We investigated the uniaxial deformation behavior of crosslinked low-density polyethylene in partially and substantially molten states using a real-time true stress-strain birefringence system. The stress-bireffingence behavior exhibits a multi-regime behavior during stretching and holding process. The details of this regime behavior are primarily governed by the degree of unmelted crystallinity as it has a dominant role in the long-range structural connectivity. When the long-range physical connectivity is present, a three-regime nonlinear stress-optical behavior was observed. When the long-range connectivity is substantially eliminated at higher temperatures, the regime I behavior disappears. Structural studies including cooling process reveal that the lower the proportion of molten material during stretching, the higher the concentration of fibrillar structure and the shorter are the lengths of the kebabs that exhibit twisted lamellae after solidification. (c) 2005 Wiley Periodicals, Inc.