RHEOLOGICAL PROPERTIES OF HYDROPHOBICALLY-MODIFIED ALKALI-SOLUBLE POLYMERS - EFFECTS OF ETHYLENE-OXIDE CHAIN-LENGTH

The rheological properties of hydrophobic alkali-soluble associative p olymers (HASE) were studied using control:led rats (Mettler LS40) and controlled stress (TA CSL 500) rheometers. The effects of pH and polym er concentrations on the rheological properties of three HASE model po lymer systems (i.e., HASE 5141, 5134, and 5142, with a degree of ethox ylation of 2.5, 10, and 40 mel, respectively) and a reference polymer without associative hydrophobes (MAAEA) were examined. As the pH is in creased by addition of ammonia to greater than 5-6. the carboxyl group s ionize to carboxylate ions and the polymers become water soluble. Th e HASE polymers thicken mainly by hydrophobic association. Viscosity c an increase by two to three orders of magnitude as pH is raised to 9. The degree of ethoxylation in the macromonomer controls the nature of the hydrophobic association junctions by altering the flexibility and hydrophobicity of the macromonomer. Optimum thickening efficiency is o bserved in the system with approximately 10 mol of an ethylene-oxide s pacer between the polymer backbone and the macromonomer. Viscoelastic study shows that the maximum thickening efficiency also corresponds to the dominant elastic property observed in the system with 10 mol of E O. All the model systems except the control system without hydrophobe exhibit strain thickening of the viscous and elastic components. (C) 1 998 John Wiley & Sons, Inc.