Decoding the viscoelastic response of polydisperse star/linear polymer blends

It is well known that polydispersity and branching have important and, at the same time, hardly Predictable effects on the rheological and processing properties of industrial polymers. in the literature, many studies have been undertaken in order to predict the rheology of polydisperse linear polymers and monodisperse, well-defined, branched polymers(1,2). Industrial polymers are usually, simultaneously polydisperse and branched, exhibiting a much more complex viscoelastic behaviour. When polydispersity and branching are both present, many different relaxation processes are indeed active and sometimes coupled. In order to understand the viscoelastic behaviour of such a class of complex materials, we investigated the rheology of several blends of polydisperse linear and stars polymers with the help of a coarse grained - tube model(3,4,5,6). A series of polydisperse star/linear polybutadiene blends characterized by different composition and arm average molecular weight was prepared. Linear "parent" polymers were synthesized via anionic polymerization. A coupling agent was introduced in a second stage in order to obtain the blends. In order to characterize the composition of the blends, light scattering data were performed for determining their molar mass distributions (MMD). Then, using an adequate statistical approach, MMD were divided into different categories of architectures. We obtained a full set of linear and non-linear rheological data. Then, we extended our tube-based model to predict their linear viscoelasticity. This requires several modifications of the initial model in order to deal with a very large number of different particles and star molecules having arms of different lengths. The non-linear rheological response was analyzed with special attention to the time-strain separability at short and long times, whereas the response to uniaxial extension was also investigated.