A RHEOLOGICAL EVALUATION OF LINEAR AND BRANCHED CONTROLLED-RHEOLOGY POLYPROPYLENES

Commodity linear and branched polypropylene resins have been modified by means of peroxide initiated chemical degradation in a reactive extr usion process. Data collected from molar mass and linear viscoelastic property measurements have been used to evaluate the ''crossover modul us'' and ''modulus separation'' theological polydispersity measures an d ii theoretical justification is provided for the modulus separation index. In the past, these empirical methods have been used successfull y to relate molar mass characteristics to theological properties. Resu lts obtained in this study confirm the validity of the modulus separat ion index for linear polymers and suggest that it should be used caref ully in the analysis of data from branched polymers. Linear viscoelast ic data are used to estimate the terminal relaxation time spectra of b oth the linear and branched materials and a new correlation between mo dulus separation and relaxation time polydispersity is given.