Uniaxial Extension of Entangled Polymer Melts close to T$_{\mathrm{g}}$

Transient (nonlinear) responses of entangled polymers to startup deformation indicate a transition from the initial elastic deformation to irreversible deformation (flow) [1-3]. This yielding behavior varies with the applied rate: at a higher rate the entanglement network can be strained to a higher degree before its breakdown. In this work, we subject entangled melts such as polystyrene to startup uniaxial extension to show how yielding takes place as a function of temperature. The objective is to explore whether there would be any mechanical signature of emergence of any secondary structure as the glass transition temperature T$_{\mathrm{g}}$ is approached from above. \\[4pt] [1] S. Q. Wang, S. Ravindranath, Y. Wang and P. Boukany, \textit{J. Chem. Phys}. \textbf{127}, 064903 (2007).\\[0pt] [2] Y. Y. Wang and S. Q. Wang, \textit{J. Rheol}. \textbf{53}, 1389 (2009).\\[0pt] [3] S. Q. Wang, S. Ravindranath and P. E. Boukany, \textit{Macromolecules} \textbf{44}, 183 (2011).