VISCOSITY OF ETHYLENE TETRAFLUOROETHYLENE ALTERNATING COPOLYMERS

Low shear rate viscosity measurements of alternating copolymers of eth ylene and tetrafluoroethylene (PETFE) melts have been performed at dif ferent temperatures by using the centrifuge ball viscometer. The visco sity eta (Pa s) could be obtained with an empirical relation, a(c) = ( 4.29 +/- 0.08) x 10(2)(eta V-proportional to)(0.856 +/- 0.004) , With a(c) and V-proportional to being, respectively, the acceleration (g = 9.8 m s(-2)) and the terminal velocity (m s(-1)) of a stainless steel ball of 1.58 mm diameter moving in the polymer melt, which was flame s ealed in a horizontal cylindrical glass tube of 4.26 mm diameter. For the temperature dependence of the viscosity, an activation energy E(a) of 15.3 kcal mol(-1) was determined. The activation energy for PETFE is between 5.7-14.6 kcal mol(-1) for polyethylene (PE) and 18-36 kcal mol(-1) for tetrafluoroethylene (PTFE). A relationship between the zer o shear rate viscosity eta(0) (Pa s) and the molecular weight M(w) (g mol(-1)) of PETFE copolymer melts at 280 degrees C [eta(0) = (1.23 +/- 0.02) x 10(-16)(M(w))(3.43 +/- 0.06)] should permit us to determine t he molecular weight of PETFE with the centrifuge ball viscometer.