COMPARISON OF HYDRODYNAMIC AND RHEOLOGICAL PROPERTIES OF DILUTE-SOLUTIONS OF A STYRENE-HYDROGENATED BUTADIENE COPOLYMER IN ALIPHATIC SOLVENTS BY LIGHT-SCATTERING AND VISCOMETRIC TECHNIQUES

Dilute solutions Of a styrene-hydrogenated butadiene copolymer, a visc osity index improver, were studied by static and dynamic light-scatter ing techniques. In n-hexane (a model solvent for paraffinic oils) and a mineral base oil, aggregation is observed below 30-degrees-C. In cyc lohexane (a model solvent for napthenic oils) only isolated polymers a re present in the whole temperature range. Kinematic viscometric measu rements from 20 to 60-degrees-C in the mineral oil show a continuous i ncrease of the intrinsic viscosity together with a decrease of k(H), t he Huggins coefficient, from 2.5 to 0.5. At shear rates between 5000 a nd 40000 s-1, a large shear thinning is observed at room temperature f or the polymer in the mineral base oil. This effect progressively disa ppears as the temperature increases and the suspension becomes Newtoni an near 100-degrees-C. All results can be interpreted in terms of mice lle formation. (C) 1994 John Wiley & Sons, Inc.