PRESSURE AND SOLVENT INFLUENCES ON THE SHEAR THINNING BEHAVIOR OF MODERATELY CONCENTRATED-SOLUTIONS OF POLY(BUTYL METHACRYLATE)

The viscosities of moderately concentrated solutions of poly(butyl methacrylate) - M(w)BAR = 1820 kg/mol - in the thermodynamically good solvent toluene and in the theta solvent 2-propanol were measured up to pressures of 2000 bar as a function of shear rate gamma in the temperature interval from 40 to 70-degrees-C. Both systems obey Graessley's equation so that it is possible to obtain the following rheological parameters in addition to the zero-shear viscosity eta0 from the dependences eta(gamma). Eta can be split into an entanglement part eta(ent) plus a frictional contribution eta(fric), and the characteristic viscometric relaxation time tau0 becomes accessible. The present results demonstrate that the application of pressure raises the above parameters much less for good than for bad solvents. In contrast to eta(fric) (which can react differently to the application of pressure due to special circumstances) eta0 and tau0 are always influenced to the same degree as T or p are changed. This result implies that the steady state shear compliance (tau0/eta0) is independent of the variables of state irrespective of the thermodynamic quality of the solvent. For the good solvent the effects of temperature can be described by the Arrhenius equation, whereas the WLF equation has to be used for the bad one.