Linear rheology of diluted linear, star and model long chain branched polymer melts

We present experiments and theory on the diluted melt dynamics of monodisperse entangled polymers of linear, star and H-shaped architecture. Frequency-dependent rheological data on a series of progressively diluted linear, star and H-polymers are in good agreement with a refined tube-model theory that, for H-polymers, combines star polymer melt behaviour at high frequency, with linear polymer reptation behaviour at low frequencies. Taking into account the effect of dilution via some simple scaling relations, mild polydispersity and by incorporating the high frequency Rouse modes, we are able to model quantitatively the entire frequency range. This work suggests a novel rheological route to analysing long chain branching in polymer melts.