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 met hacrylate) - M(w)BAR = 1820 kg/mol - in the thermodynamically good sol vent toluene and in the theta solvent 2-propanol were measured up to p ressures of 2000 bar as a function of shear rate gamma in the temperat ure interval from 40 to 70-degrees-C. Both systems obey Graessley's eq uation so that it is possible to obtain the following rheological para meters in addition to the zero-shear viscosity eta0 from the dependenc es eta(gamma). Eta can be split into an entanglement part eta(ent) plu s a frictional contribution eta(fric), and the characteristic viscomet ric relaxation time tau0 becomes accessible. The present results demon strate that the application of pressure raises the above parameters mu ch less for good than for bad solvents. In contrast to eta(fric) (whic h 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 irres pective of the thermodynamic quality of the solvent. For the good solv ent the effects of temperature can be described by the Arrhenius equat ion, whereas the WLF equation has to be used for the bad one.