Determination of the weight-average molecular weight of polyamide-6 on the basis of melt viscosity

A theory of a two-point rheometrical method of determination of the weight-average molecular weightM _w of polyamide-6 is presented. The method is based on the measurement of the instantaneous values of zero-shear-rate viscosity of the degrading polymer melt, and a formula is derived which enables the calculation of the initial value ofM _w (i.e. at zero-residence-time in molten state) of the investigated sample. The experimental verification of the method proves its applicability. The considerations carried out may be regarded as a first step towards developing a theory of an in-line rheometer for a continuous determination ofM _w .