Tensile yield behavior of isotactic polybutene-1

Relative to polyethylene or polypropylene, isotactic polybutene-1 (iPB-1) in form I is of high value for commercial applications due to its excellent mechanical properties; whereas, it tends to exhibit inconspicuous yield behavior closely related to poor energy consumption and thus weak toughness when subjected to uniaxial stretching. Regret, few studies had addressed how to control iPB-1 tensile yield behavior. As the tensile yield behavior of form I iPB-1 depended on the applied annealing temperature Ta and time ta as well as cyclic loading-unloading conditions, iPB-1 three-phase structure evolution was carefully characterized by wide-line solid-state 1H NMR. With Ta or ta increasing, the weakening tensile yield behavior of iPB-1 was accompanied by a decreasing rigid phase content which can be recognized by 1H NMR rather than DSC, revealing that a higher rigid phase content in iPB-1 favors a more significant typical tensile yield behavior. Therefore, the mutual contact possibility, dislocation and slip of iPB-1 rigid phase were proposed to be responsible for the tensile yield behavior. Furthermore, the weakening tensile yield behavior of iPB-1 due to annealing at a higher temperature can slowly recover back while further annealing at a lower temperature, implying the reversibility of destroyed rigid phase. Cyclic loading-unloading under a suitable fixed strain can promote formation of rigid phase in iPB-1, favoring appearance of the typical yield behavior. The results are of significance for understanding the structural origin of tensile yield behavior of iPB-1 and further tuning toughness of iPB-1 for its industrial applications.