Abstract
Nonlinear shear and uniaxial extensional measurements on a series of graft-polystyrenes with varying average numbers and molar masses of grafted side chains are presented. Step-strain measurements are performed to evaluate the damping functions of the melts in shear. The damping functions show a decreasing dependence on strain with an increase in mass fraction of grafted side chains. Extensional viscosities of the melts of graft-polystyrenes exhibit a growing strain hardening with increasing average number of grafted side chains as long as the side branches have a sufficient molar mass to be entangled. Graft-polystyrenes with side arms below the critical molar mass M c for entanglements of linear polystyrene but above the entanglement molar mass M e of linear polystyrene (M e < M w,br < M c) still show a distinct strain hardening. With decreasing molar mass of the grafted side chains (M w,br < M e) the nonlinear-viscoelastic properties of the graft-polystyrene melts approach the behavior for a linear polystyrene with comparable polydispersity.
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Acknowledgements
Financial support from the German Research Foundation (DFG) (grant numbers Mu 1336/2-1 and Mu 1336/2-3) is gratefully acknowledged. J.H. wants to thank Prof. Dr. M. H. Wagner for the source code of the program for the damping function calculations.
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Hepperle, J., Münstedt, H. Rheological properties of branched polystyrenes: nonlinear shear and extensional behavior. Rheol Acta 45, 717–727 (2006). https://doi.org/10.1007/s00397-005-0031-9
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DOI: https://doi.org/10.1007/s00397-005-0031-9