semidilute regime), a ligand concentration dependence appears. The number of intrachain complexes could be governed by the local polymer properties, e.g., chain stiffness.

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