Structural Evolutions of Initially Amorphous Polymers During Near-Tg Stretching: A Minireview of Recent Progresses

Industrial processing of polymeric products often involves stretching from glassy state. Therefore, the understanding of structural evolution of glassy polymers during stretching around glass transition temperatures (T-g) is of fundamental significance to predict suitable processing parameters for industrial purpose. However, former reviews have mostly focused on the structural evolution of polymers being stretched from melt or crystalline state, whereas there still lacks summaries dedicated to stretching studies from the amorphous state. This work summarizes important advances of researches on both non-crystallizable and crystallizable polymers concerning their stretching behavior near T-g. Based on case studies on typical examples of each kind, the review systematically presented the structural changes including chain orientation/relaxation kinetics, dynamic network evolution, and stretch-induced phase transition. A discussion about the influence of these structural evolutions on essential end-use properties of materials is also included, in the hope of providing guidance on future stretching-related studies.