Relaxation spectrum calculation methods and their use to determine the molecular mass distribution of propylene, ethylene and α-olefin random copolymers

In the present study a nonlinear regression with regularization and inverse Fourier transformation methods were developed to determine the relaxation spectrum from the frequency-dependent storage and loss modulus data. The spectra obtained were used for the determination of the molecular mass distribution in a calculation process developed by D.W. Mead [(1994) Journal of Rheology 38 1797]. The molecular mass distributions of propylene–α-olefin and ethylene–α-olefin random copolymers have been determined by rheological and gel permeation chromatography methods and the distributions obtained by the two methods agreed quite well with each other.