SHEAR THICKENING OF HALATO-TELECHELIC POLYMERS IN APOLAR SOLVENTS

Short-length polymers selectively end-capped with a metal carboxylato group at both ends, i.e, metal carboxylato-telechelic polymers, exhibit an unusual shear-thickening behaviour in apolar solvents, depending on the main experimental parameters that control the ion-pair association, such as metal cation, concentration and temperature. In contrast to the non-ionic precursors, metal carboxylato-telechelics are indeed responsible for a marked increase in the solution viscosity in a range of shear rates between 0.1 and 1000 s(-1). The shear-rate dependence of the solution viscosity has been analysed in a close relationship to metal counterion, polymer concentration, temperature and addition of polar compounds to the apolar solvent. As a rule, the dilatant behaviour depends strongly on the formation of polymer aggregates in relation to the mutual interactions of the ion pairs. A consensus is now emerging on the origin of the shear-thickening effect, which should be found in inter-aggregate associations rather than in a transition from intramolecular to intermolecular associations of the individual chains.