Interpretation of hysteresis behaviour of PI-PS multigraft copolymers by adapting to the dynamic flocculation model

Hysteresis behaviour of highly elastic multigraft copolymers with a polyisoprene (PI) backbone and branched polystyrene (PS) arms has been interpreted by applying the extended non-affine tube model of filler reinforced rubber elasticity (dynamic flocculation model), which takes into account that conformational fluctuations in bulk networks are strongly suppressed by packing effects. Originally, this model was developed to describe hyperelasticity of unfilled networks, and later, stress softening and hysteresis of filler reinforced elastomer materials like carbon black and silica filled rubbers. The evaluation of stress softening is obtained via pre-strain dependent hydrodynamic amplification of the rubber matrix by a fraction of rigid filler clusters with virgin filler-filler bonds. The filler-induced hysteresis is described by a cyclic breakdown and re-aggregation of the residual fraction of more soft filler clusters with already broken filler-filler bonds. We show, for the first time that the developed concept is in fair agreement with experimental stress-strain data of superelastic PI-PS multigraft copolymers. Depending on the PS-content and their functionality multigraft copolymers form microphase separated structures according to the constituting block copolymer concept, where the PS arms act as multi-domains in a PI matrix. The adaptation of the model is based on the assumption that the PS-domains are acting similar to filler clusters. The obtained microscopic material parameters appear reasonable for the description of the structure and mechanical properties of multigraft copolymers.