(180ad) Entangled Polystyrene Melts with Well-Defined Long-Chain Branching in Large Deformation

Most of the past studies have focused on nonlinear responses to large deformation of linear entangled polymers.  Our knowledge is largely insufficient concerning the nonlinear rheological behavior of entangled polymers containing long-chain branching (LCB), apart from the literature work on low-density polyethylene (LDPE).  On the other hand, presence of LCB has been identified as the origin of the so called strain hardening in uniaxial extension of entangled melts.  In this work, we will clarify the origin of strain hardening using several experimental systems including a pair of linear and LCB polyisoprenes and a pair of linear and LCB polystyrenes.  One of the key differences between linear and LCB melts is not that one strain softens and the other hardens, rather, is that linear melts undergo elastic yielding, resulting in specimen breakdown during relaxation from step extension, whereas melts with LCB could resist the structural failure. 

This work, is supported, in part, by a grant from the National Science Foundation (DMR-1105135).